A nano intelligent indicating film with dual effects of meat preservation and freshness visualization and a preparation method thereof

Abstract

The application discloses a kind of meat preservation and freshness visual double-effect nano intelligent indicating film and preparation method thereof, belong to food packaging storage and detection technical field.The preparation method of the intelligent indicating film includes the following steps: (1) poly-3-hydroxybutyric acid-co-oxyvalerate (PHBV) and ferulic acid are dissolved in chloroform solution;(2) polyvinyl alcohol (PVA), konjac glucomannan (KGM), alizarin (AL) are mixed, and polyvinyl alcohol-konjac glucomannan-alizarin mixed solution is obtained by removing bubble;(3) PH-F solution is dried by electrospinning technology, and PVA-KGM-AL@PH-F double-layer indicating film is obtained.The application prepares meat freshness indicating film with efficient antibacterial performance and high sensitivity color response performance by regulating the pH of film-forming solution.In the intelligent indicating film, alizarin responds to meat spoilage biogenic amine, and the color of indicating film gradually changes from cream (slightly yellow) to light pink or even deep purple;By comparing the intelligent indicating film after reflection with colorimetric card, the freshness of meat can be judged.

Description

Technical Field

[0001] This invention relates to a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization, and its preparation method, belonging to the field of food packaging, storage and detection technology. Background Technology

[0002] Meat has always been a core source of nutrition for the human body, providing protein, minerals, and vitamins. However, the quality and safety of meat are highly dependent on the hygiene and temperature control of the cold chain process, including production, storage, distribution, and transportation. With rising living standards, people have increasingly higher demands for the quality of fresh meat, and many consumers suspect that meat products transported via the cold chain may not meet freshness and quality standards. Traditional methods for testing meat freshness have drawbacks such as complex testing processes, compromise on food integrity, long processing times, and high costs. Fat oxidation and microbial contamination are two major factors leading to food spoilage. These changes are often accompanied by the production of specific alkaline or acidic chemicals. The increase in total volatile basic nitrogen (TVB-N) during meat storage gradually alters the environment inside the packaging, making it more alkaline, which can be detected by smart films.

[0003] In recent years, smart films based on chemical dyes have been used to indicate the freshness of meat and meat products. These novel smart films offer advantages such as low cost, real-time detection, biodegradability, and ease of use. However, these chemical dyes are highly toxic, posing adverse effects on human health and the environment. Therefore, safe, non-toxic, and biodegradable natural pigments are highly favored by researchers. Alizarin (1,2-dihydroxyanthraquinone), also known as Turkish Red, is an alcohol-soluble natural food coloring extracted from the roots of the madder plant. The molecular structure of alizarin changes with pH by linking a hydroxyl group to a carbonyl oxygen atom, allowing proton transfer via intramolecular hydrogen bonds. The color varies depending on acidity or alkalinity, ranging from yellow at low pH to purple at high pH. Alizarin has excellent potential for detecting pH changes and is a natural and safe freshness indicator. Phenolic acids are secondary metabolites found in plants, including fruits, vegetables, and grains. Numerous in vitro and in vivo studies have demonstrated that phenolic acids possess antioxidant and antibacterial properties. Adding phenolic acids to films as antibacterial agents imparts a preservative effect, extending the shelf life of food.

[0004] Fresh meat loses juices during storage, which can burden the film with moisture. Therefore, highly permeable films are unsuitable for packaging fresh meat. In high-humidity environments, packaging films need strong moisture-proof properties to ensure that the meat juices do not soak into the film, maintaining the integrity of the packaging. The color change of the indicator film is mainly controlled by volatile biogenic amines or sulfides produced during meat storage. If the indicator film is soaked with juices, the indicator is easily affected and will not display a color consistent with freshness. Smart indicator films require toughness, wear resistance, and high stability, which necessitates excellent mechanical strength. Therefore, polymer materials with good mechanical properties and moisture barrier properties must be selected for the preparation of smart indicator films. To avoid adverse environmental impacts, the film-forming substrate of smart indicator films is often made of safe, non-toxic, sustainable, green, and biodegradable materials, such as polysaccharides, proteins, and some synthetic polymers. This invention selects polyvinyl alcohol (PVA) and konjac glucomannan (KGM) as film-forming substrates, embeds alizarin, and uses electrospinning technology to form a film-forming process to prepare a visual sensing layer for meat freshness. Simultaneously, this invention uses poly-3-hydroxybutyrate-co-vitamin O (PHBV) and ferulic acid to prepare an antibacterial layer, which, combined with the sensing layer, gives the film a dual function of freshness indication.

