Plant polyphenol-complex selenium nano-state active intelligent fresh-keeping film and preparation method and application thereof

Abstract

The application discloses a kind of plant polyphenol-composite selenium nano-state active intelligent preservative film and its preparation method and application, belong to food active packaging and intelligent packaging material technical field.The application is formed by polyphenol and selenium component composite nanoparticle, and is added to the preparation active film layer of base film forming liquid;While introducing the natural extract rich in anthocyanin into film forming liquid to construct local pH indicating area, and obtain double-layer active intelligent preservative film by stratified film forming.The selenium includes selenium amino acid, selenium peptide, organic selenium such as selenoprotein and inorganic selenium.The obtained preservative film has antioxidant, bacteriostatic preservation and freshness visual monitoring function, and can reflect the quality change of food, especially meat product during storage by color change.The preservative film preparation process is simple, safe and environmentally friendly, and has good application prospect in food preservation packaging field.

Description

Technical Field

[0001] This invention relates to a plant polyphenol-composite selenium nano-state active smart preservation film, its preparation method and application, belonging to the technical field of food active packaging and smart packaging materials. Background Technology

[0002] Fresh meat, fish, and other high-moisture foods are susceptible to microbial contamination, lipid oxidation, protein decomposition, and enzymatic reactions during storage, transportation, and sales. This can lead to problems such as off-flavors, discoloration, juice loss, textural deterioration, and decreased nutritional quality. Meat, in particular, is rich in protein, fat, and water; even under refrigeration, microbial proliferation and spoilage can occur, producing volatile basic nitrogen and amines, thus reducing its edibility and safety. Therefore, developing packaging materials that can delay food spoilage, maintain food quality, and reflect changes in food freshness is of great significance.

[0003] Currently, food packaging still primarily uses traditional petroleum-based plastics. While these materials offer advantages such as low cost, ease of processing, and good mechanical properties, their main function is typically limited to physical barriers and external protection, with limited active inhibition of microbial growth and oxidative deterioration during food storage. Furthermore, traditional plastics are difficult to degrade, easily causing environmental pollution and contradicting the trend towards green and sustainable packaging. In addition, ordinary packaging materials generally cannot visually reflect changes in food freshness; consumers often rely on production dates, expiration dates, or sensory evaluations, which introduces a degree of lag and subjectivity.

[0004] Active packaging introduces antibacterial and antioxidant functional components into packaging materials, enabling packaging films to not only act as barriers but also actively delay food quality deterioration. Nano-selenium, a functional selenium material with nanoscale characteristics, possesses certain antioxidant and antibacterial potential and can be used to enhance the active preservation performance of packaging films. Due to its small particle size and large specific surface area, nano-selenium exhibits high surface activity, attracting attention in functional material development. However, nano-selenium particles are prone to agglomeration during preparation and application, leading to increased particle size, decreased dispersibility and stability, and affecting its uniform distribution and functionality in the membrane matrix. Therefore, appropriate stabilization methods are needed to improve the dispersion stability and application effect of nano-selenium. The phenolic hydroxyl groups and other active groups in polyphenol molecules can form hydrogen bonds and electrostatic interactions with the surface of nano-selenium particles or natural polymer segments, which can help regulate the formation and dispersion state of nano-selenium to some extent. Combining polyphenols with nano-selenium can not only improve the agglomeration problem of nano-selenium but also potentially enhance the stability and functional retention of active components in membrane materials. Therefore, introducing the polyphenol-nano selenium composite system into natural polymer packaging films is an effective approach to improve the antioxidant, antibacterial, and preservation properties of packaging films.

[0005] Smart packaging can visually reflect changes in food quality through color variations. Among these, pH-responsive color-indicating smart films show promise for monitoring the freshness of meat and seafood due to their ease of use and intuitive observation. Volatile amines produced during food spoilage cause pH changes in the packaging microenvironment; pH-sensitive dyes can change color with variations in acidity and alkalinity, thus indicating food freshness. Natural anthocyanins are common pH-responsive indicators and can be used to prepare freshness-indicating films.

[0006] However, existing active packaging films and smart indicator films are mostly used as relatively independent systems. While single active preservation films can delay food spoilage to some extent, they are difficult to visually display food freshness; single smart indicator films, while reflecting changes in food condition, typically lack active preservation capabilities. Some composite films, although incorporating both active and indicator components, may still suffer from problems such as uneven dispersion of functional components, unclear indicator areas, insufficient membrane structural stability, and unintuitive color responses. Therefore, it is necessary to develop an active smart packaging film material with a reasonable structure, simple preparation, and both active preservation and visual freshness monitoring functions to meet the application requirements of green preservation packaging for fresh food. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a plant polyphenol-composite selenium nanoparticle active smart preservation film, its preparation method, and its application. The method involves forming composite nanoparticles of polyphenols and selenium components and adding them to a base film-forming solution to prepare an active film layer. Simultaneously, a natural extract rich in anthocyanins is introduced into the film-forming solution to construct a local pH indicator zone. Through layered film formation, a double-layer active smart preservation film is obtained. When used for packaging fresh beef, the polyphenol-nano selenium film slows down microbial proliferation, protein decomposition, and lipid oxidation. Color changes in the local pH indicator zone reflect the freshness of the beef, and the outer base protective film layer enhances the film's integrity and stability.

