Multifunctional water-absorbing composite preservative pad, preparation method and application thereof

Abstract

The application discloses a multifunctional water-absorbing composite fresh-keeping pad, which is prepared by uniformly dispersing iron-based metal organic framework material Ant@Fe-MOFs loaded with anthocyanin in a methyl cellulose-sodium alginate MC-SA composite hydrogel matrix to obtain the multifunctional water-absorbing composite fresh-keeping pad MC-SA-Ant@Fe-MOFs. The multifunctional composite fresh-keeping pad MC-SA-Ant@Fe-MOFS with high water absorption, significant antibacterial property, strong antioxidant property, intelligent pH response release and freshness visual indication is successfully prepared by uniformly dispersing the iron-based metal organic framework material Ant@Fe-MOFs loaded with anthocyanin in the methyl cellulose-sodium alginate MC-SA composite hydrogel matrix. The composite fresh-keeping pad has excellent biocompatibility and safety, and through comprehensive physical water absorption, antibacterial and antioxidant properties and intelligent controlled release, the corruption and deterioration of pork are significantly delayed, the fresh-keeping effect of meat is improved, and the shelf life of meat is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of fresh meat preservation technology, specifically relating to a multifunctional absorbent composite preservation pad, its preparation method, and its application. Background Technology

[0002] High-value animal protein products such as fresh meat, poultry, and fish are highly susceptible to microbial contamination (such as Escherichia coli and Staphylococcus aureus) and enzymatic degradation during storage and transportation due to their high moisture and nutrient content. This can lead to juice loss, color deterioration, and rancidity, seriously threatening food safety.

[0003] Traditional preservation technologies, such as freezing, the addition of chemical preservatives, and modified atmosphere packaging, while widely used, have significant limitations: freezing consumes a lot of energy and affects texture; the addition of chemical preservatives (such as nitrites) contradicts the current consumer trend of "clean labels." Therefore, developing natural active packaging materials that combine high water absorption and active antibacterial and antioxidant functions has become a research hotspot.

[0004] Among novel food preservation materials, hydrogels, due to their three-dimensional network structure and high water content, have become ideal substrates for moisture-absorbing and preservative pads. Sodium alginate (SA) and methylcellulose (MC) are commonly used natural polymers. While sodium alginate (SA) can form a mild gel through ionic crosslinking, its single gel often exhibits poor mechanical strength, is prone to dehydration and shrinkage, and its water absorption capacity decreases after long-term storage. Methylcellulose (MC), although possessing thermogel properties, often requires heating for molding when used alone and has relatively insufficient water retention. Combining SA and MC can synergistically improve these shortcomings. Utilizing the ionic crosslinking network of SA and the physical entanglement / thermogel properties of MC, a composite hydrogel matrix (MC-SA) with both high mechanical strength and ultra-high water absorption / retention properties can be constructed, serving as a physical barrier and juice absorption layer.

[0005] However, pure SA / MC composite hydrogels (MC-SA) mainly play a passive water absorption role, with almost zero antibacterial / antioxidant capabilities, and cannot actively inhibit the proliferation of microorganisms on food surfaces. Therefore, researchers have attempted to introduce natural antibacterial agents.

[0006] Anthocyanins, as a class of natural polyphenolic compounds, have excellent antioxidant and antibacterial activities, but their unstable chemical properties (easily degraded by pH, temperature and light), easy burst release when added directly, and low bioavailability severely limit their long-term application in food preservation pads.

[0007] To overcome the instability and controlled release issues of anthocyanins, carrier materials are needed. Metal-organic frameworks (MOFs) have shown great potential in the field of active substance encapsulation and controlled release due to their ultra-high specific surface area and tunable pore structure. Summary of the Invention

[0008] Therefore, the purpose of this invention is to provide a multifunctional absorbent composite food preservation pad, its preparation method, and its application, so as to overcome the technical problems existing in the above-mentioned existing composite hydrogels MC-SA.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: The first aspect of the present invention is to provide a multifunctional absorbent composite food preservation mat, which uses methylcellulose-sodium alginate MC-SA as a composite hydrogel matrix, and uniformly disperses anthocyanin-loaded iron-based metal-organic framework material Ant@Fe-MOFs in the composite hydrogel matrix to obtain the multifunctional absorbent composite food preservation mat MC-SA-Ant@Fe-MOFs.

