Dual indication intelligent fresh-keeping label film and preparation method and application thereof

Abstract

This invention belongs to the field of packaging materials and provides a dual-indicator smart preservation label film, its preparation method, and its application. The dual-indicator smart preservation label film includes an antibacterial fluorescent monitoring layer and a colorimetric response layer sequentially stacked along its thickness direction. The antibacterial fluorescent monitoring layer includes a first substrate layer and antibacterial nanoparticles and fluorescent nanoparticles bonded to the first substrate layer. The antibacterial nanoparticles include cinnamaldehyde and β-cyclodextrin encapsulating the cinnamaldehyde, and the fluorescent nanoparticles are supramolecular assemblies synthesized by association-induced synthesis of sulfobutyl β-cyclodextrin and berberine. The colorimetric response layer includes a second substrate layer and alizarin loaded on the second substrate layer. The dual-indicator smart preservation label film provided by this invention integrates visual monitoring and antibacterial preservation functions and can be widely used in the fields of packaged food or indicating the freshness of meat products.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials, specifically relating to a dual-indication smart food preservation label film, its preparation method, and its application. Background Technology

[0002] Meat products are prone to spoilage during storage due to microbial metabolic activity, primarily manifested by the release of biogenic amines, an increase in pH value, and significant changes in key indicators such as volatile basic nitrogen (TVB-N) and total bacterial count (TV-C), seriously threatening their edible quality and safety. Currently, while conventional testing methods such as sensory evaluation, pH measurement, and TVB-N / TV-C analysis can accurately determine the freshness of meat, they are generally cumbersome, time-consuming, labor-intensive, and reliant on large instruments and specialized experience, making it difficult to meet consumers' needs for real-time and convenient monitoring of meat freshness.

[0003] In recent years, smart labels, as a new type of material that can respond to changes in the packaging environment, have shown potential in the field of meat freshness monitoring. These labels usually reflect the accumulation of spoilage markers such as pH or TVB-N through color or fluorescence changes, thereby providing intuitive freshness information. However, most existing smart label technologies have limited functions and face the following prominent limitations in practical applications: (1) Single indication mode: Most labels rely only on a single colorimetric or fluorescence response mechanism, which is easily affected by environmental interference and is difficult to capture the complex spoilage process comprehensively and reliably; (2) Lack of active preservation function: The existing smart labels are limited to "indicating" spoilage and cannot "intervene" in the spoilage process through active mechanisms such as antibacterial activity, thus failing to effectively extend the shelf life of food; (3) Manufacturing process and cost constraints: Existing labels rely on precious metal nanomaterials or complex synthesis processes, resulting in high costs, poor reproducibility of manufacturing, and potential migration safety risks, which hinder their large-scale application; (4) Insufficient performance of label substrate: The mechanical strength, thermal stability, or storage stability of the existing label substrate are poor, affecting its reliability in actual cold chain or storage and transportation environments.

[0004] Current research discloses the construction of gel tags using ovalbumin and chitosan-anthocyanin complexes, which achieves multi-indicator monitoring but still lacks integrated antibacterial function and has not made breakthroughs in substrate strength and process simplicity. Meanwhile, although existing research discloses the use of natural pigments such as curcumin and gardenia blue, and the preparation of amine-sensitive indicator tags using electrospinning technology, their response signal sensitivity and specificity are limited, making it difficult to accurately capture the weak signals in the early stages of meat spoilage.

[0005] Therefore, there is an urgent need in this field to develop a new type of smart label that can not only improve the accuracy and reliability of monitoring through dual signals of colorimetry and fluorescence, but also integrate long-lasting antibacterial function to extend shelf life. Simultaneously, this new smart label should be based on environmentally friendly and low-cost substrates, constructed using simple and safe manufacturing processes, and ultimately yield a reliable product with high temperature resistance, high mechanical strength, and stable storage performance, truly achieving the goal of integrating intelligent indication and active preservation. Summary of the Invention

[0006] The main objective of this invention is to provide a dual-indication smart food preservation label film, its preparation method, and its application, so as to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0008] The first aspect of the present invention provides a dual-indicator smart preservation label film (Alz / CS / AITF), which includes an antibacterial fluorescent monitoring layer (AITF) and a colorimetric response layer (Alz / CS) stacked sequentially along the thickness direction.

[0009] The antibacterial fluorescence monitoring layer includes a first substrate layer and antibacterial nanoparticles (CEO / β-CD) and fluorescent nanoparticles (Be / SBE-β-CD) bonded to the first substrate layer; the antibacterial nanoparticles include cinnamaldehyde (CEO) and β-cyclodextrin (β-CD) coated with cinnamaldehyde; the fluorescent nanoparticles are supramolecular assemblies synthesized by association-induced synthesis of sulfobutyl β-cyclodextrin (SBE-β-CD) and berberine (Be); the colorimetric response layer includes a second substrate layer and alizarin (Alz) loaded on the second substrate layer.

[0010] A second aspect of the present invention provides a method for preparing the dual-indicator smart preservation label film, comprising:

[0011] Antibacterial nanoparticles were prepared by uniformly encapsulating cinnamaldehyde in β-cyclodextrin using an antisolvent method.

[0012] Sulfobutyl β-cyclodextrin and berberine were subjected to ultrasonic treatment to induce association and synthesize supramolecular assemblies, thereby obtaining fluorescent nanoparticles.

[0013] The first substrate layer is sequentially immersed in a solution containing the antibacterial nanoparticles and a solution containing the fluorescent nanoparticles, thereby sequentially adsorbing the antibacterial nanoparticles and the fluorescent nanoparticles to obtain an antibacterial fluorescent monitoring layer.

[0014] A colorimetric response layer mixture containing alizarin, chitosan (CS), and plasticizer is cast onto the surface of the antibacterial fluorescent monitoring layer using a casting process. The antibacterial fluorescent monitoring layer is then combined with the alizarin-chitosan layer to create a dual-indicator smart food preservation film.

[0015] A third aspect of the invention provides the application of the dual-indication smart preservation label film in indicating the freshness of meat products or packaged foods.

[0016] A fourth aspect of the present invention provides a method for indicating the freshness of meat products, comprising using the dual-indication smart preservation label film to test the freshness of the meat product to be tested.

[0017] A fifth aspect of the present invention provides a method for visual monitoring and antibacterial preservation of food, comprising: encapsulating food within a packaging structure and embedding the dual-indicator smart preservation label film within the packaging structure.

[0018] Compared with the prior art, the technical solution of the present invention has at least the following advantages:

[0019] (1) The dual-indicator smart preservation label film provided by the present invention uses cellulose and chitosan as two substrates with opposite charges, respectively loaded with antibacterial substances and functional substances such as fluorescent berberine, as well as colorimetric alizarin, and is compounded by electrostatic interaction to form a double-layer smart label film, which has the characteristics of convenience, low cost, colorimetric / fluorescent dual signal monitoring and active antibacterial preservation.

[0020] (2) Compared with traditional single pH-responsive labels, the dual-indicator smart preservation label film of the present invention adds fluorescent signal indication and cinnamaldehyde antibacterial function, and has significant innovation in structural design and functional integration. The cellulose layer exhibits good adsorption and loading capacity, and the chitosan layer has excellent hydrophobicity and stability, showing good application effect in the actual monitoring and preservation of fresh meat and meat products.

[0021] (3) The dual-indicator smart preservation label film provided by the present invention can achieve intelligent long-term preservation, safe use, low cost and no need for large equipment. Moreover, it integrates visual monitoring and antibacterial preservation functions and has a wide application prospect in the field of packaged food. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a morphological image of the dual-indicator smart food preservation label film prepared in Example 1 of the present invention under natural light.

