Intelligent food packaging film for monitoring meat freshness and preparation method thereof

Abstract

The invention provides an intelligent food packaging film for monitoring meat freshness and a preparation method thereof. The packaging film comprises pyracantha fortuneana fruit anthocyanin, a biodegradable polymer matrix and a plasticizer, the biodegradable polymer matrix is a combination of any two of chitosan (CS), starch (ST) and polyvinyl alcohol (PVA); the packaging film has excellent pH response capability and high monitoring sensitivity to ammonia; the packaging film has great application potential in the field of intelligent food packaging, and a new solution is provided for food packaging technology innovation.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, specifically to a smart food packaging film for monitoring the freshness of meat and its preparation method. Background Technology

[0002] Food packaging plays a vital role in the modern food industry, not only maintaining the freshness and nutritional value of food but also ensuring the safe transportation and storage of long-distance global supply chains. The shelf life of food is closely related to its inherent characteristics, the protective effect of packaging materials, and the environmental conditions exposed during transportation and storage. The protection provided by packaging materials is determined by the properties of the materials and the type of packaging structure. Currently, the main research focus in the food packaging field is developing advanced packaging systems with enhanced functional properties and designing and manufacturing food packaging materials with efficient protective functions and intelligent display capabilities. Smart packaging aims to monitor food conditions, understand its status in a timely manner, and interact with food in a controlled and beneficial way. The global smart packaging market was valued at US$14.72 billion in 2019 and is projected to grow to US$26.7 billion by 2026, with a projected compound annual growth rate of 8.8%.

[0003] In response to global sustainable development goals and to reduce environmental impact, biodegradable and renewable polymer materials are increasingly replacing petroleum-based and non-biodegradable food packaging materials. Natural polymers such as chitosan, starch, polyvinyl alcohol, agar, and cellulose possess excellent biocompatibility, safety, non-toxicity, effective film-forming properties, and biodegradability, making them ideal choices for smart food packaging materials. However, single-component materials often have unavoidable problems, such as the relatively weak mechanical properties of chitosan films and the water sensitivity of starch, which limits the widespread application of single-component polymer framework materials in high-performance smart packaging. Therefore, much current research focuses on compounding two or more organic framework materials to overcome the limitations of single-matrix materials. Among these, polyvinyl alcohol, due to its high mechanical strength, non-toxicity, and strong affinity for water, has become a popular choice for blending with natural polymers to manufacture composite materials.

[0004] Smart packaging achieves monitoring functions through indicators and microsensors. Its core principle lies in the fact that indicators react with specific substances produced by food, generating visible color changes and providing real-time insights into freshness. Currently used dyes as food indicators include bromocresol green, phenol red, and thymol blue. These dyes indicate food freshness through different pH reactions; however, they pose potential risks to human health. In recent years, to reduce the risks associated with indicators, the use of natural dyes as indicators has increased. There are many types of natural dyes, such as anthocyanins, curcumin, betaine, and shikonin. Among them, anthocyanins (ACNs) have become one of the best material choices for smart food packaging indicators due to their wide pH color-changing range, safety, non-toxicity, antibacterial properties, and antioxidant effects. Dyes originate from the stems, leaves, flowers, and fruits of plants. Taking anthocyanins as an example, anthocyanins from blueberries, purple sweet potatoes, and roses are commonly used. However, these sources of anthocyanins have limitations in application. For instance, while blueberry anthocyanins have high content, the raw material cost is high, and their extracts often contain a lot of organic acids and sugars. When combined with film-forming matrices (such as chitosan and polyvinyl alcohol) to prepare packaging, they are prone to moisture absorption, leading to decreased mechanical strength and poor stability of the resulting film. Furthermore, pigment leakage or degradation can easily occur during storage. For example, purple sweet potato anthocyanins sometimes do not have a wide enough color response range in alkaline environments, and the transition from red to green is not clear enough, resulting in poor indication. Moreover, as cash crops, the prices and supply stability of both blueberries and purple sweet potatoes are greatly affected by market fluctuations, which is not conducive to cost control in industrial production.

[0005] Pyracantha is an evergreen shrub belonging to the genus Pyracantha in the family Rosaceae. It produces bright red edible berries and is mainly distributed in areas south of the Yellow River and in vast regions of Southwest, Central, and East China in China. It has rich nutritional value, as well as important medicinal and economic value. Its fruit is rich in anthocyanins and various active ingredients, and is widely used in functional foods, antioxidants, and nutritional supplements. Anthocyanins extracted from Pyracantha fruit have excellent antioxidant, antibacterial, and pH-sensitive properties, but there is no record of using them as smart packaging indicators. Therefore, providing a cost-effective and effective Pyracantha anthocyanin smart indicator film is of great significance for biodegradable and smart food packaging. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide an intelligent food packaging film for monitoring meat freshness and its preparation method. The intelligent food packaging film uses a binary blend system composed of any two of starch, polyvinyl alcohol, and chitosan as the organic framework material, adds thorny fruit anthocyanins as a functional component, and adds glycerin as a plasticizer. The film is prepared through mixing, casting, and peeling. The resulting packaging film has the advantages of high and rapid response sensitivity, thus achieving convenient and rapid monitoring of meat freshness. It can effectively monitor the freshness of meat during storage, transportation, and sales. The packaging film uses natural extracts, which are environmentally friendly and pollution-free, meeting the requirements of modern food packaging.