[0008] This invention is achieved through the following technical solution: The first objective of this invention is to provide a method for preparing a plant polyphenol-composite selenium nano-state active smart food preservation film, comprising the following steps: S1. Polyphenol-selenium composite nanoparticles are formed by combining polyphenols and selenium compounds. S2. Add polyphenol-selenium composite nanoparticles to the basic film-forming solution at 1%~3% of the dry matter mass of the basic film-forming solution and mix evenly to obtain the inner active film-forming solution. S3. Add the anthocyanin solution or anthocyanin-rich extract to the base film-forming solution and mix well to obtain a pH-indicating film-forming solution. S4. The inner layer active film-forming liquid is poured into the film-forming carrier and left to stand until the inner layer active film-forming liquid forms a gel. The film-forming carrier has a mold for forming a reserved indicator area, and the area of ​​the mold accounts for 2% to 5% of the area of ​​the film-forming carrier. S5. Remove the mold, add pH indicator film-forming solution to the reserved indicator area, let stand until the pH indicator film-forming solution forms a gel, and dry to form a film to obtain an inner active indicator film with a local pH indicator area. S6. A basic film-forming solution is uniformly coated on the surface of the inner active indicator membrane, and then dried again to form a film, thus obtaining a double-layer active smart membrane with a local pH indicator area.

[0009] In one embodiment of the present invention, the selenium compound is one or more of inorganic selenium, selenoamino acids, selenopeptides, and selenoproteins.

[0010] In one embodiment of the present invention, the polyphenol-selenium composite nanoparticles can be prepared by the following method: S01. Stir the aqueous solution of 40-60 mM selenium compound at 50-60 °C to adjust the pH of the system to 4.0-4.5; S02. Add ascorbic acid aqueous solution dropwise to the aqueous solution of selenium compound in S01, then add polyphenol solution, stir and react for 40-60 min, cool and let stand, centrifuge to remove supernatant, wash and dry to obtain polyphenol-selenium composite nanoparticles; wherein, the molar ratio of selenium compound to ascorbic acid is 1:7-9, and the molar ratio of selenium compound to polyphenol is 1:4.5-5.5.

[0011] In one embodiment of the present invention, the base film-forming solution is composed of gelatin, κ-carrageenan, glycerol and water; wherein the concentration of the gelatin solution is 1% to 2.5%, the concentration of the κ-carrageenan solution is 0.2% to 0.5%, and the amount of glycerol added is 25% to 40% of the total dry weight of the film-forming solution.

[0012] In one embodiment of the present invention, the polyphenol is one or more of dihydromyricetin, silymarin, quercetin, resveratrol, curcumin, and puerarin.

[0013] In one embodiment of the present invention, in step S4, the standing time is 2-40 minutes. In the present invention, the standing time allows the inner layer active film-forming liquid to form a gel-like or semi-gel-like structure before the local indicator area molding mold is removed, so that the subsequent addition of anthocyanin-containing film-forming liquid will not cause dispersion.

[0014] In one embodiment of the present invention, the anthocyanin is added at 0.75% to 1.5% of the dry matter mass of the base film-forming solution, and the anthocyanin is derived from one or more of blueberries, purple sweet potatoes, purple cabbage, black goji berries, mulberries, black rice, or grape skins.

[0015] In one embodiment of the present invention, in step S6, a base film-forming solution is uniformly coated onto the surface of the inner active indicator membrane as an outer base protective membrane layer, and the volume ratio of the inner active film-forming solution to the film-forming solution of the outer base protective membrane layer is 1.5~2.5:1. In the present invention, the outer base protective membrane layer does not contain polyphenols / nano selenium and anthocyanins; the outer base protective membrane layer is used to cover and protect the inner active indicator membrane and improve the mechanical properties of the membrane.

[0016] In one embodiment of the present invention, the drying film is formed by drying at 35~45°C for 3~5 hours.

[0017] A second objective of this invention is to provide a bilayer active smart membrane prepared by the method described above.

[0018] A third objective of this invention is to provide the application of the aforementioned double-layer active smart film in food preservation.

[0019] In one embodiment of the present invention, the food is fresh meat, fish, or other high-moisture foods.

[0020] The beneficial effects of this invention are: 1. The present invention adopts a double-layer structure design, which combines the active preservation area of ​​polyphenol-composite selenium nanostate, the local pH indicator area and the outer basic protective film layer, so that the film has preservation, indicator and structural protection functions at the same time.