[0024] Figure 2 The image shows the appearance morphology of the dual-indicator smart food preservation label film prepared in Example 1 of this invention under 365nm ultraviolet light.

[0025] Figure 3a This is a sample image of the dual-indicator smart food preservation label film prepared in Example 1 of the present invention under normal conditions;

[0026] Figure 3b This is a diagram showing the mechanical compliance of the dual-indicator smart food preservation label film prepared in Embodiment 1 of the present invention under bending deformation;

[0027] Figure 4a This is a sample image of the dual-indicator smart food preservation label film prepared in Example 1 of the present invention in its unstretched state;

[0028] Figure 4b This is a diagram showing the deformation state of the dual-indicator smart food preservation label film prepared in Embodiment 1 of the present invention under external force during the stretching process;

[0029] Figure 4c This is a topographic image of the dual-indicator smart food preservation label film prepared in Example 1 of the present invention when stretched to break.

[0030] Figure 5 The color changes of Alz in different pH buffer solutions and their corresponding UV-Vis absorption spectra are shown in the figure.

[0031] Figure 6 The fluorescence emission spectra of Be / SBE-β-CD for ammonia water of different concentrations are shown below.

[0032] Figure 7 The thermal stability diagrams are for the AITF of this invention, the Alz / CS / AITF of Example 1, the CEO / β-CD / CF and the Alz / Cs film;

[0033] Figure 8 The mechanical properties of the CS, AITF and Alz / CS / AITF membranes of Example 1 of the present invention are shown in the diagram.

[0034] Figure 9 This is a color stability diagram of the dual-indicator smart preservation label film prepared in Example 1 of the present invention during storage;

[0035] Figure 10 The cumulative release curves of cinnamaldehyde and berberine during storage of the dual-indicator smart preservation label film prepared in Example 1 of the present invention are shown.

[0036] Figure 11The colorimetric changes of the dual-indicator smart preservation label film prepared in Example 1 of the present invention during the 10-day storage of fresh mutton, fresh prepared mutton, and cooked mutton.

[0037] Figure 12 The image shows the fluorescence changes of the dual-indicator smart preservation label film prepared in Example 1 of the present invention during the 10-day storage of fresh mutton, fresh prepared mutton, and cooked mutton.

[0038] Figure 13 This is a monitoring chart of the freshness of fresh mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0039] Figure 14 The graph shows the determination of volatile basic nitrogen (TVB-N) in fresh mutton using the dual-indicator smart preservation label film prepared in Example 1 of this invention.

[0040] Figure 15 The graph shows the determination of total viable bacteria (TV-C) in fresh mutton using the dual-indicator smart preservation label film prepared in Example 1 of this invention.

[0041] Figure 16 This is a monitoring chart of the freshness of prepared mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0042] Figure 17 This is a TVB-N measurement chart of fresh prepared mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0043] Figure 18 This is a TV-C measurement chart of fresh prepared mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0044] Figure 19 This is a graph showing the freshness monitoring of cooked mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0045] Figure 20 This is a measurement chart of TVB-N in cooked mutton using the dual-indicator smart preservation label film prepared in Example 1 of the present invention.

[0046] Figure 21 This is a TV-C measurement chart of cooked mutton obtained by the dual-indicator smart preservation label film prepared in Example 1 of the present invention. Detailed Implementation

[0047] The invention will be more fully understood by reading the following detailed description. However, it should be understood that the detailed description disclosed below is merely exemplary of the invention, which can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as a representative basis for teaching those skilled in the art to employ the invention in different ways in any suitable detailed embodiment.

[0048] The first aspect of the present invention provides a dual-indication smart preservation label film, comprising an antibacterial fluorescent monitoring layer and a colorimetric response layer sequentially stacked along the thickness direction;

[0049] The antibacterial fluorescent monitoring layer includes a first substrate layer and antibacterial nanoparticles and fluorescent nanoparticles bonded to the first substrate layer; the antibacterial nanoparticles include cinnamaldehyde and β-cyclodextrin encapsulating the cinnamaldehyde; the fluorescent nanoparticles are supramolecular assemblies synthesized by association-induced synthesis of sulfobutyl β-cyclodextrin and berberine; the colorimetric response layer includes a second substrate layer and alizarin loaded on the second substrate layer.

[0050] In this invention, antibacterial nanoparticles can be used to achieve long-lasting antibacterial effects, fluorescent nanoparticles can be used for fluorescence signal indication, and alizarin can be used for pH-responsive colorimetry.

[0051] In some embodiments, the first substrate layer is composed of anionic cellulose and is negatively charged.

[0052] In some embodiments, the first substrate layer has a dense network structure, which is beneficial for the adsorption of antibacterial nanoparticles and fluorescent nanoparticles.

[0053] In some embodiments, the second substrate layer is composed of cationic chitosan and is positively charged. That is, the CS layer is positively charged and the CF substrate layer is negatively charged. According to the principle of electrostatic interaction, this facilitates the formation of a dual-indication smart food preservation label film.

[0054] In this invention, the alizarin is a pH-responsive natural plant extract.

[0055] In some embodiments, the thickness of the antibacterial fluorescent monitoring layer is 0.145~0.165 mm, and the thickness of the colorimetric response layer is 0.06~0.08 mm.

[0056] In some embodiments, the thickness of the first substrate layer is 0.135~0.145 mm.

[0057] In some embodiments, the antibacterial nanoparticles have a diameter of 15,000 to 35,000 nm, and the fluorescent nanoparticles have a diameter of 500 to 800 nm.

[0058] In some embodiments, the antibacterial nanoparticles in the antibacterial fluorescent monitoring layer have a mass fraction of 34-44 wt%, and the fluorescent nanoparticles have a mass fraction of 14-24 wt%.

[0059] In some embodiments, the mass fraction of alizarin in the colorimetric response layer is 1-2 wt%.

[0060] A second aspect of the present invention provides a method for preparing the dual-indicator smart preservation label film, comprising:

[0061] Antibacterial nanoparticles were prepared by uniformly encapsulating cinnamaldehyde in β-cyclodextrin using an antisolvent method.

[0062] Sulfobutyl β-cyclodextrin and berberine were subjected to ultrasonic treatment to induce association and synthesize supramolecular assemblies, thereby obtaining fluorescent nanoparticles.

[0063] The first substrate layer is sequentially immersed in a solution containing the antibacterial nanoparticles and a solution containing the fluorescent nanoparticles, thereby sequentially adsorbing the antibacterial nanoparticles and the fluorescent nanoparticles to obtain an antibacterial fluorescent monitoring layer.

[0064] A colorimetric response layer mixture containing alizarin, chitosan, and plasticizer is cast onto the surface of the antibacterial fluorescent monitoring layer using a casting process. The antibacterial fluorescent monitoring layer is then combined with the alizarin-chitosan layer to create a dual-indicator smart food preservation film.

[0065] In some embodiments, the preparation method specifically includes: mixing an aqueous solution of β-cyclodextrin with an ethanolic solution of cinnamaldehyde at 20-25°C for 5-10 minutes to obtain an antibacterial nanoparticle solution. In this invention, CEO is used as the antibacterial component, and it is encapsulated in β-CD using an antisolvent method to achieve a sustained-release antibacterial effect.

[0066] Furthermore, the molar concentration of the β-cyclodextrin aqueous solution is (4.0~5.0)×10⁻⁶. -3 mol / L.

[0067] Furthermore, the molar concentration of the cinnamaldehyde ethanol solution is 0.30~0.40 mol / L.

[0068] Furthermore, the molar ratio of β-cyclodextrin to cinnamaldehyde is 1:(5.0~6.0).