[0007] The technical solution of the present invention is as follows: A smart food packaging film for monitoring meat freshness includes firethorn fruit anthocyanins (G-ATH), a biodegradable polymer matrix, and a plasticizer; The biodegradable polymer matrix includes any two combinations of chitosan (CS), starch (ST), and polyvinyl alcohol (PVA); The biodegradable polymer matrix is ​​prepared into a matrix solution for use. Pyracantha fruit anthocyanins are functionally sensitive materials, and the biodegradable polymer matrix is ​​an organic framework material.

[0008] The intelligent food packaging film of the present invention uses firethorn fruit anthocyanin (G-ATH) to indicate changes in the volatile basic nitrogen (TVB-N) value, pH value, and ammonia index of meat products by color changes, thereby sensing and indicating changes in the freshness of meat products through color changes. The intelligent food packaging film of the present invention has superior ultraviolet blocking performance and can effectively block ultraviolet rays with wavelengths in the range of 200-500nm; among them, the chitosan / starch / anthocyanin food packaging film can block ultraviolet rays up to 500nm, allowing food to stay fresh for a longer period of time. The intelligent food packaging film of the present invention has the advantage of enhancing the antioxidant properties of food. Among them, the polyvinyl alcohol / starch / anthocyanin food packaging film has outstanding antioxidant properties and the best effect, which helps to keep food fresh for a long time.

[0009] Preferably, the mass ratio of firethorn fruit anthocyanins to the biodegradable polymer matrix is ​​1:5. The preferred method for preparing anthocyanins from thorny fruit is as follows: The dried firethorn berries were crushed into powder and passed through an 80-mesh sieve to ensure that the powder particle size did not exceed 180µm. The powder was mixed with a 60% (v / v) ethanol solution, and then the pH was adjusted to 2.0 ± 0.2 with 1M hydrochloric acid to obtain a slurry. The slurry was magnetically stirred at 25°C for 2-2.5 hours, then filtered through Whatman filter paper, and the filtrate was collected. The solvent was removed from the filtrate using a rotary evaporator to obtain a paste, which was then freeze-dried to obtain a powder, which was then stored at 4°C for later use.

[0010] Preferably, the mass-to-volume ratio (g / mL) of the powder to the ethanol solution is 1:20-25; and the pore size of the filter paper is 11µm.

[0011] Preferably, when the biodegradable polymer matrix is ​​starch and polyvinyl alcohol, the volume ratio of starch solution to polyvinyl alcohol solution in the matrix solution is 1:1; When the biodegradable polymer matrix is ​​starch and chitosan, the volume ratio of starch solution to chitosan solution in the matrix solution is 1:1; When the biodegradable polymer matrix is ​​polyvinyl alcohol and chitosan, the volume ratio of polyvinyl alcohol solution to chitosan solution in the matrix solution is 1:1.

[0012] Preferably, the starch solution is prepared by mixing starch with distilled water, and then stirring magnetically in a constant temperature water bath at 100°C for 1.5 hours until the starch is fully dissolved to obtain a starch solution. The polyvinyl alcohol solution is prepared by mixing polyvinyl alcohol with distilled water, and then stirring magnetically for 6 hours in a constant temperature water bath at 80°C until the polyvinyl alcohol is fully dissolved. The chitosan solution is prepared by mixing chitosan with a 1% (v / v) acetic acid solution and stirring magnetically at 50°C for 10 hours until the chitosan is fully dissolved, thus obtaining the chitosan solution.

[0013] Preferably, the mass-to-volume (g / mL) ratio of starch to distilled water is 1:45; The mass-to-volume ratio (g / mL) of polyvinyl alcohol to distilled water is 1:45; The mass-to-volume ratio (g / mL) of chitosan to acetic acid solution is 1:45.

[0014] Preferably, the plasticizer is glycerol, and the mass ratio of glycerol to the biodegradable polymer matrix is ​​3:10.

[0015] The above-mentioned intelligent food packaging film for monitoring meat freshness is prepared by the following method: A biodegradable polymer matrix solution and a plasticizer are mixed, and then firethorn fruit anthocyanins are added. After mixing, casting, and peeling, a smart food packaging film is obtained; the smart food packaging film has a freshness indication function.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The packaging film provided by the present invention is prepared from firethorn fruit anthocyanins (G-ATH) and biodegradable polymer matrix as raw materials. It has the advantages of being natural, safe and non-toxic, and environmentally friendly, and meets the requirements of green packaging.

[0017] 2. The packaging film of the present invention exhibits a distinct color gradient of firethorn fruit anthocyanins in the pH range of 2-12, from pink (fresh) to purple (less fresh) and then to blue-green (rotten). It has high contrast, is easy to identify with the naked eye, and has a sensitivity comparable to or even better than that of blueberry anthocyanins. It can accurately correspond to the concentration changes of volatile basic nitrogen (TVB-N) during the meat spoilage process. 3. The packaging film of the present invention, through the synergistic effect of the matrix and plasticizer, effectively encapsulates and protects the anthocyanin molecules of Pyracantha fortuneana fruit, slows down their degradation, extends the service life of the indicator film, and makes the packaging film have better stability.

[0018] 4. The packaging film of the present invention has a dense structure, good flexibility and tensile strength, giving it excellent mechanical properties; and the packaging film also has good barrier properties, and can be used as an inner packaging material or an independent label.

[0019] 5. The packaging film of this invention has a simple and environmentally friendly process, requires no complicated equipment, is easy to operate, and is environmentally friendly. Attached Figure Description

[0020] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the synthesis process of the intelligent food packaging film of the present invention.