[0021] 2. The present invention forms a local pH indicator zone, the area of ​​which is 2% to 5% of the total membrane area. This confines anthocyanins within the local pH indicator zone, avoiding the problems of anthocyanins being evenly distributed throughout the membrane, resulting in an overly dark membrane color, inconvenient observation, increased dosage, or impaired membrane performance. This not only enables visual freshness indication but also does not affect the preservation effect of polyphenol-composite selenium nanoparticles in the main membrane area.

[0022] 3. This invention improves the overall performance of the active smart membrane and its preservation effect on fresh beef by adjusting the amount of polyphenol-selenium composite nanoparticles added.

[0023] 4. When the double-layer active smart film obtained by the present invention is used for packaging fresh beef, it can delay the increase of pH, the increase of total bacterial count, the generation of volatile basic nitrogen and the accumulation of malondialdehyde, and can reflect the freshness of fresh beef through the color change of the local pH indicator area. Attached Figure Description

[0024] 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 of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Characterization of polyphenol-nano selenium, including (A) UV-Vis spectroscopy; (B) FTIR spectroscopy; (C) XRD diffraction; (D) particle size; (EF) SEM; Figure 2 To optimize the synthesis conditions of nanoparticles, the following factors were considered: (A) selenoic acid ratio; (B) selenopolyphenol ratio; (C) pH; (D) temperature; and (E) reaction time. Figure 3 The antibacterial activity of polyphenol-nano selenium is determined by (A) plate count and (B) antibacterial rate. Figure 4 This is a schematic diagram illustrating the preparation process and structure of a bilayer membrane. Figure 5 For the characterization of the bilayer film, (A) UV-Vis spectrum; (B) FTIR spectrum; (C) XRD diffraction; (D) opacity; (E) moisture content; (F) water contact angle; (G) water vapor transmission rate; (H) oxygen transmission rate; (I) mechanical properties; Figure 6 The following are the physicochemical properties of beef during cold storage, including (A) pH; (B) total bacterial count; (C) volatile basic nitrogen; and (D) malondialdehyde content. Figure 7 The image shows the color change and color difference results of the local pH indicator area, where (A) color photo matrix; (B) correlation between color and spoilage index; (C) ΔE; (D) L* value; (E) a* value; and (F) b* value. Detailed Implementation

[0026] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] Source of raw materials Polyphenol raw materials: dihydromyricetin, silymarin, quercetin, resveratrol, curcumin and puerarin, etc.; in the specific embodiment, dihydromyricetin (DMY, CAS No. 27200-12-0) is used.

[0028] Sodium selenite (Na2SeO3): CAS No. 10102-18-8.

[0029] Ascorbic acid (Vc): CAS No. 50-81-7.

[0030] Gelatin: Purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] κ-carrageenan: CAS No. 11114-20-8.

[0032] Anthocyanin raw materials: Anthocyanin solution or natural extracts rich in anthocyanins can be used. The natural extracts can be derived from blueberries, purple sweet potatoes, purple cabbage, black goji berries, mulberries, black rice or grape skins, etc. In the specific embodiment, blueberry-derived anthocyanins (5%~25%) were used and purchased from Shanghai Yuanye Technology Co., Ltd.

[0033] Detection method: 1. Characterization methods for polyphenol-nano selenium The obtained polyphenol-nano selenium was characterized in structure and morphology. UV-Vis absorption spectroscopy was used to determine its absorption characteristics to analyze the spectral differences between polyphenols, nano selenium, and polyphenol-nano selenium; Fourier transform infrared spectroscopy was used to analyze its functional group changes to determine the interaction between polyphenols and nano selenium; X-ray diffraction was used to analyze its crystal structure changes; and scanning electron microscopy was used to observe its morphological characteristics.

[0034] The above characterization results are used to explain the formation of polyphenol-nano selenium and its structural basis as an active preservative.

[0035] 2. Antibacterial activity of polyphenol-nano selenium To determine the antibacterial activity, refer to GB / T 21510-2024, "Test Method for Antibacterial Properties of Nano-Inorganic Materials," and adjust the bacterial concentration cultivated to the logarithmic growth phase to 1×10⁻⁶. 8 CFU / mL, the bacterial culture was mixed with an equal volume of the sample, and the positive control was ampicillin sodium. After incubation at 37 ℃ in a shaker for 24 h, the culture was serially diluted with sterile physiological saline, and 100 μL of the diluted solution was evenly spread on LB agar plates. After incubation at 37 ℃ upside down for 24 h, the agar plates were counted.

