Double-layer preservative film and application thereof in shelf life of sauce-marinated meat products

Abstract

The application provides a double-layer preservative film and application thereof in shelf life of sauce-marinated meat products. The preservative film is double-layered, the outer layer is a hydrophobic layer, and the inner layer is a hydrophilic layer. The hydrophobic layer is obtained by electrospinning of corn alcohol-soluble protein and has a micro-nano structure on the surface. The hydrophilic layer is obtained by casting of citric acid grafted soybean protein isolate, and the film contains liposomes coated with tea seed polyphenols and tea seed polypeptides. The double-layer preservative film can realize directional water expulsion from the outer layer, and water can permeate from the hydrophobic layer to the hydrophilic layer, and vice versa. In the process, the hydrophilic layer remains moist, and the hydrophobic layer remains dry. The liposomes in the hydrophilic layer can release tea seed polypeptides and tea seed polyphenols, achieving the effects of antioxidation, color protection and antibiosis. The hydrophobic layer can slow down the evaporation of water in the sauce-marinated meat, while allowing external water to transport inward, playing a role in maintaining the moisture and tenderness of the sauce-marinated meat. Meanwhile, the dry hydrophobic layer can reduce the growth of bacteria.

Description

Technical Field

[0001] This invention relates to the technical field of food preservation, specifically to a double-layer preservation film and its application in the preservation of braised meat products. Background Technology

[0002] Braised meat products have a history of thousands of years in my country. They are characterized by their convenience, bright color, tender texture, and rich flavor, making them popular among the Chinese people. For a long time, the development of braised meat products in my country was relatively slow. It wasn't until modern times that they moved beyond small family workshops and entered a new stage of industrialized, large-scale production. Currently, the daily consumption of braised meat products in my country reaches approximately 15,000 tons. Small workshops and small-scale production can hardly guarantee product quality and meet consumer demand. Therefore, it is necessary to improve and innovate the traditional processing techniques for braised meat products, making the production process more scientific and the equipment more modern to further improve product quality and meet consumer needs. The preservation and storage of braised meat products is also a major challenge. Some methods directly add preservatives, but with increasing public awareness of food safety, the use of preservatives has been questioned. Low-temperature freezing requires a large amount of energy. Therefore, providing a method that can preserve braised meat products at room temperature while maintaining their quality is an urgent problem to be solved. Summary of the Invention

[0003] Technical Problem to be Solved: To address the aforementioned technical problems, the purpose of this invention is to provide a double-layer preservation film and its application in the preservation of braised meat products. The double-layer film consists of an outer hydrophobic layer and an inner hydrophilic layer, enabling directional water repellency from the outer layer. Water can directionally penetrate from the hydrophobic layer to the hydrophilic layer, but not vice versa. During this process, the hydrophilic layer remains moist, while the hydrophobic layer remains dry. Liposomes within the hydrophilic layer can slowly release tea seed polypeptides and tea seed polyphenols, achieving antioxidant, color-protecting, and antibacterial effects. The hydrophobic layer slows down the evaporation of moisture from the braised meat while allowing external moisture to be transported inward, thus maintaining the moisture and tenderness of the braised meat. Simultaneously, the dry hydrophobic layer reduces bacterial growth.

[0004] Technical solution: A double-layer food preservation film, wherein the food preservation film is double-layered, the outer layer is a hydrophobic layer and the inner layer is a hydrophilic layer; the hydrophobic layer is obtained by electrospinning of zein and has a micro-nano structure on its surface;

[0005] The hydrophilic layer is obtained by casting citric acid-grafted soy protein isolate and contains liposomes encapsulating tea seed polyphenols and tea seed polypeptides.

[0006] Furthermore, the thickness of the hydrophilic layer is 5-8 μm, and the thickness of the hydrophobic layer is 3-5 μm.

[0007] Furthermore, the method for preparing the liposomes coated with tea seed polyphenols and tea seed polypeptides is as follows:

[0008] Step 1: Dissolve 0.5g of gelatin in 50mL of water and heat to obtain a gelatin solution;

[0009] Step 2: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution containing 0.3g of tea seed polyphenols, and evaporate at 40-50℃ to form a film.

[0010] Step 3: Add 200 mL of phosphate buffer solution with pH 6.5-7.4, containing 0.5-0.8 g of tea seed polypeptide and 2 g of polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60 °C to fully hydrate;

[0011] Step 4: Add gelatin solution and ultrasonically stir at 4°C for 1 hour to obtain a suspension;

[0012] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols and tea seed polypeptides.