[0069] In some embodiments, the preparation method specifically includes: mixing an aqueous solution of sulfonyl β-cyclodextrin with an aqueous solution of berberine at 20-25°C for 3-5 minutes, followed by ultrasonic treatment to promote the formation of the supramolecular assembly, thereby obtaining a fluorescent nanoparticle solution. In this step, Be exhibits a high affinity for SBE-β-CD with 10 sulfonyl ether arms, and the strong 1:1 association induces enhanced fluorescence intensity.

[0070] Furthermore, the molar concentration of the sulfobutyl β-cyclodextrin aqueous solution is (6.0~7.0)×10⁻⁶. -3 mol / L mol / L.

[0071] Furthermore, the molar concentration of the berberine aqueous solution is (0.9~1.1)×10⁻⁶. -2 mol / L mol / L.

[0072] Furthermore, the molar ratio of sulfobutyl β-cyclodextrin to berberine is (1.3~1.6).

[0073] Furthermore, the ultrasonic treatment time is 25-35 minutes.

[0074] In some embodiments, the preparation method specifically includes: immersing a first substrate layer (anionic cellulose matrix) in the antibacterial nanoparticle solution and drying it, then immersing it in the fluorescent nanoparticle solution and drying it, repeating the immersion-drying process 1 to 3 times to obtain the antibacterial fluorescent monitoring layer.

[0075] In some embodiments, the preparation method specifically includes: mixing alizarin suspension, chitosan acetic acid solution, and plasticizer evenly to obtain the colorimetric response layer mixed solution, and then casting it onto the surface of the antibacterial fluorescent monitoring layer to obtain a dual-indicator smart preservation film.

[0076] Furthermore, the molar concentration of the alizarin suspension is (3.0~3.5)×10⁻⁶. -2 mol / L.

[0077] Furthermore, the molar concentration of the chitosan acetic acid solution is 0.15~0.18 mol / L.

[0078] Furthermore, the molar ratio of alizarin, chitosan and plasticizer is 1:(140~160):(70~90).

[0079] Furthermore, the plasticizer includes, but is not limited to, glycerin.

[0080] In some more specific embodiments, the preparation method specifically includes the following steps:

[0081] S1. Preparation of antibacterial nanoparticle solution: β-cyclodextrin (β-CD) was dissolved in distilled water at room temperature and stirred at 350 rpm for 60 minutes using a magnetic stirrer to obtain solution A with a molar concentration of (4.0~5.0)×10⁻⁶. -3 Next, cinnamaldehyde (CEO) was dissolved in anhydrous ethanol to obtain solution B, with a molar concentration of 0.30~0.40 mol / L. Solution B was added dropwise to solution A (350 rpm) under continuous stirring. The molar ratio of β-cyclodextrin to cinnamaldehyde was 1:(5.0~6.0). The mixture was stirred at 20~25℃ for 5~10 min to obtain an antibacterial nanoparticle solution (CEO / β-CD).

[0082] S2. Preparation of fluorescent nanoparticle solution: Prepare (6.0~7.0)×10⁻⁶ solution at room temperature. -3 mol / L sulfonyl β-cyclodextrin (SBE-β-CD) aqueous solution and (0.9~1.1)×10 -2 A mol / L berberine (Be) aqueous solution was prepared and mixed thoroughly at 20-25℃ for 3-5 min, wherein the molar ratio of sulfobutyl β-cyclodextrin to berberine was 1:(1.3-1.6). The mixture was then placed in an ultrasonic cleaner to promote the formation of supramolecular assemblies for 25-35 min to obtain a fluorescent nanoparticle solution (Be / SBE-β-CD).

[0083] S3. Preparation of antibacterial fluorescent monitoring layer: A circular cellulose (CF) substrate with a diameter of 90 mm (i.e., the first substrate layer) is immersed in 50 mL of antibacterial nanoparticle solution and then dried in an oven at 35 °C to obtain CEO / β-CD / CF (CFP). Then, it is immersed in fluorescent nanoparticle solution and dried again. The above immersion-drying operation is repeated 3 times. Finally, after drying, a cellulose tag film (AITF) with antibacterial and fluorescent response functions is obtained. The diameter of the antibacterial nanoparticles is about 15,000~35,000 nm, and the diameter of the fluorescent nanoparticles is about 500~800 nm.

[0084] S4. Preparation of colorimetric response layer: Alizarin (Alz) was dispersed in distilled water to prepare an Alz suspension with a molar concentration of (3.0~3.5)×10⁻⁶. -2 mol / L. Separately, chitosan (CS) was dissolved in 1% acetic acid, with a molar concentration of 0.15~0.18 mol / L. The solution was gently stirred for 5 h, and then Alz suspension was added. Glycerin was added as a plasticizer. The molar ratio of alizarin, chitosan and plasticizer was 1:(140~160):(70~90). The solution was stirred vigorously at 25 ℃ for 1 h. After removing air bubbles by sonication, the colorimetric response layer solution (Alz / CS) was obtained.

[0085] S5. Preparation of dual-indicator smart preservation label film: Place a circular antibacterial label film with a diameter of 90 mm at the bottom of a petri dish with a diameter of 100 mm, pour the colorimetric response layer solution onto the surface of the antibacterial fluorescent monitoring layer, and dry it in an oven at 25 ℃ for 12 h to obtain a dual-indicator smart preservation label film (Alz / CS / AITF).

[0086] A third aspect of the invention provides the application of the dual-indication smart preservation label film in indicating the freshness of meat products or packaged foods.

[0087] Furthermore, the meat products include at least one of fresh meat, fresh prepared meat, cooked meat, etc., but are not limited to this.

[0088] In some implementations, the dual-indicator smart preservation label film is stored with the meat at a temperature of 4–30°C to reflect the freshness of the meat; as the amount of volatile biogenic amines in the meat increases, its freshness is determined based on color and fluorescence intensity. When the meat is not fresh, the fluorescence is blue; when the meat is fresh, the fluorescence is green / blue-green.

[0089] A fourth aspect of the present invention provides a method for indicating the freshness of meat products, comprising using the dual-indication smart preservation label film to test the freshness of the meat product to be tested.

[0090] Specifically, when fluorescent nanoparticles respond to volatile amines and are used for meat spoilage monitoring, the presence of large amounts of cationic biogenic amines leads to the substitution of Be in sulfobutyl β-CD, resulting in weakened fluorescence intensity. Antibacterial nanoparticles can provide sustained functional release at different stages, with cinnamaldehyde maintaining long-term antibacterial activity. A pH-responsive hydrophobic colorimetric layer was created using cationic chitosan-loaded alizarin.

[0091] Moreover, when using the dual-indicator smart preservation label film, the CF layer faces inward towards the meat sample, which has good adsorption properties and helps with the adsorption of volatile amines and the slow release of CEO in antibacterial nanoparticles. The CS layer faces outward, which has good hydrophobicity and helps to observe and record color changes.

[0092] A fifth aspect of the present invention provides a method for visual monitoring and antibacterial preservation of food, comprising: encapsulating food within a packaging structure, and embedding the dual-indicator intelligent preservation label film within the packaging structure. This dual-indicator intelligent preservation label film can release antibacterial substances as needed according to the food spoilage pattern, achieving intelligent and long-lasting preservation of the food.