[0022] Figure 2 Photographs showing the color changes of anthocyanins from Pyracantha fruit at different pH levels provided in Example 1. Figure 2 a) and the corresponding ultraviolet-visible spectrum ( Figure 2 b).

[0023] Figure 3 Images of the visibility of digital patterns under visible light for the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3.

[0024] Figure 4 The ultraviolet-visible spectra of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3 are shown.

[0025] Figure 5 The images show SEM images of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3; in the figures, a is the SEM image of Comparative Example 1, b is the SEM image of Comparative Example 2, c is the SEM image of Comparative Example 3; d is the SEM image of Example 2; e is the SEM image of Example 3; and f is the SEM image of Example 4.

[0026] Figure 6 The XRD patterns are of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3.

[0027] Figure 7 The FTIR spectra of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3 are shown.

[0028] Figure 8 The figures show the stress-strain curves of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3; in the figures, a is the stress-strain curve of Comparative Example 1 and Example 2, b is the stress-strain curve of Comparative Example 2 and Example 3, and c is the stress-strain curve of Comparative Example 3 and Example 4.

[0029] Figure 9 The figures show the water contact angle test results of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3; in the figures, a is the water contact angle result of Comparative Example 1, b is the water contact angle result of Example 2, c is the water contact angle result of Comparative Example 2, d is the water contact angle result of Example 3, e is the water contact angle result of Comparative Example 3, and f is the water contact angle result of Example 4.

[0030] Figure 10 The figures show the release rates of anthocyanins in the smart food packaging films provided in Examples 2-4; in the figures, a represents the release rate of Example 2, b represents the release rate of Example 3, and c represents the release rate of Example 4.

[0031] Figure 11 The figures show the thermal analysis curves of the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3; in the figures, a is the thermal analysis curve of Example 2 and Comparative Example 1, b is the thermal analysis curve of Example 3 and Comparative Example 2, and c is the thermal analysis curve of Example 4 and Comparative Example 3.

[0032] Figure 12 The results of the anti-oxidation test of DPPH on the smart food packaging films provided in Examples 2-4 and Comparative Examples 1-3 are shown.

[0033] Figure 13 Photographs showing the color change of the smart food packaging film provided in Examples 2-4 as pH fluctuates.

[0034] Figure 14 The results of the colorimetric reaction of the smart food packaging films provided in Examples 2-4 with ammonia are shown in the figures. In the figures, a is a photograph of the color change of each packaging film after being exposed to ammonia, and b is the sensitivity analysis result of each packaging film.

[0035] Figure 15 The results of tracking and detecting the freshness of chicken after packaging with the smart food packaging film provided in Example 2 are shown in the figure. In the figure, a is a photo of the color of chicken at different times, and b is the detection results of TVB-N content and pH of chicken stored at 25°C for 36 hours. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0037] Example 1 The preparation steps for pyracantha fruit anthocyanins are as follows: The dried firethorn berries were crushed into powder and passed through an 80-mesh sieve to ensure that the powder particle size did not exceed 180µm. The powder was mixed with a 60% (v / v) ethanol solution at a mass-to-volume (g / mL) ratio of 1:20. Then, the pH was adjusted to 2.0 with 1M hydrochloric acid to obtain the slurry; The slurry was magnetically stirred at 25°C for 2 hours, then filtered through Whatman filter paper with a pore size of 11 μm, and the filtrate was collected. The solvent was removed from the filtrate using a rotary evaporator to obtain a paste, which was then freeze-dried to obtain a powder, which was then stored at 4°C for later use.

[0038] Example 2 A smart food packaging film for monitoring meat freshness includes thorny fruit anthocyanins prepared in Example 1, a biodegradable polymer matrix, and a plasticizer; The biodegradable polymer matrix is ​​a combination of starch and polyvinyl alcohol; The plasticizer is glycerin; The preparation steps of the above-mentioned smart food packaging film are as follows: Step 1: Prepare starch solution and polyvinyl alcohol solution The starch solution is prepared by mixing starch with distilled water, with a mass-to-volume (g / mL) ratio of starch to distilled water of 1:45. Then, the starch was completely dissolved in a constant temperature water bath at 100℃ and magnetically stirred for 1.5 hours to obtain a starch solution. The polyvinyl alcohol solution is prepared by mixing polyvinyl alcohol with distilled water, wherein the mass-to-volume ratio (g / mL) of polyvinyl alcohol to distilled water is 1:45. Then, the polyvinyl alcohol was completely dissolved in a constant temperature water bath at 80℃ and magnetically stirred for 6 hours to obtain a polyvinyl alcohol solution. Step 2, Prepare the matrix solution Take starch solution and polyvinyl alcohol solution in a volume ratio of 1:1, mix them, and obtain matrix solution; Then glycerol was added to the matrix solution, with a mass ratio of glycerol to biodegradable polymer matrix of 3:10; Stir magnetically at 30°C for 15 minutes to mix thoroughly and obtain a mixed solution. Step 3: Prepare a precursor solution containing anthocyanins. Take the anthocyanin powder from Pyracantha fruit prepared in Example 1 and add it to the mixed solution; The mass ratio of firethorn fruit anthocyanin powder to biodegradable polymer matrix is ​​1:5. The anthocyanin powder from the firethorn fruit was magnetically stirred for 15 minutes at 30°C to uniformly disperse the powder in the mixed solution, thus obtaining a precursor solution containing anthocyanins. Step 4: Casting to form a film The precursor solution containing anthocyanins was slowly poured onto a glass disk measuring 250mm × 100mm to ensure that the precursor solution was evenly distributed on the surface of the glass disk. The glass dish was then placed in an incubator at 35°C for 20 hours to dry. During the drying process, the solvent in the solution gradually evaporated, forming a thin film. Step 5: Removing the packaging film and storing. After the film has dried, it is peeled off the glass plate to obtain the complete packaging film, namely ST / PVA / G-ATH packaging film. The peeled packaging film is stored in a dry, clean and light-proof environment for subsequent application in meat product packaging.