[0013] The preparation method of the above-mentioned double-layer plastic wrap includes the following steps:

[0014] S1: Take 2 parts of soy protein isolate, add 30 parts of deionized water, adjust the pH to 7-8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0015] S2: Take 8-9 parts of citric acid and add 10-15 parts of deionized water to obtain a citric acid solution;

[0016] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0017] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4-5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0018] S4: Take 10 parts of citric acid-grafted soy protein isolate, 6 parts of glycerol and 0.5-1 parts of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 150-200 parts of deionized water, and stir magnetically for 20 minutes.

[0019] S5: Adjust the pH to 8-9, heat to 70-80℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1MPa for 10 min to obtain the hydrophilic membrane solution;

[0020] S6: Cast the hydrophilic layer membrane solution into a film and dry it at 50°C to obtain the hydrophilic layer;

[0021] S7: Dissolve 0.5 parts of zein in 3-5 parts of 80% acetic acid solution, add nano zinc oxide, and stir evenly to obtain spinning solution;

[0022] S8: An electrospinning device is used for electrospinning. A hydrophilic layer is placed on the receiving plate. After the hydrophobic layer is received, a double-layer plastic wrap is formed.

[0023] Furthermore, in S7, the mass ratio of zein to nano zinc oxide is (2-5):1.

[0024] Furthermore, the electrospinning conditions are as follows: the spinning solution flow rate is 1.5-2.5 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, and the distance between the spinneret and the receiving plate is 15 cm.

[0025] The application method of the above-mentioned double-layer plastic wrap in the preservation of braised meat products is as follows:

[0026] S1: Seal the braised meat products with double-layer plastic wrap;

[0027] S2: Sterilization;

[0028] S3: Further packaging in standard packaging bags for storage.

[0029] Furthermore, the sterilization method employs irradiation sterilization with an irradiation dose of 3-4 kGy.

[0030] Beneficial effects:

[0031] 1. This invention uses a double-layer preservation film. The outer layer is a hydrophobic layer, and the inner layer is a hydrophilic layer, which enables directional water repellency from the outer layer. Water can directionally penetrate from the hydrophobic layer to the hydrophilic layer, but not vice versa. During this process, the hydrophilic layer remains moist, while the hydrophobic layer remains dry. The liposomes in the hydrophilic layer can slowly release tea seed polypeptides and tea seed polyphenols, achieving antioxidant, color-protecting, and antibacterial effects. The hydrophobic layer can slow down the evaporation of moisture in the braised meat, while allowing external moisture to be transported inward, thus maintaining the moisture and tenderness of the braised meat. At the same time, the dry hydrophobic layer can reduce bacterial growth.

[0032] 2. The hydrophobic layer surface of the present invention has a micro-nano structure, which is composed of micron-sized pores and nano-zinc oxide. Zein itself has a certain degree of hydrophobicity. After adding the micro-nano structure, the hydrophobicity is further improved, and the contact angle can reach 151.0°. At the same time, the nano-zinc oxide in the micro-nano structure has good antibacterial properties and can improve the mechanical properties of the hydrophobic layer.

[0033] 3. In this invention, the hydrophilic layer is obtained by grafting citric acid onto soy protein isolate through casting. The carboxyl groups of citric acid react with the amino groups in soy protein isolate to form amide bonds or other types of chemical bonds, which are grafted onto soy protein isolate, increasing the number of carboxyl groups on the protein molecules, thereby improving the hydrophilicity of the soy protein isolate membrane and forming a good water retention effect for braised meat.

[0034] 4. In this invention, the soy protein isolate membrane contains liposomes that encapsulate tea seed polyphenols and tea seed polypeptides. The addition of gelatin can improve the stability of the liposomes and increase the encapsulation rate of tea seed polyphenols and tea seed polypeptides. On the other hand, it can create a temperature response. During the preservation of braised meat, if the temperature rises, the release of tea seed polyphenols and tea seed polypeptides in the liposomes will be accelerated, thus regulating the preservation process.

[0035] 5. In this invention, the nano zinc oxide exists in the outer hydrophobic layer and does not come into direct contact with the braised meat, nor does it migrate, making it safer to use and more likely to be favored by consumers. Detailed Implementation

[0036] This invention proposes a double-layer preservation film and its application in the preservation of braised meat products. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following will provide a more detailed description of the invention with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0037] Example 1

[0038] The method for preparing liposomes coated with tea seed polyphenols and tea seed polypeptides is as follows:

[0039] Step 1: Dissolve 0.5g of gelatin in 50mL of water and heat to obtain a gelatin solution;

[0040] Step 2: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution containing 0.3g of tea seed polyphenols, and evaporate at 40℃ to form a film.