[0093] In summary, this invention provides a dual-indicator smart preservation label film suitable for real-time monitoring of the freshness and shelf-life extension of fresh meat, fresh processed meat, and cooked meat products. This smart preservation label integrates visual monitoring and antibacterial preservation functions. It uses cellulose as the main substrate for the antibacterial monitoring layer and chitosan as the main substrate for the colorimetric response layer. It integrates the antibacterial properties of cinnamaldehyde / β-cyclodextrin nanoparticle solution, alizarin colorimetry, and the fluorescence response characteristics of berberine / sulfobutyl-β-cyclodextrin supramolecular assemblies, constructing a smart label that is heat-resistant, mechanically strong, and has stable storage performance. This smart label can release antibacterial substances as needed according to the food spoilage pattern, achieving intelligent long-term preservation. It is low-cost, simple to prepare, and environmentally friendly, and has broad application prospects in the food packaging field.

[0094] The present invention is further illustrated below by way of examples, but these examples do not limit the invention to the scope of the embodiments described. All reagents and raw materials used in the following examples are commercially available, and test methods not specifically specified are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers. Exemplary examples of the reagents, equipment, and test methods used in the present invention are as follows:

[0095] (a) Reagents used in this invention

[0096] The fresh mutton was purchased from RT-Mart supermarket in Hefei.

[0097] Alizarin, chitosan, glycerin, berberine, cellulose filter paper, and cinnamaldehyde essential oil were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0098] β-Cyclodextrin and sulfobutyl-β-cyclodextrin were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0099] Ammonia, sodium hydroxide, and ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0100] Distilled water was prepared in the laboratory.

[0101] (ii) Equipment used in this invention

[0102] The digital display constant temperature water bath (HH-2) was purchased from Jincheng Guosheng Experimental Instrument Factory in Jintan City, Jiangsu Province.

[0103] The electronic balance (BSA124S) was purchased from Sartorius Scientific Instruments Ltd.

[0104] The freezer (BC / BD-241GSe) was purchased from Qingdao Haier Group;

[0105] The physical property tester (TA-XTplus) was purchased from STable Micro Systems, UK.

[0106] The pH meter (PHS-3C) was purchased from Shanghai Leici Instrument Factory;

[0107] The vacuum freeze dryer (BK-FD10P) was purchased from Shandong Boke Scientific Instruments Co., Ltd.

[0108] The high-speed refrigerated centrifuge (H1650R) was purchased from Beijing Shidai Beili Centrifuge Co., Ltd.

[0109] The handheld colorimeter (NR200) ​​was purchased from Shenzhen 3NH Technology Co., Ltd.

[0110] (III) Test methods in this invention

[0111] 1. pH response of alizarin

[0112] Dissolve 0.1 g of Alz powder in 100 mL of distilled water, and use a spectrophotometer to measure the spectrum of alizarin solution at various pH values ​​(2-13) in the range of 400-800 nm.

[0113] 2. Ammonia response of fluorescent nanoparticles Be / SBE-β-CD

[0114] The Be / SBE-β-CD solution was dispensed into ten 20 mL headspace vials, and ammonia solutions with concentrations of 0 mol / L, 1.5 mol / L, 3 mol / L, 4.5 mol / L, 6 mol / L, 6.5 mol / L, 8 mol / L, 9.5 mol / L, 11 mol / L, and 12.5 mol / L were added dropwise. Using a fluorescence spectrophotometer, the sample solution was added to a 1 mL cuvette, the excitation wavelength was set to 382 nm, and the spectral acquisition range was 450–700 nm.

[0115] 3. Label film performance testing

[0116] (1) Thermal stability test: The vacuum-dried sample was subjected to thermogravimetric analysis in a nitrogen atmosphere. The temperature range was set to 30~600 ℃ and the heating rate was 10 ℃ / min.

[0117] (2) Mechanical property testing: The thickness of the film was measured using a handheld electronic digital micrometer. According to ASTM D882-00, the tensile strength (TS) and elongation at break (EB) of the film were tested using a physical property testing instrument. The sample was cut into rectangular specimens of 50 mm (length) × 20 mm (width), with an initial clamping distance of 30 mm, and a tensile test was performed at a constant rate of 0.6 mm / s. The formulas for calculating TS and EB are as follows:

[0118]

[0119]

[0120] Where F represents the tensile force experienced when the indicator diaphragm breaks, in N; and A represents the cross-sectional area of ​​the indicator diaphragm, in mm². 2 ΔL represents the tensile length of the indicator membrane when it breaks, in mm; L0 represents the initial length of the indicator membrane, in mm.

[0121] (3) Color stability test: The dual-layer smart label film (Alz / CS / AITF) was stored at 4 ℃ and -20 ℃ for 6 days, respectively, and the colorimetric parameters of the label film were collected using a color analyzer. The time of image acquisition, sample position, and lighting remained unchanged. To evaluate the color stability of the label film, the label film samples were stored in environments of 4 ℃ and 25 ℃, and the color change was measured every 5 days. The color difference value (ΔE value) was used to describe its color characteristics, and the test was conducted continuously for 15 days. The formula for calculating ΔE is as follows:

[0122]

[0123] Where ΔL is L-L0; Δa is a-a0; Δb is b-b0; L0, a0, and b0 are the initial color values ​​of the indicator film; L, a, and b are the chromaticity values ​​of the indicator film after illumination.

[0124] (4) Determination of the release rate of cinnamaldehyde essential oil and berberine in the label film

[0125] 10 mL of CEO / β-CD and Be / SBE-β-CD solutions were added dropwise to petri dishes containing cellulose substrate, and then placed in a 40°C oven for 6 hours to load the membrane. After removal, the membrane was cut into 1.5 cm × 1.5 cm square samples, suspended from the top of a 50 mL centrifuge tube, and 20 g of meat sample was placed at the bottom of the tube before sealing. The centrifuge tube was stored at room temperature in the dark. The membranes were removed on days 0, 2, 4, 6, 8, and 10, dried in a 40°C oven to constant weight, and weighed. The cumulative release of CEO and BE was calculated by measuring the mass loss of the membranes at each time point.

[0126] 3. Preparation of processed mutton samples

[0127] After removing the surface fat and fascia from the lamb leg meat, cut it into small pieces of about 5g each, parallel to the muscle fibers. Then, pour the meat pieces and marinade into a vacuum tumbler and tumble for 1 hour. The marinade recipe is as follows: per 100g of marinade, there are 1.8g of edible salt, 1.8g of potassium chloride, 0.8g of five-spice powder, 0.35g of sodium pyrophosphate, 30g of spice water, and 3g of white wine.

[0128] 4. Preparation of boiled mutton samples

[0129] After removing the surface fat and tendons from the lamb leg meat, cut it into small pieces of about 5g each, parallel to the muscle fibers. Place the cut meat pieces in water and heat at a simmer for 30 minutes. Once cooked, remove the meat, drain, and let it cool to room temperature before use.

[0130] 5. Freshness monitoring of raw mutton, raw prepared mutton, and cooked mutton.

[0131] Select 20 g of fresh mutton, fresh prepared mutton, and cooked mutton and place them in a transparent glass container with a volume of 70 cm × 40 cm. Cut the label film into 3 cm × 3 cm pieces and stick them on the inside of the transparent glass lid (cellulose layer facing the meat sample). Set up 3 parallel samples for each group. Do not stick the label film on the glass container in the blank group.

[0132] 6. Determination of volatile basic nitrogen (TVB-N) in meat samples

[0133] Mix 5 g of meat sample with 50 mL of distilled water and stir vigorously. After filtering the mixture, distill the volatile basic nitrogen from the mutton sample using a distillation apparatus. Absorb the evaporated nitrogen with boric acid solution, and then titrate with standard hydrochloric acid titrant. Use the following formula (4) as follows.