[0010] A second aspect of the present invention is to provide a method for preparing a multifunctional absorbent composite food preservation pad, comprising the following steps: (1) Preparation of composite hydrogel matrix Sodium alginate powder (SA) was dissolved in a deionized solution to prepare a sodium alginate dispersion. Methylcellulose (MC) was dispersed in preheated deionized water and heated and stirred until completely dissolved to prepare a methylcellulose dispersion. The sodium alginate dispersion and the methylcellulose dispersion were mixed and stirred evenly to obtain a mixed solution. A crosslinking agent was added to the mixed solution and stirred evenly to obtain a composite hydrogel matrix MC-SA with a preliminary gel network. (2) Preparation of anthocyanin-loaded iron-based metal-organic framework composites 2,5-Dihydroxyterephthalic acid and 2-aminoterephthalic acid were dissolved in methanol to prepare a first solution. Imidazole organic ligands were dissolved in methanol, and anthocyanin Ant was added and stirred until completely dissolved to prepare a second solution. Iron salts were dissolved to obtain a third solution. The first, second, and third solutions were mixed, stirred evenly, centrifuged, and the precipitate was collected. After washing and drying, anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs was obtained. (3) Preparation of composite hydrogel absorbent pad The anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs was added to the composite hydrogel matrix MC-SA and ultrasonically mixed to obtain a film-forming solution. After film formation and drying, the composite hydrogel absorbent pad MC-SA-Ant@Fe-MOFs was obtained.

[0011] In an optional embodiment, in step (1), the concentration of sodium alginate dispersion is 2-4% w / v; the concentration of methylcellulose dispersion is 1-3% w / v.

[0012] In an optional embodiment, in step (2), the mass ratio of 2,5-dihydroxyterephthalic acid to 2-aminoterephthalic acid is 1:1.

[0013] In an optional embodiment, in step (2), the imidazole organic ligand is 2-methylimidazole, and the mass ratio of the iron salt, 2-methylimidazole and anthocyanin is (7-12):(5-10):(3-7).

[0014] In an optional embodiment, in step (3), the anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs accounts for 1 to 5% of the total solid mass of the composite hydrogel matrix MC-SA.

[0015] In an optional embodiment, in step (1), the crosslinking agent is an anhydrous calcium chloride solution or citric acid solution with a mass fraction of 1 to 5%.

[0016] In one alternative embodiment, in step (3), the power of the ultrasonic treatment is 100-150W and the time is 30-45min.

[0017] In one alternative embodiment, in step (3), the film-forming process involves casting the film-forming solution onto a mold and drying it at a temperature of 40–50°C for 36–48 hours.

[0018] A third aspect of the present invention is to provide an application of a multifunctional absorbent composite preservation mat in the preservation of chilled meat.

[0019] Compared with the prior art, the technical solution of the present invention has the following advantages: This invention successfully prepared a multifunctional composite preservation mat, MC-SA-Ant@Fe-MOFS, by uniformly dispersing anthocyanin-loaded iron-based metal-organic framework material Ant@Fe-MOFs in a methylcellulose-sodium alginate (MC-SA) composite hydrogel matrix. This mat possesses high water absorption, significant antibacterial properties, strong antioxidant effects, and intelligent pH-responsive release with visual indication of freshness. The composite preservation mat exhibits excellent biocompatibility and safety. Through comprehensive physical water absorption, antibacterial and antioxidant properties, and intelligent controlled release, it significantly delays the spoilage of pork, improves the preservation effect of meat, and extends its shelf life. Attached Figure Description