[0041] Step 3: Add 200 mL of phosphate buffer solution with pH 7.2 containing 0.5 g tea seed polypeptide and 2 g polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60 °C to fully hydrate;

[0042] Step 4: Add gelatin solution and ultrasonically stir at 4°C for 1 hour to obtain a suspension;

[0043] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols and tea seed polypeptides.

[0044] Example 2

[0045] The method for preparing liposomes coated with tea seed polyphenols and tea seed polypeptides is as follows:

[0046] Step 1: Dissolve 0.5g of gelatin in 50mL of water and heat to obtain a gelatin solution;

[0047] Step 2: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution containing 0.3g of tea seed polyphenols, and evaporate at 40℃ to form a film.

[0048] Step 3: Add 200 mL of phosphate buffer solution with pH 7.2, containing 0.8 g of tea seed peptide and 2 g of polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60 °C to fully hydrate;

[0049] Step 4: Add gelatin solution and ultrasonically stir at 4°C for 1 hour to obtain a suspension;

[0050] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols and tea seed polypeptides.

[0051] Comparative Example 1

[0052] The difference between this invention and Example 2 is that gelatin is not added, as detailed below:

[0053] The method for preparing liposomes coated with tea seed polyphenols and tea seed polypeptides is as follows:

[0054] Step 1: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution containing 0.3g of tea seed polyphenols, and evaporate at 40℃ to form a film.

[0055] Step 3: Add 200 mL of phosphate buffer solution with pH 7.2, containing 0.8 g of tea seed peptide and 2 g of polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60 °C to fully hydrate;

[0056] Step 4: Ultrasonic stirring at 4℃ for 1 hour to obtain a suspension;

[0057] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols and tea seed polypeptides.

[0058] Comparative Example 2

[0059] The difference between this invention and Example 2 is that tea seed polypeptides are not added; instead, tea seed polyphenols are used, as detailed below:

[0060] The preparation method of tea seed polyphenol liposomes is as follows:

[0061] Step 1: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution containing 1.1g of tea seed polyphenols, and evaporate at 40℃ to form a film.

[0062] Step 3: Add 200 mL of phosphate buffer solution with pH 7.2 and a concentration of 0.01 mol / L containing 2 g of polysorbate-80, shake and mix at 60 °C to fully hydrate;

[0063] Step 4: Ultrasonic stirring at 4℃ for 1 hour to obtain a suspension;

[0064] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols.

[0065] Comparative Example 3

[0066] The difference between this invention and Example 2 is that tea seed polyphenols are not added; instead, tea seed polypeptides are used, as detailed below:

[0067] The preparation method of tea seed polypeptide liposomes is as follows:

[0068] Step 1: Dissolve 3g of lecithin and 1g of cholesterol in 100mL of chloroform, add 50mL of anhydrous ethanol solution, and rotary evaporate at 40℃ to form a film;

[0069] Step 3: Add 200 mL of phosphate buffer solution with pH 7.2 containing 1.1 g of tea seed polypeptide and 2 g of polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60 °C to fully hydrate;

[0070] Step 4: Ultrasonic stirring at 4℃ for 1 hour to obtain a suspension;

[0071] Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polypeptides.

[0072] The encapsulation efficiency and average particle size of tea seed polyphenols and tea seed polypeptides in the liposomes of the above examples and comparative examples were determined respectively, and the results are shown in the table below:

[0073] Table 1

[0074] Encapsulation rate of tea seed polyphenols (%) Tea seed polypeptide encapsulation rate (%) Average particle size (nm) Example 1 77.6 74.5 82.8 Example 2 78.1 74.7 82.9 Comparative Example 1 74.5 71.2 71.4 Comparative Example 2 70.6 - 82.0 Comparative Example 3 - 69.3 80.2

[0075] The following examples all use the liposomes coated with tea seed polyphenols and tea seed polypeptides prepared in Example 2.