[0005] In practical applications, indicator films can be severely affected by high humidity environments due to the hydrophilicity of natural pH-sensitive dyes and polymer substrates, especially in fresh meat packaging. Over time, the pH-sensitive dyes in the film may leach out, and the polymer matrix may be damaged by water vapor, affecting the color stability of the indicator. This invention utilizes PHBV material to create an inner waterproof membrane, which reduces the impact of water vapor in the packaging on the polymer matrix carrying the indicator, without affecting its color response to meat freshness, while also providing antibacterial and preservation effects. Summary of the Invention

[0006] The purpose of this invention is to provide a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization, and its preparation method. This intelligent indicator film consists of a sensing layer and a preservation layer. In the sensing layer, alizarin responds to meat spoilage by producing biogenic amines, making the environment inside the packaging alkaline, and the color of the intelligent indicator film changes from milky white / pale yellow to light pink / purple. The preservation layer is a high-porosity nanofiber layer prepared by electrospinning using poly-3-hydroxybutyrate-co-oxyvitamin (PHBV) and ferulic acid as raw materials, extending the shelf life of food while reducing the influence of water vapor on the sensing layer.

[0007] The technical solution of the present invention will be described in detail below:

[0008] First, the present invention provides a method for preparing a freshness indicator film, comprising:

[0009] (1) Dissolve poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid to obtain a pH-F solution;

[0010] (2) The PH-F solution was dried by electrospinning and the fibers were collected on aluminum foil to obtain a PH-F membrane as an antibacterial layer;

[0011] (3) Mix polyvinyl alcohol (PVA) and konjac glucomannan (KGM) to obtain a PVA / KGM mixed solution; add alizarin (AL) to the mixed solution, adjust the pH, stir continuously and homogenize, and then remove bubbles to obtain a PVA-KGM-AL mixed solution.

[0012] (4) The AL-PVA / KGM mixed solution is coated onto the PH-F membrane again by electrospinning technology as a color development layer. The base film is removed to obtain the PVA-KGM-AL@PH-F double-layer preservation indicator film.

[0013] Further, in step (1), the PH-F solution is obtained by dissolving poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid in chloroform and stirring at a temperature of 55°C until completely dissolved;

[0014] Furthermore, in step (3), the PVA-KGM mixed solution is obtained by fully hydrating polyvinyl alcohol and konjac glucomannan powder in ultrapure water and stirring at a temperature of 90°C for about 2 hours until completely dissolved;

[0015] Furthermore, in step (3), the PVA-KGM-AL mixed solution is obtained by adjusting the pH to 4.0~5.0, then stirring, homogenizing, and sonicating.

[0016] Preferably, in step (1), poly-3-hydroxybutyrate-co-oxyvitamin (PHBV) is mixed with chloroform, and the concentration of PHBV is 5 to 7 wt%, more preferably 7 wt%.

[0017] Preferably, in step (3), polyvinyl alcohol (PVA) and konjac glucomannan (KGM) are mixed and stirred, and the concentration of polyvinyl alcohol is 6~8wt%, more preferably 8wt%.

[0018] Preferably, in step (3), the concentration of alizarin is 1~2 mg / ml, more preferably 1 mg / ml.

[0019] Advantages and beneficial effects of the present invention:

[0020] 1. This invention uses polyvinyl alcohol, konjac glucomannan, natural alizarin, ferulic acid, and poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) to prepare a nano-preservation smart indicator film. Therefore, the preservation indicator film is non-toxic, low in cost, and has good biodegradability, which is in line with the trend of green packaging and sustainable development.