[0020] Figure 1 The images show the SEM morphology of the Fe-MOFs and Ant@Fe-MOFs of this invention. Figure 2 The FTIR spectra of Fe-MOFs and Ant@Fe-MOFs of this invention are shown below. Figure 3The XRD spectra of Fe-MOFs and Ant@Fe-MOFs of this invention are shown below. Figure 4 SEM images and elemental distribution diagrams of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 5 The FTIR spectra of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown below. Figure 6 The XRD patterns of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown below. Figure 7 The results of water absorption performance tests for the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 8 The results of water retention performance tests for the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are as follows: Figure 9 The swelling performance test results of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 10 The results of water contact angle tests for the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of this invention are as follows: Figure 11The antibacterial test results are for the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention. Figure 12 The results of DPPH free radical scavenging tests on the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 13 The results of ABTS free radical scavenging tests on the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 14 The biocompatibility test results of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention are shown. Figure 15 The results of color change tests of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention at different pH values ​​during pork preservation are shown. Figure 16 The results of the polyphenol release rate test of the composite hydrogel pad MC-SA-Ant of the present invention at different pH values ​​are shown. Figure 17 The results of the polyphenol release rate test of the composite hydrogel pad MC-SA-Ant@ZIF-8 of the present invention at different pH values ​​are shown. Figure 18 The results of polyphenol release rate tests on the composite hydrogel pad MC-SA-Ant@Ag-MOFs of this invention at different pH values ​​are shown. Figure 19 The results of polyphenol release rate tests on the composite hydrogel pad MC-SA-Ant@Fe-MOFs of this invention at different pH values ​​are shown. Figure 20The present invention describes the appearance changes of pork during the preservation process using composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs. Figure 21 The effects of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention on the total sulfur content of pork during the preservation process; Figure 22 The effects of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention on the carbonyl content of pork during the preservation process; Figure 23 The effects of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention on the TVB-N value of pork during the preservation process; Figure 24 The effects of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention on the TBARS value of pork during the preservation process; Figure 25 The effects of the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs of the present invention on the total viable bacteria count (TVC) during pork storage. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0022] Example 1 A multifunctional absorbent composite food preservation mat is prepared by the following steps: 1) Preparation of composite hydrogel matrix: Sodium alginate (SA) powder was slowly added to deionized water and stirred until completely dissolved to prepare a homogeneous sodium alginate dispersion with a mass-volume concentration of 3%; methylcellulose (MC) powder was dispersed in preheated (approximately 60-80℃) deionized water, stirred until dissolved, and then cooled to room temperature to prepare a methylcellulose dispersion with a mass-volume concentration of 2%; the sodium alginate dispersion and the methylcellulose dispersion were mixed at a mass ratio of 1:1 and stirred evenly to obtain an MC-SA mixed solution; an anhydrous calcium chloride solution with a mass fraction of 2% was added to the mixed solution and stirred evenly to obtain a composite hydrogel matrix MC-SA with a preliminary gel network.

[0023] 2) Preparation of anthocyanin-loaded iron-based metal-organic framework composites: 10 mg of 2,5-dihydroxyterephthalic acid and 10 mg of 2-aminoterephthalic acid were dissolved in 5 mL of methanol to prepare the first solution. 5 mg of anthocyanin was added to 1 mL of methanol solution containing 8 mg of 2-methylimidazole and stirred until completely dissolved to prepare the second solution. 9 mg of ferric chloride was dissolved in 0.5 mL of methanol to obtain the third solution. The first, second, and third solutions were mixed and stirred vigorously at room temperature for 2 h. Then, the mixture was centrifuged to separate the precipitate. The precipitate was thoroughly washed three times with water to obtain the anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs.

[0024] 3) Preparation of composite hydrogel absorbent pad: Ant@Fe-MOFs, anthocyanin-loaded iron-based metal-organic framework composite material, is added to the composite hydrogel matrix MC-SA. The anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs accounts for 2% of the total solid mass of the composite hydrogel matrix MC-SA. The mixture is ultrasonically mixed to obtain a film-forming solution. The film-forming solution is cast into a flat mold (such as a petri dish or a container of a specific shape). The mold is placed in a forced-air drying oven and dried at 40-50°C for 48 hours until the moisture is completely evaporated, forming a self-supporting composite hydrogel film with a porous network structure. The dried film is peeled off from the mold and cut into specific sizes according to application requirements to obtain the composite hydrogel absorbent pad MC-SA-Ant@Fe-MOFs.