[0076] Example 3

[0077] A method for preparing a double-layer food preservation film includes the following steps:

[0078] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0079] S2: Take 80g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0080] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0081] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0082] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0083] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0084] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0085] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0086] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0087] Example 4

[0088] A method for preparing a double-layer food preservation film includes the following steps:

[0089] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0090] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0091] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0092] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0093] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0094] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0095] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0096] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0097] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0098] Example 5

[0099] A method for preparing a double-layer food preservation film includes the following steps:

[0100] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0101] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0102] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0103] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0104] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.5g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0105] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0106] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0107] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0108] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0109] Example 6

[0110] A method for preparing a double-layer food preservation film includes the following steps:

[0111] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0112] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0113] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0114] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0115] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 1.0g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0116] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0117] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0118] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0119] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0120] Example 7

[0121] A method for preparing a double-layer food preservation film includes the following steps:

[0122] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0123] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0124] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0125] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0126] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0127] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0128] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 5μm;

[0129] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0130] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0131] Example 8

[0132] A method for preparing a double-layer food preservation film includes the following steps:

[0133] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0134] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0135] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0136] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0137] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0138] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0139] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 8μm;

[0140] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0141] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0142] Example 9

[0143] A method for preparing a double-layer food preservation film includes the following steps:

[0144] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0145] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0146] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0147] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0148] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0149] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0150] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0151] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.1g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0152] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0153] Example 10

[0154] A method for preparing a double-layer food preservation film includes the following steps:

[0155] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0156] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0157] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0158] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0159] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0160] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0161] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0162] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.25g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0163] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0164] Example 11

[0165] A method for preparing a double-layer food preservation film includes the following steps:

[0166] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0167] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0168] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0169] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0170] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0171] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0172] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0173] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0174] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 1.5 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0175] Example 12

[0176] A method for preparing a double-layer food preservation film includes the following steps:

[0177] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0178] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0179] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0180] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0181] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0182] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0183] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0184] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0185] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.5 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0186] Example 13

[0187] A method for preparing a double-layer food preservation film includes the following steps:

[0188] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0189] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0190] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0191] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0192] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0193] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0194] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0195] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0196] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: spinning solution flow rate is 2.0 mL / h, spinning temperature is 25℃, spinning voltage is 18 kV, air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 3 μm.

[0197] Example 14

[0198] A method for preparing a double-layer food preservation film includes the following steps:

[0199] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0200] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0201] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0202] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0203] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0204] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0205] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0206] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0207] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 5 μm.

[0208] Comparative Example 4

[0209] The difference between this comparative example and Example 4 is that citric acid is not used to graft soy protein isolate, as detailed below:

[0210] A method for preparing a double-layer food preservation film includes the following steps:

[0211] S1: Take 10g of soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0212] S2: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0213] S3: The hydrophilic layer film solution is cast into a film and dried at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0214] S4: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0215] S5: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0216] Comparative Example 5

[0217] The difference between this comparative example and Example 4 is that the liposomes prepared in Comparative Example 1 are used, as detailed below:

[0218] A method for preparing a double-layer food preservation film includes the following steps:

[0219] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0220] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0221] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0222] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0223] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes prepared in Comparative Example 1, add 180g of deionized water and stir magnetically for 20min.

[0224] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0225] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0226] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0227] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0228] Comparative Example 6

[0229] The difference between this comparative example and Example 4 is that the liposomes prepared in Comparative Example 2 are used, as detailed below:

[0230] A method for preparing a double-layer food preservation film includes the following steps:

[0231] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0232] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0233] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0234] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0235] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes prepared in Comparative Example 2, add 180g of deionized water and stir magnetically for 20min.

[0236] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0237] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0238] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0239] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0240] Comparative Example 7

[0241] The difference between this comparative example and Example 4 is that the liposomes prepared in Comparative Example 3 are used, as detailed below:

[0242] A method for preparing a double-layer food preservation film includes the following steps:

[0243] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0244] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0245] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0246] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0247] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes prepared in Comparative Example 3, add 180g of deionized water and stir magnetically for 20min.

[0248] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0249] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0250] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0251] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0252] Comparative Example 8

[0253] The difference between this comparative example and Example 4 is that nano-zinc oxide is not used, as detailed below:

[0254] A method for preparing a double-layer food preservation film includes the following steps:

[0255] S1: Take 20g of soy protein isolate, add 300g of deionized water, adjust the pH to 8, heat to 90℃ and stir to obtain soy protein isolate solution;

[0256] S2: Take 90g of citric acid and add 130g of deionized water to obtain a citric acid solution;

[0257] S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete.