[0039] Comparative Example 1 The difference from Example 2 is that the anthocyanins from the firethorn fruit prepared in Example 1 are not added, and correspondingly, step three is not performed in the preparation of the smart food packaging film; the rest is the same as in Example 2, and the ST / PVA packaging film is obtained.

[0040] Example 3 A smart food packaging film for monitoring meat freshness includes thorny fruit anthocyanins prepared in Example 1, a biodegradable polymer matrix, and a plasticizer; The biodegradable polymer matrix is ​​a combination of starch and chitosan; The plasticizer is glycerin; The preparation steps of the above-mentioned smart food packaging film are as follows: Step 1: Prepare starch solution and chitosan solution The starch solution was prepared using the same process as in Example 2. The chitosan solution was prepared by mixing chitosan with a 1% (v / v) acetic acid solution, with a mass-to-volume (g / mL) ratio of chitosan to acetic acid solution of 1:45. Then, the mixture was magnetically stirred at 50°C for 10 hours to fully dissolve the chitosan and obtain a chitosan solution. Step 2, Prepare the matrix solution Starch solution and chitosan solution were taken in a volume ratio of 1:1 and mixed to obtain a matrix solution. Then glycerol was added to the matrix solution, with a glycerol to biodegradable polymer matrix mass ratio of 3:10; Stir magnetically at 30°C for 15 minutes to mix thoroughly and obtain a mixed solution. Step 3: Prepare a precursor solution containing anthocyanins. Take the anthocyanin powder from Pyracantha fruit prepared in Example 1 and add it to the mixed solution; The mass ratio of firethorn fruit anthocyanin powder to biodegradable polymer matrix is ​​1:5. The anthocyanin powder from the firethorn fruit was magnetically stirred for 15 minutes at 30°C to uniformly disperse the powder in the mixed solution, thus obtaining a precursor solution containing anthocyanins. Step 4: Casting to form a film The precursor solution containing anthocyanins was slowly poured onto a glass disk measuring 250mm × 100mm to ensure that the precursor solution was evenly distributed on the surface of the glass disk. The glass dish was then placed in an incubator at 35°C for 20 hours to dry. During the drying process, the solvent in the solution gradually evaporated, forming a thin film. Step 5: Removing the packaging film and storing. After the film has dried, it is peeled off the glass plate to obtain the complete packaging film, namely ST / CS / G-ATH packaging film. The peeled packaging film is stored in a dry, clean and light-proof environment for subsequent application in meat product packaging.

[0041] Comparative Example 2 The difference from Example 3 is that the anthocyanins from the firethorn fruit prepared in Example 1 are not added, and correspondingly, step three is not performed in the preparation of the smart food packaging film; otherwise, it is the same as Example 3, and the ST / CS packaging film is obtained.

[0042] Example 4 A smart food packaging film for monitoring meat freshness includes thorny fruit anthocyanins prepared in Example 1, a biodegradable polymer matrix, and a plasticizer; The biodegradable polymer matrix is ​​a combination of polyvinyl alcohol and chitosan; The plasticizer is glycerin; The preparation steps of the above-mentioned smart food packaging film are as follows: Step 1: Prepare polyvinyl alcohol solution and chitosan solution Polyvinyl alcohol solution, prepared in the same manner as in Example 2; Chitosan solution, prepared in the same manner as in Example 3; Step 2, Prepare the matrix solution Polyvinyl alcohol solution and chitosan solution were taken in a volume ratio of 1:1 and mixed to obtain a matrix solution. Then glycerol was added to the matrix solution, with a glycerol to biodegradable polymer matrix mass ratio of 3:10; Stir magnetically at 30°C for 15 minutes to mix thoroughly and obtain a mixed solution. Step 3: Prepare a precursor solution containing anthocyanins. Take the anthocyanin powder from Pyracantha fruit prepared in Example 1 and add it to the mixed solution; The mass ratio of firethorn fruit anthocyanin powder to biodegradable polymer matrix is ​​1:5. The anthocyanin powder from the firethorn fruit was magnetically stirred for 15 minutes at 30°C to uniformly disperse the powder in the mixed solution, thus obtaining a precursor solution containing anthocyanins. Step 4: Casting to form a film The precursor solution containing anthocyanins was slowly poured onto a glass disk measuring 250mm × 100mm to ensure that the precursor solution was evenly distributed on the surface of the glass disk. The glass dish was then placed in an incubator at 35°C for 20 hours to dry. During the drying process, the solvent in the solution gradually evaporated, forming a thin film. Step 5: Removing the packaging film and storing. After the film has dried, it is peeled off the glass plate to obtain the complete packaging film, namely PVA / CS / G-ATH packaging film. The peeled packaging film is stored in a dry, clean and light-proof environment for subsequent application in meat product packaging.

[0043] Comparative Example 3 The difference from Example 4 is that the anthocyanins prepared in Example 1 are not added, and therefore step three is not performed in the preparation of the smart food packaging film; otherwise, it is the same as Example 3, and a PVA / CS packaging film is obtained.