[0036] Antibacterial activity was determined using 96-well plates, and the inhibition rate was calculated by reflecting bacterial concentration using OD600. The bacterial concentration was adjusted to 1×10⁻⁶ cells after culture to the logarithmic growth phase. 8 CFU / mL, the bacterial culture was mixed with the sample in equal volume, and the positive control was ampicillin sodium. After mixing, OD600 was measured and the mixture was incubated in a shaker at 37 ℃ for 24 h. OD600 was measured again.

[0037] 3. Method for recording the appearance of beef Fresh beef under different packaging treatments was sampled periodically during refrigeration and photographed to form a matrix of beef appearance photos during refrigeration, which was used to record changes in sample color and surface condition.

[0038] 4. pH Measurement Method Refer to GB5009.237-2016 Determination of pH in food.

[0039] 5. Method for determining total bacterial count Refer to GB4789.2-2022 for the determination of total bacterial count.

[0040] 6. Method for determining volatile basic nitrogen content Refer to GB5009.228-2016 Determination of volatile basic nitrogen in food.

[0041] 7. Method for determining malondialdehyde content Refer to GB5009.181-2016 Determination of malondialdehyde in food.

[0042] 8. pH indicator area color measurement method During the cold storage of beef, the color changes of local pH indicator areas in the double-layer active smart membrane were observed and photographed regularly to form a color change photograph matrix. At the same time, the L*, a*, and b* values ​​of the local pH indicator areas were measured using a colorimeter, and the total color difference ΔE was calculated.

[0043] The total color difference ΔE is calculated using the following formula:

[0044] Wherein, ΔL*, Δa*, and Δb* represent the changes in L*, a*, and b* values ​​relative to the initial state at different storage time points, respectively.

[0045] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0046] Example 1: Synthesis of dihydromyricetin-nano selenium (1) Synthesis of dihydromyricetin-nano selenium: 50 mM sodium selenite aqueous solution was stirred at 500 rpm at 60 ℃. The pH of the system was adjusted to 4.0~4.5. 400 mM vitamin C aqueous solution was added dropwise. The solution gradually turned red. 250 mM dihydromyricetin (60% ethanol solution) was added, and the mixture was stirred for 40 min. After cooling to room temperature, it was allowed to stand at 4 ℃ for 12 h. After centrifugation at 8000 rpm for 10 min, the supernatant was discarded, and the solution was washed with ultrapure water. The centrifugation was repeated 3 times. After freeze-drying, dihydromyricetin-nano selenium (DMY-SeNPs) was obtained. The obtained DMY-SeNPs were characterized as follows: Figure 1 As shown in (A), the UV-Vis absorption spectrum reveals that DMY-SeNPs simultaneously retain the characteristic absorption of DMY in the UV region and the broad absorption band of SeNPs in the visible region, indicating that DMY participates in the formation of selenium nanoparticles. Figure 1 As shown in (B), the FTIR results show that DMY-SeNPs exhibit absorption peak changes in characteristic regions such as —OH, C=C, and C—O, indicating that there is an interaction between the hydroxyl groups, aromatic structures, and oxygen-containing functional groups in the DMY molecule and SeNPs, which is beneficial to improving the stability of polyphenol-nano selenium. Figure 1 As shown in (C), the XRD patterns show that neither SeNPs nor DMY-SeNPs exhibited obvious sharp crystal diffraction peaks, but rather broad peaks overall, indicating that the obtained selenium nanoparticles are mainly amorphous. The crystallization peaks of DMY in DMY-SeNPs were significantly weakened, further indicating that the crystal order decreased after DMY was combined with SeNPs. Figure 1 (D) The particle size distribution results show that the particle size of SeNPs is mainly concentrated at around 100 nm, while the particle size of DMY-SeNPs is slightly larger and mainly distributed around 150 nm, indicating that composite nanoparticles are formed after DMY modification. Figure 1(EF) SEM images show that the obtained particles are nearly spherical with good dispersibility, and the surface morphology of DMY-SeNPs is relatively uniform. In summary, DMY can effectively participate in and stabilize the formation of selenium nanoparticles, and DMY-SeNPs composite nanoparticles with nanoscale particle size and regular morphology were successfully prepared, laying the foundation for their subsequent application as functional active ingredients in smart food preservation packaging materials.

[0047] (2) Optimization of synthesis conditions of dihydromyricetin-nano selenium The particle size of nanoparticles is an important indicator for evaluating the formation effect of dihydromyricetin-selenium nanoparticles. Particle size affects the dispersibility, stability, and uniform distribution of the complex in the film-forming solution and the packaging film matrix. Smaller and more stable nanoparticles are more easily and uniformly dispersed in the film matrix, reducing particle aggregation. Simultaneously, smaller particle size increases the specific surface area of ​​the particles, enhancing their contact opportunities with microbial cell surfaces, thus contributing to antibacterial effects. Therefore, this embodiment uses particle size as the primary evaluation indicator to optimize the preparation conditions of the dihydromyricetin-selenium nanoparticles using a single-factor approach.