[0134]

[0135] Where X represents the TVB-N content (mg / 100g) in the sample; V m This indicates the volume (mL) of standard hydrochloric acid or sulfuric acid titrant consumed by the test solution; V n The reagent blank consumption represents the volume (mL) of hydrochloric acid or sulfuric acid standard titrant; where c represents the concentration (mol / L) of the hydrochloric acid or sulfuric acid standard titrant; 14 represents the equivalence of titrating 1.0 mL of hydrochloric acid [c(HCl) = 1.000mol / L] = standard titrant mass (g / mol) to nitrogen; m represents the sample mass (g); V represents the volume (mL) of accurately absorbed filtrate, in this method V = 10; V0 represents the total volume (mL) of the sample solution, in this method V0 = 100; 100 represents the conversion factor for converting the calculation result to mg / 100g.

[0136] 7. Determination of total viable bacterial count (TV-C) in meat samples

[0137] After mincing 5 g of meat sample, transfer it to a sterile beater bag and homogenize it with 45 mL of sterile physiological saline (0.9% NaCl) at room temperature. Then, dilute it 10-fold with sterile physiological saline to the appropriate concentration. After sterilizing plate counting agar (PCA), pour 15-20 mL aliquots into sterile plastic petri dishes and allow it to solidify. Take 1 mL of each homogenized sample at an appropriate dilution and transfer it to a sterile petri dish using the spread plate method. Incubate the plates at 37℃ ± 1℃ for 48 h, then record the colony count on each plate and calculate the total colony count. Calculate the average value for each treatment using three replicates. The results are expressed as the logarithm of colony forming units (log CFU / g).

[0138] Example 1

[0139] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, specifically including:

[0140] S1. At room temperature, 400 mg of β-cyclodextrin (β-CD) was dissolved in distilled water and stirred at 350 rpm for 60 minutes using a magnetic stirrer to obtain solution A with a molar concentration of 0.00441 mol / L. Next, 0.24 mL of cinnamaldehyde (CEO) was dissolved in 5 mL of anhydrous ethanol to obtain solution B with a molar concentration of 0.381 mol / L. Solution B was added dropwise to solution A (350 rpm) with continuous stirring, at a molar ratio of β-cyclodextrin to cinnamaldehyde of 1:5.4. The mixture was stirred at 25°C for 5 minutes to obtain an antibacterial nanoparticle solution (CEO / β-CD). The diameter of the antibacterial nanoparticles was approximately 24207 ± 6217 nm.

[0141] S2. Prepare an aqueous solution of 0.00656 mol / L sulfobutyl β-cyclodextrin (SBE-β-CD) and a solution of 0.01 mol / L berberine (Be) at room temperature, and mix them thoroughly at 25°C for 3 min. The molar ratio of sulfobutyl β-cyclodextrin to berberine is 1:1.52. Place the mixture in an ultrasonic cleaner to promote the formation of supramolecular assemblies for 30 min to obtain a fluorescent nanoparticle solution (Be / SBE-β-CD). The diameter of the fluorescent nanoparticles is approximately 649 ± 105 nm.

[0142] S3. Preparation of antibacterial fluorescent monitoring layer: A circular cellulose (CF) substrate with a diameter of 90 mm (thickness of about 0.137 mm) was soaked in 50 mL of antibacterial nanoparticle solution and then dried in an oven at 35 ℃ to obtain CEO / β-CD / CF (CFP). Then, it was soaked in fluorescent nanoparticle solution and dried again. The above soaking-drying operation was repeated 3 times. Finally, the antibacterial fluorescent monitoring layer (AITF) was obtained after drying.

[0143] S4. Preparation of the colorimetric response layer: 40 mg alizarin (Alz) was dispersed in 5 mL of distilled water to prepare an Alz suspension with a molar concentration of 0.0333 mol / L. Separately, 4 g of chitosan (CS) was dissolved in 150 mL of 1% acetic acid with a molar concentration of 0.165 mol / L. The mixture was gently stirred for 5 h, and then the Alz suspension was added, along with 1.2 g of glycerol as a plasticizer. The molar ratio of alizarin, chitosan, and plasticizer was 1:148:78. The mixture was vigorously stirred at 25 ℃ for 1 h, and after ultrasonic removal of air bubbles, the colorimetric response layer solution (Alz / CS) was obtained.

[0144] S5. Preparation of dual-indicator smart preservation label film: Place a circular antibacterial fluorescent label film with a diameter of 90 mm at the bottom of a petri dish with a diameter of 100 mm, pour 25 mL of colorimetric response layer solution onto the top layer, and dry in an oven at 25 ℃ for 12 h to obtain the dual-indicator smart preservation label film (Alz / CS / AITF).

[0145] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.22 mm, wherein the thickness of the antibacterial fluorescent monitoring layer is approximately 0.152 mm, the thickness of the colorimetric response layer is approximately 0.07 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 39 wt%, the mass fraction of fluorescent nanoparticles is approximately 19 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1.4 wt%.

[0146] Figure 1 This is a morphological image of the dual-indicator smart food preservation label film prepared in this embodiment under natural light. Figure 2 The image shows the appearance of the dual-indicator smart food preservation label film prepared in this embodiment under 365nm ultraviolet light. Figure 3a This is a sample image of the dual-indicator smart food preservation label film prepared in Example 1 under normal conditions; Figure 3b This is a diagram showing the mechanical compliance of the dual-indicator smart food preservation label film prepared in Example 1 under bending deformation. Figure 4a This is a sample image of the dual-indicator smart food preservation label film prepared in Example 1 in its unstretched state; Figure 4b This is a diagram showing the deformation state of the dual-indicator smart food preservation label film prepared in Example 1 under external force during the stretching process. Figure 4c This is a morphological image of the dual-indicator smart food preservation label film prepared in Example 1 when stretched to break. It can be seen that the dual-indicator smart food preservation label film of this embodiment has good flexibility.

[0147] Example 2

[0148] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0149] The molar concentration of S1, β-cyclodextrin aqueous solution is 4.0 × 10⁻⁶. -3 The molar concentration of cinnamaldehyde ethanol solution was 0.3 mol / L, the molar ratio of β-cyclodextrin to cinnamaldehyde was 1:5, and the mixture was stirred evenly at 20°C for 10 min. The rest of the steps were the same as S1 in Example 1, and the diameter of the antibacterial nanoparticles remained basically unchanged.

[0150] S2 is the same as step S2 in Example 1.

[0151] S3, soaking-drying operation 3 times, circular cellulose (CF) substrate (thickness approximately 0.140 mm), the rest is the same as step S3 of Example 1.

[0152] S4 is the same as step S4 in Example 1.

[0153] S5 is the same as step S5 in Example 1.

[0154] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.215 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.145 mm, the thickness of the colorimetric response layer is approximately 0.07 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 34 wt%, the mass fraction of fluorescent nanoparticles is approximately 19 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1.4 wt%.

[0155] Example 3

[0156] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0157] The molar concentration of S1, β-cyclodextrin aqueous solution is 5 × 10⁻⁶. -3 The molar concentration of cinnamaldehyde ethanol solution was 0.4 mol / L, the molar ratio of β-cyclodextrin to cinnamaldehyde was 1:6, and the mixture was stirred evenly at 23°C for 8 min. The rest of the steps were the same as S1 in Example 1, and the diameter of the antibacterial nanoparticles remained basically unchanged.

[0158] S2 is the same as step S2 in Example 1.

[0159] S3, soaking-drying operation once, circular cellulose (CF) substrate (thickness approximately 0.145 mm), the rest is the same as step S3 of Example 1.

[0160] S4 is the same as step S4 in Example 1.

[0161] S5 is the same as step S5 in Example 1.