[0044] Detection: 1. Material Characterization 1.1 The surface features of the packaging films prepared in Examples 2-4 and Comparative Examples 1-3 were analyzed using scanning electron microscopy (SEM) at an accelerating voltage of 3 kV. The results are shown in the figure. Figure 5 ; Figure 5 In the figure, a is the SEM image of Comparative Example 1, b is the SEM image of Comparative Example 2, c is the SEM image of Comparative Example 3; d is the SEM image of Example 2; e is the SEM image of Example 3; and f is the SEM image of Example 4. 1.2 X-ray diffraction (XRD, using a Cu-Kα radiation source λ=1.540Å) was used to collect spectra of the packaging films prepared in Examples 2-4 and Comparative Examples 1-3 at 10–90° of 2θ. See [reference needed]. Figure 6 ; 1.3 FTIR spectrometer recordings were used at wavelengths of 500-4000 cm⁻¹. -1 Signals within the range were collected, and spectra of the packaging films prepared in Examples 2-4 and Comparative Examples 1-3 were obtained, see [reference needed]. Figure 7 ; 1.4 The optical properties of the synthesized film were analyzed using ultraviolet-visible spectroscopy, see [reference needed]. Figure 4 .

[0045] 2. Performance Testing 2.1 Observe and photograph the color changes of the Pyracantha fortuneana anthocyanin solution prepared in Example 1 at different pH values ​​under natural light, see... Figure 2 a; The UV-Vis absorption spectra of the solution in the wavelength range of 400-800 nm were recorded using a UV-Vis spectrophotometer. The results are shown in [Figure number missing]. Figure 2 b; The color changes of the smart food packaging films prepared in Examples 2-4 were observed and photographed under natural light at different pH values. Figure 13 ; 2.2 The smart food packaging films prepared in Examples 2-4 were made into film samples of 1.0cm × 1.0cm. The film samples were then immersed in 15mL of 5.0M ammonia water and placed at 25°C for 24 minutes. The colors of the film samples at 0h and 24h were recorded. (See attached figures). Figure 14 a) and analyzed using Adobe Photoshop 2007 software; the results are shown below. Figure 14 b; 2.3 The smart food packaging film prepared in Example 2 was made into a 1.0cm × 1.0cm film. The film was then placed in a 20cm × 15cm sealed polyethylene bag containing 100g of unspoiled chicken. The film was stored at 25°C for 0, 12, 24, and 36 hours. The color change of the film was observed and photographed. (See attached image). Figure 15 a; During storage, 10g of chicken was homogenized in 100mL of distilled water, and 1.0g of magnesium oxide was added. The total volatile basic nitrogen (TVB-N) content was determined using the Kjeldahl method. The distillate was placed in a flask containing 10mL of 2% boric acid solution and reacted with 0.01M HCl solution. A blank solution was used as a control. The results are shown in [Figure number missing]. Figure 15 b; 3. Test Results Figure 2 middle, Figure 2 a shows the color changes of the anthocyanins prepared in Example 1 under conditions of pH 2–12; combined with Figure 2 As can be seen, anthocyanins exhibit distinct color changes with pH: under strongly acidic conditions (pH 2-3), the solution is orange-red; under slightly acidic conditions (pH 4-6), the color turns yellow; under neutral to slightly alkaline conditions (pH 7-8), it is yellow-green; and under relatively alkaline conditions (pH 9-12), the solution turns brown. These color changes are caused by alterations in the molecular structure of anthocyanins due to pH variations. Figure 2 b shows the visible light absorption capacity of the anthocyanins prepared in Example 1 under pH conditions of 2-12. Overall, the absorbance shows a decreasing trend with increasing wavelength. Significant differences in the curves at different pH values ​​are observed in the short-wavelength region (400-500 nm), indicating that pH has a significant impact on absorption in this region. In the long-wavelength region (700-800 nm), all pH curves almost overlap, indicating that pH has little effect on long-wavelength absorption. The visible light absorption characteristics of the anthocyanins prepared in Example 1 are affected by pH, with the main influence concentrated in the short-wavelength region; absorption in the long-wavelength region is largely unaffected by acidic or alkaline environments.