[0025] Example 2 A multifunctional absorbent composite food preservation mat is prepared by the following steps: 1) Preparation of composite hydrogel matrix: Sodium alginate (SA) powder was slowly added to deionized water and stirred until completely dissolved to prepare a homogeneous sodium alginate dispersion with a mass-volume concentration of 2%; methylcellulose (MC) powder was dispersed in preheated (approximately 60-80℃) deionized water, stirred until dissolved, and then cooled to room temperature to prepare a methylcellulose dispersion with a mass-volume concentration of 3%; the sodium alginate dispersion and the methylcellulose dispersion were mixed at a mass ratio of 1:2 and stirred evenly to obtain an MC-SA mixed solution; a crosslinking agent anhydrous calcium chloride solution with a mass fraction of 2% was added to the mixed solution and stirred evenly to obtain a composite hydrogel matrix MC-SA with a preliminary gel network.

[0026] 2) Preparation of anthocyanin-loaded iron-based metal-organic framework composites: 10 mg of 2,5-dihydroxyterephthalic acid and 10 mg of 2-aminoterephthalic acid were dissolved in 5 mL of methanol to prepare the first solution. 7 mg of anthocyanin was added to 1 mL of methanol solution containing 10 mg of 2-methylimidazole and stirred until completely dissolved to prepare the second solution. 7 mg of ferric chloride was dissolved in 0.5 mL of methanol to obtain the third solution. The first, second, and third solutions were mixed and stirred vigorously at room temperature for 2 h. Then, the mixture was centrifuged to separate the precipitate. The precipitate was thoroughly washed three times with water to obtain the anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs.

[0027] 3) Preparation of composite hydrogel absorbent pad: Ant@Fe-MOFs, anthocyanin-loaded iron-based metal-organic framework composite material, is added to the composite hydrogel matrix MC-SA. The anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs accounts for 5% of the total solid mass of the composite hydrogel matrix MC-SA. The mixture is ultrasonically mixed to obtain a film-forming solution. The film-forming solution is cast into a flat mold (such as a petri dish or a container of a specific shape). The mold is placed in a forced-air drying oven and dried at 40-50°C for 48 hours until the moisture is completely evaporated, forming a self-supporting composite hydrogel film with a porous network structure. The dried film is peeled off from the mold and cut into specific sizes according to application requirements to obtain the composite hydrogel absorbent pad.

[0028] Example 3 A multifunctional absorbent composite food preservation mat is prepared by the following steps: 1) Preparation of composite hydrogel matrix: Sodium alginate (SA) powder was slowly added to deionized water and stirred until completely dissolved to prepare a homogeneous sodium alginate dispersion with a mass-volume concentration of 4%; methylcellulose (MC) powder was dispersed in preheated (approximately 60-80℃) deionized water, stirred until dissolved, and then cooled to room temperature to prepare a methylcellulose dispersion with a mass-volume concentration of 3%; the sodium alginate dispersion and the methylcellulose dispersion were mixed at a mass ratio of 1:2 and stirred evenly to obtain an MC-SA mixed solution; 2% (by mass) of anhydrous calcium chloride solution as a crosslinking agent was added to the mixed solution and stirred evenly to obtain a composite hydrogel matrix MC-SA with a preliminary gel network.

[0029] 2) Preparation of anthocyanin-loaded iron-based metal-organic framework composites: 10 mg of 2,5-dihydroxyterephthalic acid and 10 mg of 2-aminoterephthalic acid were dissolved in 5 mL of methanol to prepare the first solution. 3 mg of anthocyanin was added to 1 mL of methanol solution containing 6 mg of 2-methylimidazole and stirred until completely dissolved to prepare the second solution. 10 mg of ferric chloride was dissolved in 0.5 mL of methanol to obtain the third solution. The first, second, and third solutions were mixed and stirred vigorously at room temperature for 2 h. Then, the mixture was centrifuged to separate the precipitate. The precipitate was thoroughly washed three times with water to obtain the anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs.