[0021] 2. Poly(3-hydroxybutyrate-co-oxyvitamin) (PHBV) is a biomaterial produced from starch using fermentation engineering technology. It exhibits excellent stability, water resistance, and biodegradability, and does not pollute the environment. This invention selects PHBV as the antibacterial layer matrix, which can both combine with ferulic acid for its preservative effect and separate the sensing layer from water molecules on the meat surface, effectively reducing the impact of water vapor in the packaging on the polymer matrix carrying the indicator.

[0022] 3. The electrospinning technology utilizes simple and easy-to-operate equipment, producing nanofibers with advantages such as large specific surface area and porosity. Furthermore, research has found that nanofibers with relatively higher porosity and larger specific surface area are more sensitive to changes in the surrounding pH and can also regulate the release of functional substances. This invention uses electrospinning technology to prepare a nanobilayer indicator membrane, which is beneficial for increasing the membrane's sensitivity to changes in the surrounding pH and can also regulate the release of alizarin, improving alizarin's sensitivity and color response.

[0023] 4. This invention uses electrospinning technology to prepare a nano-bilayer indicator membrane. The prepared nanofiber membrane is white or light yellow, which contrasts sharply with the color of the meat itself (bright red). After the alizarin in the sensing layer responds to the color, the color change can be easily observed, reducing the difficulty of monitoring and identifying the freshness of meat. Attached Figure Description

[0024] 1. Figure 1 This is a color change diagram of alizarin used in this invention under pH conditions of 3-12. At pH 3-4, the solution is pale yellowish-brown. As the pH value increases to 5-7, the solution color gradually changes to pale pink and the color intensity increases. At pH 8, the solution is crimson; at pH 9, the solution is purplish-red; at pH 10, the solution is purple; and at pH 12, the solution is bluish-purple.

[0025] 2. Figure 2 This is the UV-Vis absorption spectrum of alizarin solution under pH conditions ranging from 3 to 13. At pH 13, the absorption peaks of alizarin solution are near wavelengths of 575 nm and 610 nm. As the pH decreases, the absorption peak wavelength of alizarin gradually shifts towards 520 nm.

[0026] 3. Figure 3These are Fourier transform infrared (FTIR) spectra of the PVA-KGM-AL@PH-F bilayer indicator film, the PVA-KGM-AL indicator film, and the PH-F antibacterial film. The spectrum of the PVA-KGM-AL@PH-F bilayer indicator film is a combination of the spectra of the PVA-KGM-AL indicator film and the PH-F film, indicating that the bilayer structure is not a simple overlap, but rather bonded together by electrostatic interactions.

[0027] 4. Figure 4 This is a flowchart illustrating the preparation process and a simple application of the present invention.

[0028] 5. Figure 5 The results of water vapor permeability measurement of the double-layer indicator film prepared in Example 1 of this invention are shown. The water vapor permeability of the PVA-KGM-AL@PH-F double-layer indicator film, PVA-KGM-AL indicator film, PH-F antibacterial film, P / P double-layer film, and Gel-K antibacterial film were measured using the permeation cup method. Different lowercase letters represent significant differences (p < 0.05). PHBV is a non-water-soluble material. Films with PHBV as the base film have low water vapor permeability and good moisture-proof performance. When a double-layer structure is formed, the PVA-KGM-AL@PH-F double-layer indicator film has even lower water vapor permeability and the best water vapor barrier properties. The overlapping double-layer film PK / P has a reduced water vapor permeability compared to a single-layer film, but it is still lower than that of the PVA-KGM-AL@PH-F double-layer indicator film.

[0029] 6. Figure 6 The mechanical properties of the double-layer indicator film prepared in Example 1 of this invention were measured. The tensile strength (TS) and elongation at break (EAB%) of the PVA-KGM-AL@PH-F double-layer indicator film, PVA-KGM-AL indicator film, PH-F antibacterial film, P / P double-layer film, and Gel-K antibacterial film were measured using the ASTM D882-88 standard method. Different lowercase letters represent significant differences (p < 0.05). The PH-F antibacterial film showed poor strength and toughness. After forming a double-layer film with the PVA-KGM-AL indicator film, the double-layer film exhibited good strength and toughness. During the test, the P / P film showed a pattern where one layer broke first, followed by the other. Although its tensile strength and elongation at break were similar to those of the PVA-KGM-AL@PH-F double-layer indicator film, the dual-function of the film was compromised, making it difficult to achieve the expected results.