[0046] When food is exposed to light, it oxidizes faster and produces harmful byproducts, thus accelerating food spoilage. Therefore, the ability to block ultraviolet and visible light is a key performance indicator for food packaging. Figure 3 Visual images of the packaging films of Examples 2-4 and Comparative Examples 1-3 are shown; Figure 4 The light transmission properties of the packaging films of Examples 2-4 and Comparative Examples 1-3 are shown. Combination Figure 3 It can be seen that the packaging film without anthocyanins (blank group) is colorless and highly transparent, while the packaging film with anthocyanins is pink to dark yellow. Figure 4 The ultraviolet-visible light transmission spectra of each packaging film are given, combined with... Figure 4 It is evident that the packaging film (containing anthocyanins) provided by the present invention has lower visible light transmittance (higher opacity) than the packaging film (without anthocyanins) provided in the comparative example, and can effectively block ultraviolet light with wavelengths ≤450nm and some visible light; among them, the packaging film (ST / CS / G-ATH packaging film) provided in Example 3 can extend the blocking range to 500nm; due to the strong light absorption properties of anthocyanins, the film with added anthocyanins has a significant blocking effect on ultraviolet light and some visible light; thus, it is shown that the interaction between anthocyanins and the biodegradable polymer matrix significantly regulates the light transmittance and visual appearance of the film; Figure 5 In China, combined Figure 5 As can be seen, the packaging film provided in Comparative Example 1 shows a smooth texture with no visible particles, exhibiting a biphase structure, which can be attributed to the partial immiscibility between the two polymers and their different densities. Combination Figure 5 b. It can be seen that the packaging film provided by Comparative Example 2 exhibits a smooth surface, indicating enhanced compatibility between chitosan and starch, with no obvious phase separation. Combination Figure 5 c. It can be seen that the packaging film provided by Comparative Example 3 exhibits a smooth morphology and the smallest grains, indicating that there is good compatibility between chitosan and polyvinyl alcohol, with no signs of microphase separation. However, the packaging films with added anthocyanins (ST / PVA / G-ATH in Example 2, ST / CS / G-ATH in Example 3, and CS / PVA / G-ATH in Example 4) exhibited heterogeneous particles with uneven surfaces, see... Figure 5 d, 5e, and 5f indicate that anthocyanins have been successfully incorporated into the biodegradable polymer matrix. Combination Figure 6It can be seen that the diffraction peak at 19.8° (corresponding to the (101) crystal plane) of the packaging films prepared in Comparative Example 1 and Comparative Example 3 is attributed to the characteristic diffraction of polyvinyl alcohol (PVA); the packaging film prepared in Comparative Example 1 shows a characteristic peak related to starch molecules at 16.8° (corresponding to the (111) crystal plane), while the packaging film prepared in Comparative Example 3 shows a characteristic peak related to chitosan at 19.8° (corresponding to the (101) crystal plane). In addition, the packaging film prepared in Comparative Example 2 shows peaks at 11.6° (corresponding to the (020) crystal plane) and 20.3° (corresponding to the (110) crystal plane), respectively, which are attributed to the characteristic diffraction of chitosan. The peak intensity weakens and shifts with the addition of anthocyanins, which may be attributed to the hydrogen bond interaction between the polymer and anthocyanins, which changes the order of the crystal.