[0258] S3: Cool to room temperature, add food-grade hydrochloric acid, adjust pH to 4.5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate;

[0259] S4: Take 10g of citric acid-grafted soy protein isolate, 6g of glycerol and 0.8g of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 180g of deionized water and stir magnetically for 20min.

[0260] S5: Adjust the pH to 8.5, heat to 70℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution;

[0261] S6: Cast the hydrophilic layer solution into a film and dry it at 50°C to obtain a hydrophilic layer with a thickness of 7μm;

[0262] S7: Dissolve 0.5g of zein in 5g of 80% acetic acid solution, add 0.2g of nano zinc oxide, and stir evenly to obtain spinning solution;

[0263] S8: Electrospinning is performed using an electrospinning device. The electrospinning conditions are as follows: the spinning solution flow rate is 2.0 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, the distance between the spinneret and the receiving plate is 15 cm, a hydrophilic layer is placed on the receiving plate, and after the hydrophobic layer is received, a double-layer preservation film is formed with a hydrophobic layer thickness of 4 μm.

[0264] Determine the static contact angle and roll-off angle of the hydrophobic layer;

[0265] The mechanical properties of the double-layer plastic wrap were determined, including tensile strength and elongation at break. A texture analyzer was used to measure the tensile strength and elongation at break of the double-layer plastic wrap samples. The tensile rate was 15 mm / min, and each sample was tested in triplicate. The results are shown in Table 2.

[0266] Table 2

[0267]

[0268]

[0269] Note: "-" indicates not measured.

[0270] The antibacterial properties of the double-layer plastic wrap prepared in Example 4 and the comparative example were determined. Referring to QB / T 2591-2003 "Test Methods and Antibacterial Effects of Antibacterial Plastics" and "Disinfection Technical Specifications," the prepared double-layer plastic wrap was incubated with a certain amount of bacterial suspension for a period of time. Colony counts were performed according to GB 4789.2-2022 "Food Hygiene Microbiological Examination: Determination of Total Colony Count" to determine the antibacterial properties of the double-layer plastic wrap. The results are shown in Table 3.

[0271] Table 3

[0272]

[0273]

[0274] Example 15

[0275] The application of double-layer plastic wrap in the preservation of braised meat products is as follows:

[0276] S1: The braised meat products are sealed and packaged using the double-layer plastic wrap prepared in Example 4;

[0277] S2: Irradiation sterilization, irradiation dose is 3.5 kGy;

[0278] S3: Further packaging in standard packaging bags for storage.

[0279] Comparative Example 9

[0280] The difference between this comparative example and Example 15 is that the double-layer plastic wrap prepared in Comparative Example 4 is used.

[0281] Comparative Example 10

[0282] The difference between this comparative example and Example 15 is that the double-layer plastic wrap prepared in Comparative Example 5 is used.

[0283] Comparative Example 11

[0284] The difference between this comparative example and Example 15 is that the double-layer plastic wrap prepared in Comparative Example 6 is used.

[0285] Comparative Example 12

[0286] The difference between this comparative example and Example 15 is that the double-layer plastic wrap prepared in Comparative Example 7 is used.

[0287] Comparative Example 13

[0288] The difference between this comparative example and Example 15 is that the double-layer plastic wrap prepared in Comparative Example 8 is used.

[0289] Total bacterial count: determined according to the plate count method in national standard GB / T4789.2-2022, with 3 plates for each dilution gradient.

[0290] Volatile basic nitrogen: The volatile basic nitrogen of braised meat products was determined using a fully automated Kjeldahl nitrogen analyzer based on the principle of semi-micro nitrogen determination.

[0291] Sensory evaluation: A scoring group of 10 teachers and students from this college will conduct sensory evaluation, and the evaluation criteria are shown in Table 4 below.

[0292] Table 4 Sensory Evaluation Criteria for Braised Meat Products

[0293]

[0294]

[0295] After being stored at room temperature (24-26℃) for 20 days, the total bacterial count, volatile basic nitrogen, and sensory evaluation of the braised meat products were performed. The results are shown in Table 5 below:

[0296] Table 5

[0297]

[0298] As can be seen from Table 5, the total bacterial counts of Examples 13-15 were all low, fully complying with the requirements of the Hygienic Standard for Cooked Meat Products (GB2726-2016), which stipulates that the total bacterial count of braised meat is ≤4.91g (CFU / g).