[0030] 7. Figure 7 The antibacterial effect of the double-layer preservation indicator film prepared in Example 1 of this invention is shown. Under the same culture conditions, the number of colonies in Figure (b) is significantly less than that in Figure (a), indicating that the PVA-KGM-AL@PH-F double-layer indicator film prepared in this invention has a better antibacterial effect. Detailed Implementation

[0031] The technical solution of the present invention will be described in further detail below, but the scope of protection of the present invention is not limited to the following description.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0033] Example 1

[0034] (1) Dissolve 7 wt% poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid in chloroform and stir at 55°C for 2 h to obtain PH-F solution;

[0035] (2) The PH-F solution described in (1) is electrospun and dried. The electrospinning conditions are: No. 22 needle, flow rate of 0.2 mL / min, and aluminum foil is used as the spindle fiber receiving layer. Finally, the base film is removed to obtain the PH-F film as the antibacterial layer.

[0036] (3) Mix 8 wt% polyvinyl alcohol (PVA) and 2 wt% konjac glucomannan (KGM) and dissolve at 90°C for 2-3 hours. After cooling, a PVA / KGM mixed solution is obtained. Add 1 mg / mL alizarin (AL) to the above PVA / KGM mixed solution, adjust the pH to 4.0, stir continuously and homogenize, and then remove bubbles to obtain an AL-PVA / KGM mixed solution.

[0037] (4) The AL-PVA / KGM mixed solution described in (3) is coated onto a PH-F membrane using electrospinning technology as a color development layer, thus obtaining a PVA-KGM-AL@PH-F double-layer preservation indicator film. The electrospinning conditions are: No. 21 needle, flow rate of 0.2 mL / min, and PH-F membrane as the spindle fiber receiving layer.

[0038] This embodiment presents a dual-layer nano-indicator film for meat preservation and freshness visualization, employing an optimal ratio of various film-forming substrates. The resulting dual-layer nano-indicator film is light milky white in color, exhibits good moisture-proof properties, and demonstrates more sensitive and obvious color changes in meat freshness monitoring. When this intelligent indicator film is used to determine the freshness of fresh beef: the intelligent patch is applied to the surface of fresh meat and sealed for 20-30 minutes. If the indicator film changes color from white to pink or purple, it indicates that the beef is no longer fresh or is even in a state of spoilage and is no longer suitable for consumption.

[0039] Example 2

[0040] (1) Dissolve 7 wt% poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid in chloroform and stir at 55°C for 2 h to obtain PH-F solution;

[0041] (2) The PH-F solution described in (1) is subjected to electrospinning and drying. The electrospinning conditions are: No. 22 needle, flow rate of 0.2 mL / min, and aluminum foil is used as the spindle fiber receiving layer. Finally, the base film is removed to obtain the PH-F film.

[0042] (3) Mix 6 wt% polyvinyl alcohol (PVA) and 2 wt% konjac glucomannan (KGM) and dissolve at 90°C for 2-3 hours. After cooling, a PVA / KGM mixed solution is obtained. Add 0.5 mg / mL alizarin (AL) to the above PVA / KGM mixed solution, adjust the pH to 4.0, stir continuously and homogenize, and then remove bubbles to obtain an AL-PVA / KGM mixed solution.

[0043] (4) The PVA-KGM-AL mixed solution described in (3) is coated onto a PH-F membrane using electrospinning technology to form a color development layer, thus obtaining a PVA-KGM-AL@PH-F double-layer indicator membrane. The electrospinning conditions are: No. 21 needle, flow rate of 0.2 mL / min, and the PH-F membrane is used as the spindle fiber receiving layer.

[0044] This embodiment presents a double-layer nano-indicator film for meat preservation and freshness visualization, along with its preparation method. Adding a low concentration of indicator results in a white double-layer nano-indicator film with good moisture-proof properties. However, when the indicator concentration is too low, the color change is faint and difficult to observe with the naked eye. The freshness indicator color of this film ranges from white to light pink, with subtle color changes, making it unsuitable for monitoring beef freshness.