[0048] like Figure 2 As shown, the molar ratio of sodium selenite to ascorbic acid, the molar ratio of sodium selenite to dihydromyricetin, the pH of the reaction system, the reaction temperature, and the reaction time all affect the particle size of the dihydromyricetin-selenocyanin nanocomposite. Figure 2 (A) It can be seen that when the molar ratio of sodium selenite to ascorbic acid is 1:8, the resulting complex has a smaller particle size; when the molar ratio is 1:10, the particle size increases significantly, indicating that excessive reducing agent dosage may lead to an overly rapid reduction reaction, increasing the possibility of particle aggregation. Figure 2 (B) It can be seen that when the molar ratio of sodium selenite to dihydromyricetin is 1:5, the particle size is smaller, while when the molar ratio is 1:6, the particle size increases. This indicates that an appropriate amount of dihydromyricetin is beneficial to stabilizing the nano-selenium particles, while an excessive amount may affect the particle dispersion state. Figure 2 (C) shows that the particle size is smaller at pH 4.0–4.5, while it increases significantly at pH 3.5 and 5.5, indicating that a suitable weakly acidic environment is conducive to the stable formation of the complex. Figure 2 (D) indicates that the particle size increases significantly at 70℃, suggesting that excessively high temperatures may promote particle growth or aggregation. Figure 2 (E) It can be seen that the particle size increases after the reaction time is extended to 70 min, indicating that an excessively long reaction time may lead to continued particle growth or secondary aggregation.

[0049] comprehensive Figure 2The results showed that the molar ratios of sodium selenite to ascorbic acid, sodium selenite to dihydromyricetin, pH, temperature, and reaction time all affected the particle size of the complex by influencing the reduction of selenium precursors, the nucleation and growth of selenium nanoparticles, and the particle stabilization process. Considering the particle size, particle dispersion stability, and suitability for use in food-grade active smart packaging films, the optimal preparation conditions for the dihydromyricetin-nano selenium complex were: a sodium selenite to ascorbic acid molar ratio of 1:8, a sodium selenite to dihydromyricetin molar ratio of 1:5, a reaction system pH of 4.0–4.5, a reaction temperature of 60℃, and a reaction time of 40 min.

[0050] Example 2: Antibacterial activity of dihydromyricetin-nano selenium Using common food spoilage bacteria as test subjects, and Staphylococcus aureus and Escherichia coli as representative species, the antibacterial activity of DMY-SeNPs was investigated. In one embodiment, a blank control group, a DMY group, a SeNPs group, and a DMY-SeNPs group were set up to compare the effects of different treatments on bacterial growth.

[0051] like Figure 3 As shown, DMY-SeNPs can inhibit bacterial growth, reduce colony count, or inhibit the increase of bacterial turbidity, demonstrating antibacterial activity. Compared with dihydromyricetin or nano-selenium alone, DMY-SeNPs exhibit better overall antibacterial effects and are suitable for introduction into food packaging films as active preservatives.

[0052] Example 3: Preparation of a bilayer membrane containing 2% polyphenol-nano selenium like Figure 4As shown, the basic film-forming solution was first prepared. 2.50 g of gelatin was weighed and added to 50 mL of deionized water, and heated and stirred at 50 °C until completely dissolved. Separately, 0.25 g of κ-carrageenan was weighed and added to 50 mL of deionized water, and heated and stirred at 90 °C until completely dissolved. Equal volumes of the gelatin and κ-carrageenan solutions were mixed to obtain a mixed film-forming solution with a final gelatin concentration of 2.5% and a final κ-carrageenan concentration of 0.25%. At this point, the total dry weight of gelatin and κ-carrageenan was 2.75 g. Subsequently, 1.10 g of glycerol was added to the mixed film-forming solution, representing 40% of the dry weight, and stirring was continued for 10 min to obtain the basic film-forming solution. An active film-forming solution containing DMY-SeNPs was then prepared. Based on a DMY-SeNPs addition amount of 2% by dry weight, 0.055 g of DMY-SeNPs was weighed and added to 100 mL of the above-mentioned basic film-forming solution. The solution was stirred and ultrasonically dispersed to obtain a basic film-forming solution containing 2% DMY-SeNPs. A pH-indicating film-forming solution containing anthocyanins was prepared. Based on a pH of 1.25% by dry weight, 0.0344 g of anthocyanins was weighed and added to 100 mL of the basic film-forming solution. The solution was stirred in the dark until uniformly dispersed to obtain a basic film-forming solution containing anthocyanins, which was used to form a local pH-indicating zone. A circular mold (occupying 4% of the total area) was placed on a horizontal film-forming carrier with a diameter of 90 mm. 15 mL of the basic film-forming solution containing 2% DMY-SeNPs was poured onto the film-forming carrier to form the inner layer membrane. After pouring, the solution was allowed to stand at room temperature for about 30 minutes to allow the inner layer membrane to form a gel. The circular mold was then removed, leaving a circular reserved area in the inner layer membrane. Anthocyanin-containing base film-forming solution was added to the circular reserved area and allowed to stand at room temperature for about 30 minutes to form a local pH indicator zone. It was then dried at 40 °C for 4 hours. Finally, 8 mL of the base film-forming solution was uniformly coated onto the upper surface of the inner membrane and dried at 40 °C for 4 hours to obtain a bilayer active smart membrane with a local pH indicator zone.