[0047] The bonding between the biodegradable polymer matrix and anthocyanins was studied using infrared spectroscopy analysis; all films were analyzed at 3000 to 3500 cm⁻¹. -1 Both have relatively broad infrared absorption peaks, see Figure 7 , corresponding to the stretching vibration of hydroxyl (–OH) or amino (N–H); 2942 cm -1 and 2834cm -1 The peaks at [values] represent the C–H stretching vibrations of methylene (–CH2–) and methyl (–CH3), respectively; furthermore, the packaging film prepared in Example 2 [values] at 1082 cm⁻¹ -1 (Stretching vibration of CO in the CO group) and at 1024 cm⁻¹ -1 A stronger peak than that of the packaging film in Comparative Example 1 was observed at the stretching and bending vibrations of the COC group; the packaging film containing anthocyanins (the packaging films prepared in Examples 2-4) showed a peak at 1630 cm⁻¹. -1 The appearance of peaks nearby is attributed to the stretching vibration of C=C in the aromatic ring; the intensity of these peaks increases with the addition of anthocyanins; anthocyanins are a class of multifunctional compounds rich in -OH, C=O functional groups and aromatic rings, and have infrared activity; they interact with the polymer matrix through hydrogen bonds and other molecular interactions, and change the vibrational energy of the bonds, resulting in an increase in peak intensity; The mechanical properties of packaging films are crucial for ensuring their suitability for food packaging applications, as they affect durability, flexibility, and resistance to external forces; optimal strength ensures protection against damage, contamination, and environmental factors, maintaining quality and shelf life. The mechanical properties of the packaging films prepared in Examples 2-4 and Comparative Examples 1-3 were tested, and the stress-strain curves are shown below. Figure 8 As shown; combined Figure 8It can be seen that the packaging film prepared in Example 4 has the highest TS (32.26±3.53MPa), the packaging film prepared in Example 2 has the highest EB (37.89±2.25%), and the packaging film prepared in Example 3 has a TS value of 10.76±2.27MPa and an EB value of 2.34±0.56%, indicating poor brittleness. This decrease in stretchability can be attributed to the disruption of intermolecular and intramolecular hydrogen bonds in the biodegradable polymer matrix caused by the addition of anthocyanins. Mechanical properties depend on factors such as film composition, anthocyanin source, mixing ratio, plasticizer, and storage conditions. Combined with the test results, it can be seen that the packaging films prepared in Comparative Example 1 and Example 2 exhibit superior mechanical properties on average compared to Examples 3 and 4, possibly due to the stronger interaction between the phenolic-OH groups of polyvinyl alcohol, starch, and anthocyanins. Figure 9 In the table, 'a' represents the water contact angle result of Comparative Example 1, 'c' represents the water contact angle result of Comparative Example 2, and 'e' represents the water contact angle result of Comparative Example 3; combined with... Figure 9 It can be seen that the WCA of the packaging film prepared in Comparative Example 1 is 44.88°, the WCA of the packaging film prepared in Comparative Example 2 is 49.80°, and the WCA of the packaging film prepared in Comparative Example 3 is 53.78°, indicating that the WCA of the chitosan-based composite material is relatively high. The packaging film prepared in Example 2 had a water contact angle (WCA) of 59.98°, the packaging film prepared in Example 3 had a WCA of 53.17°, and the packaging film prepared in Example 4 had a WCA of 60.79°, indicating that the chitosan-based composite material had a high WCA. This indicates that the addition of anthocyanins further improved the water contact angle (WCA) of the packaging film. The increased water contact angle can be attributed to the interaction between anthocyanins and the polar functional groups of the polymer, which limits the availability of these groups to interact with water on the film surface. Anthocyanin release tests were conducted on the packaging films provided in Examples 2-4 to evaluate their compatibility with different food imitators, namely distilled water and ethanol, representing water-containing and fat / alcohol-containing food systems, respectively. The results are shown in [Figure Number]. Figure 10 ; Figure 10The results show the anthocyanin release rates in the packaging films prepared in Examples 2-4. The results indicate that, among the tested simulants (distilled water, 40% ethanol solution, and 50% ethanol solution), the highest anthocyanin release occurred in distilled water, followed by 40% ethanol, and then 50% ethanol. The higher release in distilled water is mainly due to the higher polarity of water, which enhances the solubility of anthocyanins. The release behavior is influenced not only by the polarity of the simulants but also by the swelling capacity and solubility of the packaging film. The anthocyanin release rates in the packaging films prepared in Examples 3 and 4 are lower than those in the packaging film prepared in Example 2. This is because the interactions between chitosan and water molecules, especially the stronger hydrogen bonding, hinder the diffusion of anthocyanin molecules into the release medium. Thermogravimetric analysis (TGA) was performed on the packaging films prepared in Examples 2-4 and Comparative Examples 1-3. The results are shown in the figure. Figure 11 ; combination Figure 11 Thermogravimetric analysis (TGA) of all packaging films showed four distinct weight loss phases: the first phase, occurring between 20-120°C, was due to the vaporization of moisture and other volatile solvents present on the packaging film surface; the second phase, observed between 120-200°C, corresponded to the release of bound water and the volatilization of glycerol; the third phase, occurring between 200-450°C, was primarily due to the decomposition of the biodegradable polymer matrix and anthocyanins in the packaging film; and the fourth phase, a small weight loss was observed between 450-800°C, due to further thermal decomposition of the remaining packaging film residue. At 800°C, the net weight loss rates of the packaging films prepared in Comparative Examples 1, 2, and 3 were 92.79%, 73.70%, and 88.66%, respectively; while the net weight loss rates of the packaging films prepared in Examples 2, 3, and 4 were 87.07%, 67.65%, and 82.37%, respectively. These results indicate that the addition of anthocyanins significantly enhances the stability of the packaging films. The antioxidant properties of the packaging films prepared in Examples 2-4 and Comparative Examples 1-3 were analyzed by DPPH free radical scavenging experiments. The results are shown in the figure. Figure 12 ; combination Figure 12It can be seen that the antioxidant activity of the anthocyanin-containing packaging film is ranked in the order of Comparative Example 3 > Comparative Example 2 > Comparative Example 1. The superior activity of the chitosan-containing packaging film is attributed to the amino groups of chitosan, which can effectively neutralize free radicals, while starch and polyvinyl alcohol lack this functional group. Combining the results of Examples 2-4, it can be seen that the packaging film has a higher scavenging ability after the addition of anthocyanins, which is attributed to the presence of phenol groups in anthocyanins, enabling them to scavenge free radicals through phenols and neutralize free radicals by forming phenoxy groups. It is worth noting that the packaging film prepared in Example 2 has slightly higher antioxidant activity than the packaging films prepared in Examples 3 and 4. This is because chitosan creates an alkaline environment during film formation to reduce antioxidant activity, thereby reducing the total phenol content. The above results indicate the potential application of anthocyanin-containing packaging films as active packaging film materials with antioxidant activity. Figure 13 The color response of the packaging films prepared in Examples 2-4 at different pH values ​​is shown. The packaging film prepared in Example 2 exhibits the best performance, displaying red at pH 2-5, light brown at pH 6-8, and light green to dark green above pH 9. These color changes correspond to modifications of the anthocyanin molecular structure: yellow ions at low pH, methanol pseudobase at moderately alkaline conditions, and chalcone forms at even more alkaline conditions. Comparison with Comparative Examples 1-3 further confirms that the pH response of the packaging film is caused by anthocyanins. Figure 2 The anthocyanin response in a is consistent with that in a; Figure 14 Digital images and sensitivity responses of the packaging films prepared in Examples 2-4 to ammonia exposure are presented. Ammonia diffuses into the packaging film, creating an alkaline environment and increasing the pH. Due to the pH sensitivity of anthocyanins, the films with added anthocyanins undergo color changes, followed by structural rearrangement. Among them, the packaging film prepared in Example 2 has the highest sensitivity to ammonia (77.88%), followed by the packaging film prepared in Example 4 (52.29%), and the packaging film prepared in Example 3 has the lowest sensitivity (10.68%). Combination Figure 13 It can be seen that the packaging film prepared in Example 2 has the highest sensitivity to color changes. Therefore, the packaging film prepared in Example 2 was used to track the freshness of chicken, and the results are shown in [Figure 2]. Figure 15 ; combination Figure 15 It can be seen that at 25℃, the packaging film shows obvious color changes corresponding to the freshness of the meat: it is red before 12 hours, indicating that the meat is fresh; it turns dark green after 24 hours, indicating that the chicken has begun to spoil; and by 36 hours, the packaging film gradually turns brown, effectively indicating the degree of spoilage of the meat. TVB-N is a widely used parameter for monitoring meat spoilage; an increase in its content reflects greater microbial degradation. In protein-rich products such as meat, spoilage mainly leads to the production of alkaline nitrogen compounds, including ammonia and amines, resulting in an increase in pH. According to relevant standards, chicken is considered fresh when its TVB-N content is below 15 mg / 100g, slightly fresh when it is between 15-30 mg / 100g, and spoiled when it exceeds 30 mg / 100g. Figure 15 The results showed that the TVB-N level steadily increased over time, with an initial value of 6.35±0.68 mg / 100g, increasing to 14.32±0.71 mg / 100g within 12 hours, 28.84±0.49 mg / 100g after 24 hours, and 36.74±0.6 after 36 hours. The pH gradually increased over time, with the initial pH of the chicken meat being 6.03±0.07, gradually increasing to 6.51±0.03, 7.6±0.08, and 8.42±0.06 at 12 hours, 24 hours, and 36 hours, respectively. Combined with the TVB-N and pH results after 24 hours, this indicates that the chicken meat was not fresh and had begun to spoil.