[0045] Example 3

[0046] (1) Dissolve 7wt% poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid in chloroform and stir at 55°C for 2 hours to obtain PH-F solution;

[0047] (2) The PH-F solution described in (1) is subjected to electrospinning and drying. The electrospinning conditions are: No. 22 needle, flow rate of 0.2 mL / min, and aluminum foil is used as the spindle fiber receiving layer. Finally, the base film is removed to obtain the PH-F film.

[0048] (3) Mix 8 wt% polyvinyl alcohol (PVA) and 2 wt% konjac glucomannan (KGM) and dissolve at 90°C for 2-3 hours. After cooling, a PVA / KGM mixed solution is obtained. Add 2 mg / mL alizarin (AL) to the above PVA / KGM mixed solution, adjust the pH to 4.0, stir continuously and homogenize, and then remove bubbles to obtain an AL-PVA / KGM mixed solution.

[0049] (4) The AL-PVA / KGM mixed solution described in (3) is coated onto a PH-F membrane using electrospinning technology to form a color development layer, thus obtaining an AL-PVA-KGM@PH-F bilayer indicator membrane. The electrospinning conditions are: a No. 21 needle, a flow rate of 0.2 mL / min, and the PH-F membrane as the spindle fiber receiving layer.

[0050] This embodiment presents a bilayer nano-indicator film for meat preservation and freshness visualization, along with its preparation method. Adding a high concentration of indicator results in a yellow bilayer nano-indicator film with good moisture-proof properties. However, excessively high indicator concentrations can cause discontinuous spinning and reduce the tensile strength of the color-developing layer film. The freshness indicator film displays colors ranging from yellow to deep purplish-red or even deep purple, with very pronounced color changes. However, due to its high color saturation, it is not suitable for distinguishing the degree of spoilage.

[0051] Example 4

[0052] (1) Mix 7 wt% polyvinyl alcohol (PVA) and 2 wt% konjac glucomannan (KGM) and dissolve at 90°C for 2-3 hours. After cooling, a PVA / KGM mixed solution is obtained. Add 1.5 mg / mL alizarin (AL) to the above PVA / KGM mixed solution, adjust the pH to 4.0, stir continuously and homogenize, and then remove bubbles to obtain an AL-PVA / KGM mixed solution.

[0053] (2) The AL-PVA / KGM mixed solution described in (1) is dried into a film as a color development layer by electrospinning. The electrospinning conditions are: No. 21 needle, flow rate of 0.2 mL / min, and aluminum foil paper as the spindle fiber receiving layer. After removing the base film, the AL-PVA-KGM indicator film is obtained.

[0054] The PVA-KGM-AL meat freshness visualization nano-intelligent indicator film prepared in this embodiment is pale yellow and lacks moisture-proof properties. The freshness indicator color of this film ranges from pale yellow to crimson. This indicator film is easily wetted by juices from the meat surface. Being transparent and adhering to the meat surface, it uses the meat surface color as a background, making color changes difficult to observe.

[0055] Example 5

[0056] (1) Dissolve 7 wt% poly-3-hydroxybutyric acid-co-oxyvitamin (PHBV) and ferulic acid in chloroform and stir at 55°C for 2 h to obtain PH-F solution;

[0057] (2) The PH-F solution described in (1) is electrospun and dried. The electrospinning conditions are: No. 22 needle, flow rate of 0.2 mL / min, and aluminum foil is used as the spindle fiber receiving layer. Finally, the base film is removed to obtain the PH-F film as the antibacterial layer.

[0058] (3) Mix 8 wt% polyvinyl alcohol (PVA) and 2 wt% konjac glucomannan (KGM) and dissolve at 90°C for 2-3 hours. After cooling, a PVA / KGM mixed solution is obtained. Add 1 mg / mL alizarin (AL) to the above PVA / KGM mixed solution, adjust the pH to 4.0, stir continuously and homogenize, and then remove bubbles to obtain an AL-PVA / KGM mixed solution.