[0053] The composite preservation film prepared in this embodiment was used for membrane performance characterization and cold meat preservation experiments.

[0054] Comparative Example 1: Blank Treatment Group Fresh meat samples of the same specifications as those used in the preservation experiment of Example 3 were taken and subjected to preservation experiments under the same storage conditions without any packaging film treatment. This comparative example is only used for fresh meat preservation experiments and does not involve membrane performance characterization.

[0055] Comparative Example 2: Bilayer membrane without polyphenols and nano-selenium The difference from Example 3 is that no polyphenol-nano selenium is added to the film-forming solution, which is used for membrane performance characterization and cold meat preservation experiments.

[0056] Comparative Example 3: Bilayer membrane assembly containing 1% polyphenol-nano selenium The difference from Example 3 is that 1% polyphenol-nano selenium was added to the film-forming solution for membrane performance characterization and cold meat preservation experiments.

[0057] Comparative Example 4: Bilayer membrane assembly containing 3% polyphenol-nano selenium The difference from Example 3 is that 3% polyphenol-nano selenium was added to the film-forming solution for membrane performance characterization and cold meat preservation experiments.

[0058] Comparative Example 5: Ordinary polyethylene film assembly Fresh meat samples of the same specifications as those used in the preservation experiment of Example 3 were taken, treated with polyethylene film, and subjected to preservation experiments under the same storage conditions. This comparative example is only used for fresh meat preservation experiments and does not involve membrane performance characterization.

[0059] Test Example 1: Membrane Performance Characterization Figure 5 The optical properties, structural features, hydrophilicity and hydrophobicity, barrier properties and mechanical properties of the membranes with different treatment groups were demonstrated.

[0060] Depend on Figure 5 (A) As can be seen, there are significant differences in the UV-Vis transmittance of the films in different treatment groups. Comparative Example 2 has a higher transmittance in the visible light region, indicating better transparency, but relatively weaker light blocking ability. With changes in treatment level, the transmittance of Comparative Example 3, Example 3, and Comparative Example 4 generally decreases, indicating that the film's light-shielding ability is enhanced. (Combined with...) Figure 5 (D) As can be seen, the opacity shows an opposite trend, with Comparative Example 4 exhibiting the highest opacity, indicating its strongest light-blocking ability. However, excessively high opacity may affect the direct observation of the beef's color and surface condition during the packaging process. Therefore, optical performance is not necessarily better the lower the transmittance, but rather requires a balance between light blocking and the visibility of the contents.

[0061] like Figure 5 (B) and Figure 5 As shown in (C), the infrared spectra and X-ray diffraction patterns of the films in different treatment groups showed little overall difference. Figure 5 In (B), all groups of membranes exhibited similar main characteristic absorption peaks, including characteristic peaks of NH stretching vibration, Amide II and CO, indicating that different treatments did not significantly change the main chemical functional group structure of the membrane material. Figure 5 In (C), all groups of films exhibited broad diffraction peaks without any obvious new sharp characteristic peaks, indicating that the films as a whole still mainly consist of an amorphous or low-crystallinity structure, and no obvious new crystalline phases or large-sized crystal aggregates were formed after treatment. The above results show that different treatments mainly change the physical properties of the films while maintaining the stability of the main structure, rather than achieving performance differences by significantly altering the chemical or crystal structure of the films.

[0062] The results for moisture content and water contact angle are shown below. Figure 5 (E) and Figure 5 (F). Figure 5 (E) shows that Comparative Example 2 has a higher moisture content, while the moisture content of Comparative Example 3, Example 3 and Comparative Example 4 gradually decreases, indicating that the membrane's sensitivity to moisture decreases. Figure 5 (F) shows that the water contact angle increases with increasing treatment level, indicating enhanced hydrophobicity of the membrane surface. The decrease in moisture content and the increase in water contact angle indicate that the membrane's ability to adsorb and wet moisture is weakened. This is beneficial for reducing the impact of moisture on the membrane's structural stability during packaging and also helps improve the membrane's suitability in high-humidity food packaging environments.