[0030] 3) Preparation of composite hydrogel absorbent pad: Ant@Fe-MOFs, anthocyanin-loaded iron-based metal-organic framework composite material, is added to the composite hydrogel matrix MC-SA. The anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs accounts for 3% of the total solid mass of the composite hydrogel matrix MC-SA. The mixture is ultrasonically mixed to obtain a film-forming solution. The film-forming solution is cast into a flat mold (such as a petri dish or a container of a specific shape). The mold is placed in a forced-air drying oven and dried at 40-50°C for 48 hours until the moisture is completely evaporated, forming a self-supporting composite hydrogel film with a porous network structure. The dried film is peeled off from the mold and cut into specific sizes according to application requirements to obtain the composite hydrogel absorbent pad.

[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that it does not contain iron-based organometallic frameworks (Fe-MOFs), and anthocyanins (Ant) are dispersed in the composite hydrogel matrix MC-SA to obtain the composite hydrogel absorbent pad MC-SA-Ant.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that it does not contain anthocyanin Ant. Iron-based organometallic frameworks (Fe-MOFs) are dispersed in a composite hydrogel matrix (MC-SA) to obtain a composite hydrogel absorbent pad MC-SA@Fe-MOFs.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that Ant@Fe-MOFs in step (2) is replaced with Ant@ZIP-8, while the rest of the process is the same as in Example 1, to prepare CS-SA-Ant@ZIP-8. The specific preparation process of Ant@ZIP-8 is as follows: 150 mg Zn(NO3)2·H2O was dissolved in 5 mL of deionized water, and 330 mg 2-MIM was dissolved in 10 mL of methanol. 5 mg of anthocyanin Ant was dissolved in the 2-MIM methanol solution. The two solutions were mixed and stirred at 200 rpm, then centrifuged at 10,000 rpm for 10 minutes to collect the precipitate. The precipitate was washed three times with methanol to remove the encapsulated anthocyanins, and then vacuum dried at 24°C for 12 hours to obtain anthocyanin Ant-encapsulated Ant@ZIF-8.

[0034] Comparative Example 4 The difference between this comparative example and Example 1 is that Ant@Fe-MOFs in step (2) is replaced with Ant@Ag-MOFs, while the rest of the process is the same as in Example 1, to prepare CS-SA-Ant@Ag-MOFs. The specific preparation process of Ant@Ag-MOFs is as follows: 0.6 g AgNO3 was dissolved in 90 mL of deionized water, 1.05 g 2-MIM was dissolved in 90 mL of ethanol, and 5 mg anthocyanin was dissolved in the 2-MIM ethanol solution. The two solutions were mixed and stirred for 15 minutes, followed by sonication for 2 minutes. The mixture was then centrifuged at 10,000 rpm for 10 minutes to collect the precipitate. Finally, the synthesized Ant@Ag-MOFs were collected, thoroughly washed with ethanol and water, and dried overnight in a preheated (45 °C) oven to obtain anthocyanin Ant-encapsulated Ant@Ag-MOFs.

[0035] Effect verification

[0036] I. Characterization of MOFs and Ant@MOFs

[0037] The microstructure of Fe-MOFs and Ant@Fe-MOFs composite particles loaded with Ant was characterized.

[0038] (a) Scanning Electron Microscopy (SEM) Characterization was performed using scanning electron microscopy (SEM), and the results are as follows: Figure 1As shown, Fe-MOFs and Ant@Fe-MOFs exhibit Fe... 3+ The morphology of nanoparticles with ionic characteristics. The results show that metal ions significantly affect the morphological characteristics of MOFs. In addition, the encapsulation of Ant by Fe-MOFs does not change its framework structure, indicating that Fe-MOFs can encapsulate anthocyanin (Anthocyanin).

[0039] (II) Fourier Transform Infrared Spectroscopy (FTIR) Analysis The samples were tested using Fourier transform infrared spectroscopy (FTIR) (Nicolet IS5, Thermo Fisher, USA), with a spectral acquisition range of 400 to 4000 cm⁻¹. -1 The resolution is 4 cm. -1 Each sample was scanned 32 times. The results are as follows: Figure 2 As shown in the figure.