[0059] (4) The AL-PVA / KGM mixed solution described in (3) is collected on aluminum foil using electrospinning technology to serve as a color development layer, thus obtaining the PVA-KGM-AL preservation indicator film. The electrospinning conditions are: No. 21 needle, flow rate of 0.2 mL / min.

[0060] (5) Overlap the PH-F film with the PVA-KGM-AL preservation indicator film to obtain a P / P double layer film.

[0061] The double-layer film prepared in this embodiment is bonded together by air pressure on both sides. The bond between the two layers is not tight or strong, and gaps exist in the middle. During use, the P / P double-layer film is easily separated or damaged by external factors, causing the inner or outer film to lose its function first, thus rendering the smart preservation indicator function incomplete.

[0062] Example 6 – Case Study of Gelatin and Potassium Sorbate

[0063] A 12 wt% gelatin spinning solution was prepared, and potassium sorbate was dissolved in it as an antibacterial agent. Under conditions of a 13 cm distance between the receiving plate and the needle, a DC voltage of 15 kV, and a feed rate of 0.005 mL / min, the gelatin was spun and collected. The base film was removed to obtain a gelatin-potassium sorbate nanofilm (Gel-K membrane). Gelatin is a natural polymer material derived from the hydrolysis of collagen in animal bodies, possessing excellent biocompatibility and biodegradability. Therefore, gelatin has a wide range of applications in production and daily life. The gelatin antibacterial nanofilm prepared in this embodiment exhibits excellent properties and good antibacterial activity, making it valuable for application in food packaging.

[0064] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization, characterized in that, Includes the following steps: (1) Dissolve PHBV and ferulic acid to obtain a pH-F solution; (2) The PH-F solution was dried by electrospinning and the fibers were collected on aluminum foil to obtain a PH-F film as an antibacterial layer; (3) Mix polyvinyl alcohol (PVA) and konjac glucomannan (KGM) to obtain a polyvinyl alcohol-konjac glucomannan mixed solution; add alizarin to the above mixed solution, adjust the pH and continue mixing and homogenizing, and then remove bubbles to obtain a polyvinyl alcohol-konjac glucomannan-alizarin mixed solution. (4) The polyvinyl alcohol-konjac glucomannan-alizarin mixed solution was coated onto the PH-F membrane again by electrospinning technology as a color development layer. The base film was removed to obtain the PVA-KGM-AL@PH-F double-layer indicator membrane.

2. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The indicator membrane is a double-layer composite membrane. The lower layer is a PHBV-bound ferulic acid layer as an antibacterial layer, and the upper layer is a composite membrane of polyvinyl alcohol (PVA) and konjac glucomannan (KGM), with alizarin embedded as a color development layer.

3. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The preparation method of the PH-F solution includes: mixing PHBV and ferulic acid in chloroform solution, stirring at 50-70°C for 2 hours, and cooling before use.

4. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The substrate of the antibacterial layer is PHBV, with ferulic acid as the antibacterial agent and chloroform solution as the solvent. The concentration of PHBV is 5-7 wt%.

5. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The preparation method of the polyvinyl alcohol-konjac glucomannan mixed solution includes: stirring polyvinyl alcohol (PVA) and konjac glucomannan (KGM) in pure water, stirring at 90°C for 2 hours until completely dissolved, and then letting it cool before use.

6. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The preparation method of the polyvinyl alcohol-konjac glucomannan-alizarin mixed solution includes: adding alizarin to the polyvinyl alcohol-konjac glucomannan mixed solution, adjusting the pH to 4-5, stirring for 5 hours, homogenizing for 2 minutes, and then performing ultrasonic degassing.

7. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The chromogenic layer contains 6-8 wt% PVA, 2 wt% KGM, and 0.5-2 mg / mL alizarin.

8. The method for preparing a nano-intelligent indicator film with dual functions of meat preservation and freshness visualization according to claim 1, characterized in that, The method for preparing the double-layer indicator film includes: covering the antibacterial layer with a color-developing layer and removing the base film to obtain the double-layer preservation indicator film.

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