[0063] Figure 5 (G) and Figure 5 (H) represents water vapor transmission rate and oxygen transmission rate, respectively. The results show that Comparative Example 2 has higher water vapor transmission rate and oxygen transmission rate, indicating relatively weaker barrier properties. Comparative Examples 3, 3, and 4 all show a decreasing trend in water vapor transmission rate and oxygen transmission rate, indicating that the membrane structure gradually becomes denser, and the diffusion paths of water vapor and oxygen within the membrane are prolonged. For meat packaging, lower water vapor transmission rate helps reduce moisture migration, while lower oxygen transmission rate helps slow down oxidation reactions and microbial growth. Therefore, improving barrier properties is crucial for subsequent preservation effects.

[0064] Mechanical property results as follows Figure 5 As shown in (I), the tensile strength of the membrane gradually increases with the change in treatment level, indicating that the membrane's ability to resist external tensile forces is enhanced. This may be related to the more compact internal structure of the membrane. However, the elongation at break shows a decreasing trend, indicating that the membrane's flexibility gradually decreases. Although Comparative Example 4 has the highest tensile strength, it has the lowest elongation at break, indicating that the membrane material tends to be rigid and may be more prone to brittleness during actual packaging, folding, sealing, and transportation.

[0065] comprehensive Figure 5(A–I) shows that Comparative Example 2 has good transparency and stretchability, but insufficient light blocking, hydrophobicity, and barrier properties. Comparative Example 3 is an improvement over Comparative Example 2, but the overall improvement is limited. Comparative Example 4 shows strong performance in light blocking, hydrophobicity, water vapor barrier, oxygen barrier, and tensile strength, but also exhibits problems of excessively high opacity and a significant decrease in elongation at break. In contrast, Example 3, while maintaining the stability of the main film structure, combines good light blocking ability, moderate opacity, low moisture content, high water contact angle, good water vapor and oxygen barrier properties, and a relatively balanced tensile strength and elongation at break. Therefore, from the perspective of the comprehensive application performance of the film material, Example 3 achieves a more reasonable balance between transparency, barrier properties, hydrophobicity, strength, and flexibility, and is more suitable as a treatment group for food preservation packaging film.

[0066] Test Example 2: Fresh Meat Preservation Experiment The pH change results are as follows: Figure 6 As shown in (A), the pH of beef in all groups increased with prolonged storage time, which is related to the decomposition of proteins and nitrogenous substances and the accumulation of alkaline metabolites during meat storage. Comparative Example 1 showed a larger pH increase, indicating a faster spoilage process. Comparative Examples 2 and 5 also showed higher pH levels in the later stages, indicating a limited effect on slowing down the spoilage process. Comparative Examples 3, 3, and 4 showed relatively slower pH increases, suggesting that these treatments could inhibit the accumulation of alkaline spoilage products to some extent.

[0067] Changes in total bacterial count are shown in Figure 6 (B) The total bacterial count varied little among the groups in the early stages of storage, but gradually increased with prolonged storage. Comparative Examples 1, 2, and 5 showed faster growth in total bacterial count during the later stages of storage, indicating significant microbial proliferation. Comparative Examples 3, 3, and 4 had relatively low total bacterial counts, suggesting that these treatments had a certain inhibitory effect on microbial growth. Microbial proliferation is a major cause of meat spoilage; therefore, a reduction in total bacterial count directly reflects the improvement in the preservation effect of packaging treatment on beef.

[0068] Changes in TVB-N content, such as Figure 6 (C) shows that TVB-N is an important indicator for evaluating the degradation and spoilage of meat proteins. With prolonged storage, the TVB-N content in all groups gradually increased, but at different rates. Comparative Example 1 showed the most significant increase, indicating rapid protein decomposition and accumulation of spoilage products; Comparative Examples 2 and 5 also showed high levels of TVB-N accumulation. Comparative Examples 3, 3, and 4 had relatively low TVB-N contents, indicating that membrane treatment can delay the production of volatile basic nitrogen in beef, thereby slowing down the spoilage process.

[0069] Changes in MDA content are shown in [the table]. Figure 6 (D). MDA is an important product of lipid oxidation and can reflect the degree of oxidation in beef during storage. The MDA content in all groups increased with time, indicating that lipid oxidation continued. Comparative Examples 1, 2, and 5 showed higher MDA content, indicating a weaker inhibitory effect on lipid oxidation. Comparative Examples 3, 3, and 4 showed relatively lower MDA accumulation, suggesting that these treatments could slow down the lipid oxidation reaction. Figure 5 Based on the results of the medium barrier performance, the reduced water vapor and oxygen permeability may help reduce the amount of oxygen entering the packaging system, thereby delaying the oxidation reaction.