[0048] The packaging film prepared by this invention can sensitively indicate the volatile basic nitrogen (TVB-N) value, pH, ammonia and other indicators of meat products by color changes, so that the freshness of meat products can be sensed and judged simply and quickly based on the color change of the packaging film. The packaging film prepared by this invention has ultraviolet blocking properties, effectively blocking ultraviolet rays with wavelengths in the range of 200-500nm, and also has the function of enhancing the antioxidant properties of food. In practical applications, the intelligent food packaging film prepared by this invention is used for meat packaging, such as chicken packaging. After packaging, the color change of the film is observed, and a comprehensive judgment is made in combination with the TVB-N value and pH value of the meat. For example, under 25°C conditions, if the film color changes from pink to brown after 36 hours of packaging chicken, and the TVB-N value of the chicken reaches about 36.74 mg / 100g and the pH value is about 8.42, it indicates that the chicken has spoiled. In this way, the freshness of meat can be effectively monitored, providing reliable quality assurance for the storage, transportation, and sales of meat products. This provides a practical approach for the packaging industry to ensure food quality, improve food safety monitoring levels, and promote the development of environmentally friendly intelligent food packaging.

[0049] Although the present invention has been described in detail with reference to preferred embodiments, it is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the claims.

Claims

1. A smart food packaging film for monitoring the freshness of meat, characterized in that: Including thorny fruit anthocyanins, biodegradable polymer matrix, and plasticizers; The biodegradable polymer matrix includes any two combinations of chitosan (CS), starch (ST), and polyvinyl alcohol (PVA); The biodegradable polymer matrix is ​​prepared into a matrix solution for use.

2. The intelligent food packaging film for monitoring meat freshness as described in claim 1, characterized in that, The mass ratio of firethorn fruit anthocyanins to the biodegradable polymer matrix is ​​1:

5.

3. The intelligent food packaging film for monitoring meat freshness as described in claim 1, characterized in that, The preparation method of anthocyanins from firethorn fruit is as follows: The dried firethorn berries were crushed into powder and passed through an 80-mesh sieve to ensure that the powder particle size did not exceed 180µm. The powder was mixed with a 60% (v / v) ethanol solution, and then the pH was adjusted to 2.0 ± 0.2 with 1M hydrochloric acid to obtain a slurry. The slurry was magnetically stirred at 25°C for 2-2.5 hours, then filtered through Whatman filter paper, and the filtrate was collected. The solvent was removed from the filtrate using a rotary evaporator to obtain a paste, which was then freeze-dried to obtain a powder, which was then stored at 4°C for later use.

4. The intelligent food packaging film for monitoring meat freshness as described in claim 3, characterized in that, The mass-to-volume ratio (g / mL) of the powder to the ethanol solution is 1:20-25; the pore size of the filter paper is 11µm.

5. The intelligent food packaging film for monitoring meat freshness as described in claim 1, characterized in that, When the biodegradable polymer matrix is ​​starch and polyvinyl alcohol, the volume ratio of starch solution to polyvinyl alcohol solution in the matrix solution is 1:

1. When the biodegradable polymer matrix is ​​starch and chitosan, the volume ratio of starch solution to chitosan solution in the matrix solution is 1:1; When the biodegradable polymer matrix is ​​polyvinyl alcohol and chitosan, the volume ratio of polyvinyl alcohol solution to chitosan solution in the matrix solution is 1:

1.

6. The intelligent food packaging film for monitoring meat freshness as described in claim 5, characterized in that, The starch solution is prepared by mixing starch with distilled water, and then stirring magnetically in a constant temperature water bath at 100°C for 1.5 hours until the starch is fully dissolved. The polyvinyl alcohol solution is prepared by mixing polyvinyl alcohol with distilled water, and then stirring magnetically for 6 hours in a constant temperature water bath at 80°C until the polyvinyl alcohol is fully dissolved. The chitosan solution is prepared by mixing chitosan with a 1% (v / v) acetic acid solution and stirring magnetically at 50°C for 10 hours until the chitosan is fully dissolved, thus obtaining the chitosan solution.

7. The intelligent food packaging film for monitoring meat freshness as described in claim 6, characterized in that, The mass-to-volume ratio (g / mL) of starch to distilled water is 1:45; The mass-to-volume ratio (g / mL) of polyvinyl alcohol to distilled water is 1:45; The mass-to-volume ratio (g / mL) of chitosan to acetic acid solution is 1:

45.

8. The intelligent food packaging film for monitoring meat freshness as described in claim 1, characterized in that, The plasticizer is glycerol, and the mass ratio of glycerol to the biodegradable polymer matrix is ​​3:

10.

9. A method for preparing a smart food packaging film for monitoring meat freshness as described in claim 1, characterized in that, The process is as follows: A biodegradable polymer matrix solution and a plasticizer are mixed, and then firethorn fruit anthocyanins are added. After mixing, casting, and peeling, a smart food packaging film is obtained; the smart food packaging film has a freshness indication function.

Images