[0040] As can be observed from the figure, Ant@Fe-MOFs exhibits the characteristic peaks of Fe-MOFs, while the characteristic peaks of Ant are masked. This phenomenon indicates that the binding mode of Ant to Fe-MOFs is not surface adsorption, but rather embedding within them, leading to the disappearance of Ant's characteristic peaks.

[0041] (III) X-ray diffraction (XRD) analysis The XRD patterns of the samples were determined using an X-ray powder diffractometer (D8 Advance, Bruker, Germany) at 40 kV and 40 mA, in the 2θ region from 5° to 60°, with a scan rate of 0.02° / min. The results are as follows: Figure 3 As shown.

[0042] As shown in the figure, the spectrum exhibits narrow and sharp peaks, confirming its unique crystal structure. Furthermore, Fe-MOFs retain their respective characteristic peaks after binding Ant, while masking the characteristic peaks of Ant at 12.7, 21.8, and 23.7 nm. This further demonstrates that Fe-MOFs can encapsulate Ant through binding without disrupting their own structure.

[0043] (iv) Determination of specific surface area and pore size The specific surface area and pore volume of the samples were determined using a BET surface area and pore size analyzer (ASAP2460, Micromeriti SA, USA) at 77 K using the N2 adsorption-desorption isotherm method. Before analysis, all samples were degassed at 80 °C for 4 hours to remove surface adsorbates. The specific surface area of ​​each MOF group is shown in Table 1.

[0044] Table 1 BET data for Fe-MOFs and Ant@Fe-MOFs

[0045] The results showed that the specific surface area of ​​Fe-MOFs was 1783.6864 m². 2 / g. After encapsulation with anthocyanins (Ant), the specific surface area is 1132.4870 m². 2 The specific surface area, pore volume, and pore size decreased by 36.51% compared to the original value. Furthermore, the pore volume of Ant@Fe-MOFs was 1.1295 ml / g, corresponding to a pore size of 1.9448 nm. The encapsulation of anthocyanins in Fe-MOFs resulted in a decrease in specific surface area, pore volume, and pore size. This is mainly due to the anthocyanins occupying the internal space of the MOFs, confirming that anthocyanins were successfully encapsulated in Fe-MOFs.

[0046] II. Characterization of the composite hydrogel pad In the following tests, unless otherwise specified, the composite hydrogel pads MC-SA, MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, and MC-SA-Ant@Fe-MOFs prepared in Example 1 and Comparative Examples 1-4 were used as the test samples.

[0047] (a) Scanning Electron Microscopy (SEM) The samples were observed using scanning electron microscopy (SEM), and their elemental composition was analyzed using energy-dispersive X-ray spectroscopy (EDS; Xplore 30, Oxford Instruments, UK). The results are as follows: Figure 4 As shown in the figure, all hydrogels exhibit an interconnected porous structure, which forms a network structure through polymer self-assembly during the crosslinking process. This finding is consistent with the structural characterization results of hydrogel pads based on MC and self-assembled SA matrices. Compared with MC-SA and MC-SA-Ant, hydrogels containing MOFs (Fe-MOFs, Ag-MOFs, ZIF-8) exhibit a denser porous structure. This is because MOFs enhance the crosslinking density of MC-SA-based hydrogels through physical crosslinking, and this tight shrinkage phenomenon significantly improves the mechanical properties and water retention capacity of the hydrogel pads.

[0048] The distribution of carbon (C), oxygen (O), nitrogen (N), zinc (Zn), silver (Ag), and iron (Fe) elements in each group of hydrogel pads was further examined to assess whether the incorporation of antifungal agents (Ant) and molecular sieves (MOFs) would induce elemental aggregation in the MC-SA-based hydrogels. The results showed that the addition of antifungal agents and the three different molecular sieves did not cause aggregation in the MC-SA-based hydrogels, indicating that the interactions between the molecular components in the entire hydrogel system had reached equilibrium. These findings further confirm that the encapsulation of antifungal agents by molecular sieves does not affect the structural homogeneity of the MC-SA-based hydrogels.