[0162] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.235 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.165 mm, the thickness of the colorimetric response layer is approximately 0.07 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 44 wt%, the mass fraction of fluorescent nanoparticles is approximately 19 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1.4 wt%.

[0163] Example 4

[0164] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0165] S1 is the same as step S1 in Example 1.

[0166] The molar concentration of S2, sulfonyl β-cyclodextrin aqueous solution, is 6.0 × 10⁻⁶. -3 The molar concentration of berberine aqueous solution is 0.9 × 10⁻⁶ mol / L. -2 The mol / L sulfobutyl β-cyclodextrin and berberine were mixed at a molar ratio of 1:1.3 at 20°C for 5 min, and the ultrasonic treatment time was 25 min. The rest of the steps were the same as S2 in Example 1, and the diameter of the fluorescent nanoparticles remained basically unchanged.

[0167] S3 is the same as step S3 in Example 1.

[0168] S4 is the same as step S4 in Example 1.

[0169] S5 is the same as step S5 in Example 1.

[0170] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.22 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.149 mm, the thickness of the colorimetric response layer is approximately 0.07 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 39 wt%, the mass fraction of fluorescent nanoparticles is approximately 14 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1.4 wt%.

[0171] Example 5

[0172] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0173] S1 is the same as step S1 in Example 1.

[0174] The molar concentration of S2, sulfonyl β-cyclodextrin aqueous solution, is 7.0 × 10⁻⁶. -3 The molar concentration of berberine aqueous solution is 1.1 × 10⁻⁶ mol / L. -2The mol / L sulfobutyl β-cyclodextrin and berberine were mixed at a molar ratio of 1:1.6 at 22°C for 4 min, and the ultrasonic treatment time was 35 min. The rest of the steps were the same as S2 in Example 1, and the diameter of the fluorescent nanoparticles remained basically unchanged.

[0175] S3 is the same as step S3 in Example 1.

[0176] S4 is the same as step S4 in Example 1.

[0177] S5 is the same as step S5 in Example 1.

[0178] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.23 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.160 mm, the thickness of the colorimetric response layer is approximately 0.07 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 39 wt%, the mass fraction of fluorescent nanoparticles is approximately 24 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1.4 wt%.

[0179] Example 6

[0180] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0181] S1 is the same as step S1 in Example 1.

[0182] S2 is the same as step S2 in Example 1.

[0183] S3 is the same as step S3 in Example 1.

[0184] S4, the molar concentration of alizarin suspension is 3.0 × 10⁻⁶. -2 The molar concentration of the chitosan acetic acid solution was 0.15 mol / L, and the molar ratio of alizarin, chitosan and plasticizer was 1:140:70. The rest was the same as step S4 in Example 1.

[0185] S5 is the same as step S5 in Example 1.

[0186] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.212 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.152 mm, the thickness of the colorimetric response layer is approximately 0.06 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 39 wt%, the mass fraction of fluorescent nanoparticles is approximately 19 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 1 wt%.

[0187] Example 7

[0188] This embodiment provides a method for preparing a dual-indicator smart food preservation label film, which differs from Embodiment 1 in that:

[0189] S1 is the same as step S1 in Example 1.

[0190] S2 is the same as step S2 in Example 1.

[0191] S3 is the same as step S3 in Example 1.

[0192] S4, the molar concentration of alizarin suspension is 3.5 × 10⁻⁶. -2 The molar concentration of the chitosan acetic acid solution was 0.18 mol / L, and the molar ratio of alizarin, chitosan and plasticizer was 1:160:90. The rest was the same as step S4 in Example 1.

[0193] S5 is the same as step S5 in Example 1.

[0194] In this embodiment, the total thickness of the dual-indicator smart preservation label film is approximately 0.232 mm, the thickness of the antibacterial fluorescent monitoring layer is approximately 0.152 mm, the thickness of the colorimetric response layer is approximately 0.08 mm, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is approximately 39 wt%, the mass fraction of fluorescent nanoparticles is approximately 19 wt%, and the mass fraction of alizarin in the colorimetric response layer is approximately 2 wt%.

[0195] Comparative Example 1

[0196] This comparative example provides a cellulose label film (CEO / β-CD / CF) with antibacterial function, and its preparation method is as follows:

[0197] S1 is the same as step S1 in Example 1.

[0198] S2. Immerse a 90 mm diameter circular cellulose (CF) substrate in 50 mL of antibacterial nanoparticle solution and dry it in a 35 ℃ oven. Repeat the above immersion-drying operation 3 times to obtain a cellulose label film (CEO / β-CD / CF) with antibacterial function.

[0199] Comparative Example 2

[0200] This comparative example provides a cellulose tag film (SBE-β-CD-CF) with fluorescence response function, and its preparation method is as follows:

[0201] S1. Prepare an aqueous solution of 0.00656 mol / L sulfobutyl β-cyclodextrin (SBE-β-CD).

[0202] S2. Soak a circular cellulose (CF) substrate with a diameter of 90 mm in 50 mL of SBE-β-CD aqueous solution, and then dry it in an oven at 35 ℃. Repeat the above soaking-drying operation 3 times to obtain a cellulose tag film (SBE-β-CD-CF) with fluorescent response function.

[0203] Comparative Example 3

[0204] This comparative example provides a cellulose label film (Alz / CS-CF) with colorimetric response function, and its preparation method is as follows:

[0205] S1 is the same as step S4 in Example 1.

[0206] S2. Immerse a circular cellulose (CF) substrate with a diameter of 90 mm in 50 mL of colorimetric responsive layer solution (Alz / CS), and then dry it in an oven at 35 ℃. Repeat the above immersion-drying operation 3 times to obtain a cellulose label film (Alz / CS-CF) with colorimetric responsive function.

[0207] Comparative Example 4

[0208] This comparative example provides a cellulose label film (CEO / β-CD-Alz / CS-CF) with antibacterial and colorimetric response functions, and its preparation method is as follows:

[0209] S1 is the same as step S1 in Example 1.

[0210] S2. Immerse a 90 mm diameter circular cellulose (CF) substrate in 50 mL of antibacterial nanoparticle solution and dry it in a 35 ℃ oven. Repeat the above immersion-drying operation 3 times to obtain a cellulose label film (CEO / β-CD / CF) with antibacterial function.

[0211] S3 is the same as step S4 in Example 1.

[0212] S4. Place a 90 mm diameter circular CEO / β-CD / CF membrane at the bottom of a 100 mm diameter petri dish. Pour 25 mL of colorimetric response layer solution onto the surface of the CEO / β-CD / CF membrane and dry it in an oven at 25 ℃ for 12 h to obtain a cellulose label membrane (CEO / β-CD-Alz / CS-CF) with antibacterial and colorimetric response functions.

[0213] Comparative Example 5

[0214] This comparative example provides a Be / SBE-β-CD-Alz / CS-CF membrane, the specific preparation method of which is as follows:

[0215] S1 is the same as step S2 in Example 1.

[0216] S2. Immerse a 90 mm diameter circular cellulose (CF) substrate in 50 mL of fluorescent nanoparticle solution, then dry it in an oven at 35 °C. Repeat the above immersion-drying operation 3 times to obtain a cellulose tag film (Be / SBE-β-CD-CF) with fluorescent response function.

[0217] S3 is the same as step S4 in Example 1.

[0218] S4. Place a 90 mm diameter circular Be / SBE-β-CD-CF membrane at the bottom of a 100 mm diameter culture dish. Pour 25 mL of colorimetric response layer solution onto the surface of the Be / SBE-β-CD-CF membrane and dry it in an oven at 25 ℃ for 12 h to obtain a cellulose tag membrane (CEO / β-CD-Alz / CS-CF) with fluorescence and colorimetric response functions.