[0070] Figure 7 The membrane color response and its relationship with beef quality indicators are demonstrated. Figure 7 (A) It can be seen that as the storage time is extended, the color of each group of membranes changes to different degrees, indicating that the membrane can respond to changes in beef quality. Figure 7 (C–F) shows that ΔE, L*, a*, and b* values ​​all change during storage, with ΔE reflecting the overall color difference and used to characterize the degree of membrane color response. Figure 7 (B) Further analysis shows that ΔE is positively correlated with pH, ​​TVB-N, total bacterial count, and MDA, while a* value is negatively correlated with these quality indicators, indicating a strong correlation between membrane color changes and beef spoilage indicators. In other words, membrane color changes are not simply a change in appearance, but can reflect the process of beef freshness decline to a certain extent.

[0071] comprehensive Figure 6 , 7 It can be seen that the beef in Comparative Example 1 deteriorated the fastest, indicating that the blank treatment could not effectively delay spoilage; the preservation effects of Comparative Examples 2 and 5 were limited; Comparative Example 3 showed some improvement over Comparative Example 2; Comparative Example 4 performed better in some preservation indicators, but combined with... Figure 5 It is evident that the membrane material exhibits issues of high opacity and reduced flexibility. Example 3 demonstrates superior overall performance in terms of pH control, total bacterial count inhibition, delayed TVB-N accumulation, MDA formation inhibition, and color response. Furthermore, its membrane performance does not show the significant loss of transparency and stretchability seen in Comparative Example 4. Therefore, considering both preservation effect and practical packaging application, Example 3 is a more reasonable treatment group, effectively balancing active preservation and intelligent indication functions.

[0072] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a plant polyphenol-composite selenium nano-state active smart food preservation film, characterized in that, Includes the following steps: S1. Polyphenol-selenium composite nanoparticles are formed by combining polyphenols and selenium compounds. S2. Add polyphenol-selenium composite nanoparticles to the basic film-forming solution at 1%~3% of the dry matter mass of the basic film-forming solution and mix evenly to obtain the inner active film-forming solution. S3. Add the anthocyanin solution or anthocyanin-rich extract to the base film-forming solution and mix well to obtain a pH-indicating film-forming solution. S4. The inner layer active film-forming liquid is poured into the film-forming carrier and left to stand until the inner layer active film-forming liquid forms a gel. The film-forming carrier has a mold for forming a reserved indicator area, and the area of ​​the mold accounts for 2% to 5% of the area of ​​the film-forming carrier. S5. Remove the mold, add pH indicator film-forming solution to the reserved indicator area, let stand until the pH indicator film-forming solution forms a gel, and dry to form a film to obtain an inner active indicator film with a local pH indicator area. S6. A basic film-forming solution is uniformly coated on the surface of the inner active indicator membrane, and then dried again to form a film, thus obtaining a double-layer active smart membrane with a local pH indicator area.

2. The preparation method according to claim 1, characterized in that, The selenium compound is one or more of inorganic selenium, selenoamino acids, selenopeptides, and selenoproteins.

3. The preparation method according to claim 2, characterized in that, The polyphenol-selenium composite nanoparticles can be prepared by the following method: S01. Stir the aqueous solution of 40-60 mM selenium compound at 50-60 °C to adjust the pH of the system to 4.0-4.5; S02. Add ascorbic acid aqueous solution dropwise to the aqueous solution of selenium compound in S01, then add polyphenol solution, stir and react for 40-60 min, cool and let stand, centrifuge to remove supernatant, wash and dry to obtain polyphenol-selenium composite nanoparticles; wherein, the molar ratio of selenium compound to ascorbic acid is 1:7-9, and the molar ratio of selenium compound to polyphenol is 1:4.5-5.

5.

4. The preparation method according to claim 1, characterized in that, The basic film-forming solution is composed of gelatin, κ-carrageenan, glycerol and water; wherein the concentration of the gelatin solution is 1%~2.5%, the concentration of the κ-carrageenan solution is 0.2%~0.5%, and the amount of glycerol added is 25%~40% of the total dry weight of the film-forming solution.

5. The preparation method according to claim 1, characterized in that, The polyphenols are one or more of dihydromyricetin, silymarin, quercetin, resveratrol, curcumin, and puerarin.

6. The preparation method according to claim 1, characterized in that, The anthocyanins are added at 0.75% to 1.5% of the dry matter mass of the base film-forming solution, and the anthocyanins are derived from one or more of the following: blueberries, purple sweet potatoes, purple cabbage, black goji berries, mulberries, black rice, or grape skins.

7. The preparation method according to claim 1, characterized in that, In step S6, a basic film-forming solution is uniformly coated on the surface of the inner active indicator membrane as an outer basic protective membrane layer. The volume ratio of the inner active film-forming solution to the film-forming solution of the outer basic protective membrane layer is 1.5~2.5:

1.

8. The preparation method according to claim 1, characterized in that, The film is dried at 35-45℃ for 3-5 hours.

9. A bilayer active smart membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the double-layer active smart film according to claim 9 in food preservation.

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