[0049] (II) Fourier Transform Infrared Spectroscopy (FTIR) Analysis The effects of antimicrobial peptide (Ant) and different metal-organic framework (MOF) loadings on functional group vibrations in hydrogel pads were observed using Fourier transform infrared spectroscopy (FTIR) (Nicolet IS5, Thermo Fisher, USA). Figure 5 As shown, after loading Ant and Fe-MOFs, the absorption peak of the polysaccharide structure is in the range of 950-1200 cm⁻¹. -1 The vibrational absorption peak showed a significant shift when Ant was encapsulated in MOFs and loaded onto a hydrogel pad. (3300-3400 cm⁻¹) -1 The range corresponds to the stretching vibrations of OH and NH, while 1650 cm⁻¹ -1 The absorption peak at 1400 cm⁻¹ is attributed to the aminoformamide I vibration (manifested as C=O stretching vibration and NH bending vibration), and the absorption peak at 1400 cm⁻¹. -1 The CH bending vibration absorption peaks at various locations all showed a trend consistent with the structural vibrations of the polysaccharide. Among these materials, the vibrational absorption peak shift of MC-SA-Ant@Fe-MOFs was the most significant. The results indicate that during the crosslinking process, the phenolic hydroxyl groups or other organic functional groups of Ant, Fe-MOFs, or Ant@MOFs interact with groups such as NH groups in the MC-SA matrix through hydrogen bonding or electrostatic interactions. Furthermore, as the loading or composition of Ant, Fe-MOFs, or Ant@MOFs changes, the stretching or bending vibrations of the corresponding functional groups become more pronounced. Notably, changes in the loading components did not alter the spectral characteristics of the hydrogel pad, further indicating that the incorporation of Ant and MOFs did not induce structural changes in the MC-SA polymer chain.

[0050] (III) X-ray diffraction (XRD) analysis The samples were analyzed using an X-ray powder diffractometer (D8 Advance, Bruker, Germany) under the following conditions: 40 kV and 40 mA, scanning from 5° to 60° in the 2θ region, at a scan rate of 0.02° / min. The results are as follows: Figure 6 As shown in the figure, when the MC-SA hydrogel pad is loaded with Ant, Fe-MOFs, and composite particles of Ant and various MOFs, characteristic peaks of varying intensities are observed at 31.7 nm and 45.8 nm. These peaks reflect changes in the average distance between crosslinking points or the microdomain size within the MC-SA hydrogel network. The incorporation of Ant and MOFs during the crosslinking process promotes the formation of superlattices or mesostructures, leading to a certain degree of ordered aggregation or assembly. This alters the characteristic parameters of particle spacing, domain size, and pore size in the hydrogel matrix.

[0051] III. Water Absorption Performance Test of Composite Hydrogel Pads The water absorption capacity, water retention capacity, and swelling properties of the hydrogel pad are the key performance indicators in this study. Water absorption capacity reflects the hydrogel pad's ability to absorb moisture exuded from the pork. Low water absorption rate, on the other hand, leads to moisture accumulation on the pork surface, accelerating spoilage.

[0052] The water absorption rate was measured by immersing a dried hydrogel pad in a beaker containing distilled water. The water absorption capacity was then determined based on the weight difference before and after water absorption. The water retention capacity was assessed by placing the fully expanded hydrogel pad at room temperature (24°C) for 40 hours, measuring the water content every 5 hours. The water absorption and retention capacities are as follows: Figure 7 and Figure 8 As shown.

[0053] from Figure 7 The results show that the water absorption rate of the MC-SA hydrogel pad alone is only 168.6%; after adding Ant or MOFs, the water absorption rate increases to 197.4%-260.3%. Notably, the water absorption rate of the hydrogel pads increased by more than 350% after loading with Ant and MOF composite particles. The MC-SA-Ant@Fe-MOFs hydrogel pad showed the most significant increase in water absorption rate, reaching 511.4%, the highest among all groups, demonstrating excellent water absorption capacity.