[0219] Comparative Example 6

[0220] This comparative example provides a cellulose tag film (CEO / β-CD-Be / SBE-β-CD-CF, i.e., AITF) with a single-layer antibacterial fluorescent monitoring layer, and its preparation method is as follows:

[0221] S1 is the same as step S1 in Example 1.

[0222] S2 is the same as step S2 in Example 1.

[0223] S3. Same as step S3 in Example 1, to prepare a cellulose tag film (AITF) with a single layer of antibacterial fluorescent monitoring layer.

[0224] Test Example 1

[0225] (1) Results and analysis of alizarin pH response:

[0226] To verify the pH-responsive performance of alizarin, this invention tested the color changes of Alz in different pH buffer solutions. For example... Figure 5 As shown, the color of Alz changes from yellow to purple at pH 2 to 13. By increasing the pH value from 2 to 13, the maximum absorption wavelength of Alz shifts from 520 nm to 595 nm, demonstrating excellent pH response performance.

[0227] (2) Ammonia response results and analysis of fluorescent nanoparticles Be / SBE-β-CD:

[0228] like Figure 6 As shown, the bright yellow fluorescence of the nanoparticles gradually weakens with increasing ammonia concentration. This figure demonstrates that fluorescent nanoparticles can serve as an effective fluorescent probe.

[0229] (3) Thermal stability analysis of dual-indicator smart food preservation label film:

[0230] Thermal stability is shown as follows Figure 7 As shown, the initial decomposition temperatures of AITF and CEO / β-CD / CF are both around 280 °C, due to the high melting point of the CF substrate. In contrast, the initial decomposition temperature of Alz / CS is significantly lower than that of AITF and CEO / β-CD / CF, because the melting point of CS is lower than that of CF. The dual-indication smart insurance label film Alz / CS / AITF of this invention has an initial decomposition temperature higher than that of the CS substrate film, and its residue exceeds 20% at 600 °C, which is significantly higher than that of the CF substrate film. The thermal stability results indicate that the complementarity of CF and CS significantly improves the thermal stability of the Alz / CS / AITF label film.

[0231] (4) Mechanical property analysis of dual-indication smart food preservation label film:

[0232] Figure 8 The tensile strength and elongation at break of three membranes—CS, AITF, and Alz / CS / AITF—were demonstrated. The results showed that the Alz / CS / AITF composite membrane had a tensile strength of approximately 45 MPa and an elongation at break of approximately 10%, significantly higher than the single-layer antibacterial fluorescent monitoring tag membrane AITF. This indicates that the composite of CS and CF has a positive effect on tensile strength and elongation at break.

[0233] (5) Color stability analysis of dual-indicator smart food preservation label film:

[0234] like Figure 9 As shown, the ΔE values ​​of the label film after 15 days of storage at 4 ℃ and 25 ℃ were 0.062 and 0.064, respectively, with no significant color change. This indicates that the label film has excellent stability, which is of great significance for monitoring the freshness of meat products.

[0235] (6) Results and analysis of the release of cinnamaldehyde and berberine in dual-indicator smart food preservation label film:

[0236] like Figure 10As shown, both cinnamaldehyde and berberine exhibited a sustained and stable release trend. The release rate of CEO / β-CD gradually increased with storage time, reaching approximately 51.54% by day 10, indicating its good sustained-release properties, which helps achieve long-term antibacterial effects. Meanwhile, the release behavior of Be / SBE-β-CD was more significant, with a cumulative release rate as high as approximately 71.98% by day 10, showing faster release kinetics, which helps establish an effective signal response in the early stages of spoilage. Overall, the results indicate that this label film can provide continuous functional release at different stages, enabling early monitoring through berberine and maintaining long-term antibacterial activity through cinnamaldehyde, meeting the requirements of time-gradient functionality for indication and preservation label films.

[0237] Test Example 2

[0238] Testing the freshness monitoring and actual preservation effect of the dual-indicator smart preservation label film in different mutton samples:

[0239] Throughout the storage period, the label films of all experimental groups exhibited a regular bimodal color change.

[0240] Dual-indicator smart label films were applied to three types of mutton samples: fresh, prepared, and boiled. Their freshness indication and preservation performance during actual storage were systematically evaluated. Colorimetric changes in fresh, prepared, and cooked mutton during 10 days of storage are shown in the following graphs. Figure 11 As shown in the figure, the fluorescence change diagram is as follows: Figure 12 As shown, the label films of all experimental groups exhibited a regular bimodal color change throughout the storage period. Figure 12 The visible color of the membrane gradually changed from an initial yellow to a dark red, while the intensity of its bright yellow fluorescence continuously decreased. This color change trend is consistent with the results of TVB-N and TV-C measurements, jointly confirming that all three types of mutton samples spoiled with prolonged storage.

[0241] In terms of preservation effect, compared with the control group (which did not use the label film), the dual-indicator smart label film of the treatment group showed significant antibacterial and preservation function.

[0242] The dual-indicator smart preservation label film monitors the freshness of fresh lamb as shown in the image. Figure 13 As shown.

[0243] The TVB-N measurement chart of the dual-indicator smart food preservation label film for fresh mutton is shown below. Figure 14 As shown.

[0244] The TV-C measurement chart of the dual-indicator smart food preservation label film for fresh mutton is shown below. Figure 15 As shown.

[0245] The dual-indicator smart preservation label film monitors the freshness of prepared lamb as shown in the image. Figure 16 As shown.

[0246] The TVB-N measurement chart of the dual-indicator smart preservation label film for fresh prepared lamb is shown below. Figure 17 As shown.

[0247] The TV-C measurement chart of the dual-indicator smart preservation label film for fresh prepared lamb is shown below. Figure 18 As shown.

[0248] The dual-indicator smart preservation label film monitors the freshness of cooked mutton as shown in the image. Figure 19 As shown.

[0249] The TVB-N measurement chart for cooked mutton using this dual-indicator smart food preservation label film is shown below. Figure 20 As shown.

[0250] The TV-C measurement chart of cooked lamb using this dual-indicator smart preservation label film is shown below. Figure 21 As shown.

[0251] from Figures 13-21 As can be seen, the dual-indicator smart preservation label film of Embodiment 1 of the present invention extends the shelf life of fresh mutton by approximately 2 days and the shelf life of fresh prepared mutton by approximately 1 day. For cooked mutton, due to its high-temperature cooking process, the initial microbial content is low and the lipid oxidation stability is relatively high, resulting in a slower spoilage rate and a relatively longer storage time; under these conditions, the label film can still effectively extend its shelf life by approximately 20 hours. These results fully demonstrate that the dual-indicator smart label film possesses excellent real-time freshness monitoring capabilities and effective preservation functions in mutton systems processed using different methods.

[0252] Test Example 3

[0253] The dual-indicator smart preservation label film prepared in Examples 1-7 of the present invention and the label film prepared in Comparative Examples 1-6 were subjected to performance tests, and the test results are shown in Table 1.