[0299] Simultaneously, after storing Examples 15 and 10 at high temperature (37-38℃) for 20 days, their total bacterial count, volatile basic nitrogen, and sensory evaluation were determined. The results are shown in Table 6.

[0300] Table 6

[0301]

Claims

1. A double-layer food preservation film, characterized in that, The plastic wrap is double-layered, with an outer hydrophobic layer and an inner hydrophilic layer. The hydrophobic layer is obtained by electrospinning of zein and has a micro-nano structure on its surface. The hydrophilic layer is obtained by casting citric acid-grafted soy protein isolate and contains liposomes encapsulating tea seed polyphenols and tea seed polypeptides. The method for preparing the liposomes coated with tea seed polyphenols and tea seed polypeptides is as follows: Step 1: Dissolve 0.5g of gelatin in 50mL of water and heat to obtain a gelatin solution; Step 2: Dissolve 3g of lecithin and 1g of cholesterol in 100 mL of chloroform, add 50 mL of anhydrous ethanol solution containing 0.3g of tea seed polyphenols, and evaporate at 40-50℃ to form a film. Step 3: Add 200 mL of phosphate buffer solution with a pH of 6.5-7.4, containing 0.5-0.8 g of tea seed polypeptide and 2 g of polysorbate-80 at a concentration of 0.01 mol / L, shake and mix at 60°C to fully hydrate; Step 4: Add gelatin solution and ultrasonically stir at 4°C for 1 hour to obtain a suspension; Step 5: Centrifuge and dry to obtain liposomes coated with tea seed polyphenols and tea seed polypeptides; The preparation method is as follows: S1: Take 2 parts of soy protein isolate, add 30 parts of deionized water, adjust the pH to 7-8, heat to 90℃ and stir to obtain soy protein isolate solution; S2: Take 8-9 parts of citric acid and add 10-15 parts of deionized water to obtain a citric acid solution; S3: Cool the soy protein isolate solution to 60°C, add citric acid solution dropwise at a rate of 1 drop / s, and stir the reaction for 1-2 hours after the addition is complete; cool to room temperature, add food-grade hydrochloric acid, adjust the pH to 4-5, centrifuge, and dry to obtain citric acid-grafted soy protein isolate. S4: Take 10 parts of citric acid-grafted soy protein isolate, 6 parts of glycerol and 0.5-1 parts of liposomes coated with tea seed polyphenols and tea seed polypeptides, add 150-200 parts of deionized water, and stir magnetically for 20 min. S5: Adjust the pH to 8-9, heat to 70-80℃, keep warm for 30 min, cool to room temperature, degas under a vacuum of 0.1 MPa for 10 min to obtain the hydrophilic membrane solution; S6: Cast the hydrophilic layer membrane solution into a film and dry it at 50°C to obtain the hydrophilic layer; S7: Dissolve 0.5 parts of zein in 3-5 parts of 80% acetic acid solution, add nano zinc oxide, and stir evenly to obtain spinning solution; S8: An electrospinning device is used for electrospinning. A hydrophilic layer is placed on the receiving plate. After the hydrophobic layer is received, a double-layer plastic wrap is formed.

2. The double-layer food preservation film according to claim 1, characterized in that, The thickness of the hydrophilic layer is 5-8 μm, and the thickness of the hydrophobic layer is 3-5 μm.

3. The double-layer food preservation film according to claim 1, characterized in that, The hydrophobic layer has micron-sized pores with a diameter of 0.1-0.8 μm.

4. The double-layer food preservation film according to claim 1, characterized in that, The mass ratio of zein to nano zinc oxide in S7 is (2-5):

1.

5. A double-layer food preservation film according to claim 1, characterized in that, The nano-zinc oxide in S7 has a particle size of 15-35 nm.

6. The double-layer food preservation film according to claim 1, characterized in that, The electrospinning conditions are as follows: the spinning solution flow rate is 1.5-2.5 mL / h, the spinning temperature is 25℃, the spinning voltage is 18 kV, the air humidity is 50%, and the distance between the spinneret and the receiving plate is 15 cm.

7. The application of a double-layer preservation film according to any one of claims 1-6 in the preservation of braised meat products, characterized in that: The application method is as follows: S1: Seal the braised meat products with double-layer plastic wrap; S2: Sterilization; S3: Further packaging in standard packaging bags for storage.

8. The application of a double-layer preservation film according to claim 7 in the preservation of braised meat products, characterized in that, The sterilization method employs irradiation sterilization, with an irradiation dose of 3-4 kGy.

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