[0254] Table 1 Performance test results of the label films of Examples 1-7 and Comparative Examples 1-6

[0255]

[0256] As shown in Table 1, different formulations and structural designs significantly affected the mechanical properties, thermal stability, color stability, and preservation effect of the dual-indicator smart preservation label film. Among them, Example 1 showed the most balanced and outstanding comprehensive advantages in all key indicators. First, in terms of mechanical properties, the tensile strength of Example 1 was 45 MPa and the elongation at break was 10%, which was significantly better than that of Comparative Example 1 (32 MPa, 6%), Comparative Example 2 (32 MPa, 5%), and Comparative Example 3 (40 MPa, 8%), which contained only single functional components. This indicates that the ratio of CEO / β-CD, Be / SBE-β-CD, and Alz / CS and the interlayer structure design adopted in Example 1 resulted in a more ideal continuous phase and interfacial bonding state of the film material. While maintaining sufficient mechanical strength, it also took into account flexibility, making it more suitable as a label carrier that can be practically operated and pasted. Secondly, the initial decomposition temperature of Example 1 was 260°C, which was slightly lower than that of Comparative Examples 1, 2 and 6 (340-360°C) containing only cyclodextrin or some functional components, but significantly higher than that of Comparative Example 3 (230°C) containing only a colorimetric layer. This indicates that after the introduction of bifunctional guests and plasticizing systems, the label film still maintained good thermal stability and could fully meet the usage requirements during low-temperature refrigeration and normal-temperature circulation.

[0257] More importantly, Example 1 demonstrated the best performance in terms of optical stability and preservation effect. Its ΔE values ​​after 15 days of storage at 4℃ and 25℃ were 0.062 and 0.064, respectively, both lower than Comparative Examples 3-5 (ΔE of 0.075-0.10) and most other examples. This indicates that before significant spoilage occurs, the label background color difference is minimal, and background drift is negligible, which is beneficial for improving the accuracy of freshness indication in the later stages. Furthermore, under the same storage conditions, Example 1 extended the shelf life of fresh, prepared, and cooked lamb to 5, 6, and 7 days, respectively, a significant improvement of approximately 1-3 days compared to the 3-4 days of Comparative Examples 1-3, and also superior to Comparative Examples 4 and 5, which only introduced single antibacterial or single indicator functions. Considering the comprehensive mechanical properties, thermal stability, color stability, and shelf-life extension effect on fresh, prepared, and cooked lamb, the formulation and structure of Example 1 achieves the optimal synergy among antibacterial, fluorescence monitoring, and colorimetric indication, making it the best-performing implementation scheme in this system. Although the label films of Examples 2-7 have slightly weaker overall performance than those of Example 1, they still have significant technical advantages over the label films of Comparative Examples 1-6.

[0258] All aspects, embodiments, features, and examples of this invention should be considered illustrative in all respects and are not intended to limit the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0259] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0260] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A dual indication smart freshness preserving label film, characterized in that, It includes an antibacterial fluorescence monitoring layer and a colorimetric response layer that are stacked sequentially along the thickness direction; The antibacterial fluorescent monitoring layer includes a first substrate layer and antibacterial nanoparticles and fluorescent nanoparticles bonded to the first substrate layer; the antibacterial nanoparticles include cinnamaldehyde and β-cyclodextrin encapsulating the cinnamaldehyde; the fluorescent nanoparticles are supramolecular assemblies synthesized by association-induced synthesis of sulfobutyl β-cyclodextrin and berberine. The colorimetric response layer includes a second substrate layer and alizarin loaded on the second substrate layer; The first substrate layer is composed of anionic cellulose, and the second substrate layer is composed of cationic chitosan.

2. The dual-indication smart freshness labelling film according to claim 1, characterized in that: The first substrate layer has a dense network structure.

3. The dual-indication smart freshness labelling film according to claim 1, characterized in that: The thickness of the antibacterial fluorescent monitoring layer is 0.145~0.165mm, and the thickness of the colorimetric response layer is 0.06~0.08mm; And / or, the thickness of the first substrate layer is 0.135~0.145mm; And / or, the diameter of the antibacterial nanoparticles is 15000~35000nm, and the diameter of the fluorescent nanoparticles is 500~800nm; And / or, the mass fraction of antibacterial nanoparticles in the antibacterial fluorescent monitoring layer is 34~44wt%, and the mass fraction of fluorescent nanoparticles is 14~24wt%. And / or, the mass fraction of alizarin in the colorimetric response layer is 1~2wt%.

4. The method for preparing the dual-indicator smart food preservation label film as described in any one of claims 1-3, characterized in that, include: Antibacterial nanoparticles were prepared by uniformly encapsulating cinnamaldehyde in β-cyclodextrin using an antisolvent method. Sulfobutyl β-cyclodextrin and berberine were subjected to ultrasonic treatment to induce association and synthesize supramolecular assemblies, thereby obtaining fluorescent nanoparticles. The first substrate layer is sequentially immersed in a solution containing the antibacterial nanoparticles and a solution containing the fluorescent nanoparticles, thereby sequentially adsorbing the antibacterial nanoparticles and the fluorescent nanoparticles to obtain an antibacterial fluorescent monitoring layer. A colorimetric response layer mixture containing alizarin, chitosan, and plasticizer is cast onto the surface of the antibacterial fluorescent monitoring layer using a casting process. The antibacterial fluorescent monitoring layer is then combined with the alizarin-chitosan layer to create a dual-indicator smart food preservation film.

5. The preparation method according to claim 4, characterized in that, Specifically, it includes: Mix β-cyclodextrin aqueous solution and cinnamaldehyde ethanol solution at 20-25℃ for 5-10 min to obtain antibacterial nanoparticle solution; And / or, the preparation method specifically includes: mixing sulfonyl β-cyclodextrin aqueous solution and berberine aqueous solution at 20~25℃ for 3~5 min, and then ultrasonically treating to promote the formation of supramolecular assemblies to obtain fluorescent nanoparticle solution; And / or, the preparation method specifically includes: immersing the first substrate layer in the antibacterial nanoparticle solution, drying it, then immersing it in the fluorescent nanoparticle solution, drying it, and repeating the immersion-drying process 1 to 3 times to obtain the antibacterial fluorescent monitoring layer; And / or, the preparation method specifically includes: mixing alizarin suspension, chitosan acetic acid solution and plasticizer evenly at room temperature to obtain the colorimetric response layer mixed solution, and then casting it onto the surface of the antibacterial fluorescent monitoring layer to obtain a dual-indicator smart preservation film.

6. The preparation method according to claim 5, characterized in that: The molar concentration of the β-cyclodextrin aqueous solution is (4.0~5.0)×10⁻⁶. -3 mol / L; And / or, the molar concentration of the cinnamaldehyde ethanol solution is 0.30~0.40 mol / L; And / or, the molar ratio of the β-cyclodextrin to cinnamaldehyde is 1:(5.0~6.0); And / or, the molar concentration of the sulfobutyl beta-cyclodextrin aqueous solution is (6.0~7.0)×10 -3 mol / L; And / or, the molar concentration of the berberine aqueous solution is (0.9~1.1)×10 -2 mol / L; And / or, the molar ratio of the sulfobutyl β-cyclodextrin to berberine is 1:(1.3~1.6); And / or, the molar concentration of the alizarin suspension is (3.0-3.5) x 10 -2 mol / L. And / or, the molar concentration of the chitosan acetic acid solution is 0.15~0.18 mol / L; And / or, the molar ratio of alizarin, chitosan and plasticizer is 1:(140~160):(70~90); And / or, the duration of the ultrasonic treatment is 25-35 min; And / or, the plasticizer includes glycerin.

7. The application of the dual-indicator smart preservation label film as described in any one of claims 1-3 in indicating the freshness of meat products or packaged foods.

8. Use according to claim 7, characterized in that: The meat products include at least one of fresh meat, fresh prepared meat, and cooked meat.

9. A method of indicating freshness of meat, characterized by, The freshness of the meat product to be tested is verified using the dual-indicator smart preservation label film as described in any one of claims 1-3.

10. A method of food visual monitoring and antibacterial preservation, characterized in that, include: Food is encapsulated within a packaging structure, and a dual-indication smart preservation label film as described in any one of claims 1-3 is embedded within the packaging structure.

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