[0054] also, Figure 8The changes in water retention capacity of each hydrogel group after 40 hours at 4°C were shown. The water retention capacity of all hydrogel groups decreased to varying degrees within 40 hours, with the MC-SA and MC-SA-Ant hydrogels showing the most significant decreases. By 40 hours, their water retention rates had decreased to 29.7% and 35.3%, respectively. Hydrogel pads loaded with MOFs (especially those containing Ant-MOF composite particles) exhibited superior water retention performance. Notably, the MC-SA-Ant@Fe-MOFs hydrogel pad maintained a water retention rate of 88.9% after 40 hours.

[0055] At room temperature (24℃), each group of dried hydrogel pads was wrapped in gauze and placed in a container filled with distilled water. The swelling performance was then determined based on the difference in weight before and after swelling.

[0056] Figure 9 The swelling characteristics of each hydrogel pad group were demonstrated. Neither MC-SA nor MC-SA-Ant exhibited a swelling rate exceeding 200%. After loading with MOFs, their swelling performance was significantly improved, with MC-SA-Ant@Fe-MOFs showing a swelling rate as high as 723.3%. This result is consistent with the observed trends in water absorption and retention capacity.

[0057] Based on the three indicators mentioned above, the MC-SA-Ant@Fe-MOFS composite pad exhibits excellent water absorption, water retention, and swelling properties. In particular, compared to MC-SA-Ant, MC-SA@Fe-MOFs, MC-SA-Ant@ZIF-8, and MC-SA-Ant@Ag-MOFs, the porous structure synergistically constructed with Fe-MOFs and Ant further increases the network porosity of the hydrogel, promoting water absorption and locking, ensuring its rapid absorption of meat exudates, maintaining a dry environment inside the packaging, and physically inhibiting microbial growth.

[0058] IV. Three-phase contact angle test of composite hydrogel pads The water contact angle (WCA) of a hydrogel pad reflects its surface wettability, which affects its water affinity and potential functional applications. Hydrogel pads with a WCA < 90 are considered hydrophilic, while those with a WCA > 90 are hydrophobic.

[0059] The contact angle of the hydrogel pad samples was determined using an optical contact angle analyzer (OCA25, dataphysiSA, Germany). A 4 μL drop of deionized water was placed on the pad surface using the pendant drop method, and the contact angles on both sides of the drop were measured using the SCA20 program. The results are as follows: Figure 10As shown, the WCA of all hydrogel samples was less than 90, and the WCA of the entire hydrogel system gradually decreased with the increase of the loading of antibiotin (Ant), metal-organic frameworks (MOFs) and their composite particles. Among them, MC-SA-Ant@Fe-MOFs had the lowest WCA, only 34.25, which was significantly lower than other hydrogel samples.

[0060] V. Antibacterial properties, antioxidant activity and biocompatibility testing of composite hydrogel pads (a) Antibacterial test The antibacterial activity of the hydrogel pad against Staphylococcus aureus and Escherichia coli was evaluated using the inhibition zone diameter method. 200 μL of bacterial suspension (10... 5 The sterilized hydrogel sample (CFU / mL) was evenly spread onto an agar plate. A well was then punched in the center of the agar plate. The sterilized hydrogel sample was placed in the well and incubated at 37°C for 24 hours. Antimicrobial activity was assessed by measuring the diameter of the inhibition zone formed around the hydrogel sample.

[0061] The results are as follows Figure 11 As shown in the figure, the inhibition zone diameters of MC-SA against Staphylococcus aureus and Escherichia coli were 14.97±0.61 mm and 15.87±0.51 mm, respectively. Compared with MC-SA, hydrogels containing Ant and MOFs exhibited larger inhibition zones, with MC-SA-Ant@ZIF-8 (Staphylococcus aureus: 17.19±0.20 mm, Escherichia coli: 19.66±0.26 mm), MC-SA-Ant@Ag-MOFs (Staphylococcus aureus: 17.96±0.47 mm, Escherichia coli: 20.97±0.84 mm), and MC-SA-Ant@Fe-MOFs (Staphylococcus aureus: 18.55±0.69 mm, Escherichia coli: 20.11±0.51 mm) showing particularly significant inhibition zone diameters. Neither MC nor SA, when used alone, exhibits significant broad-spectrum direct antibacterial or bactericidal effects. However, when loaded with Ant@MOFs composite particles, the antibacterial ability of the hydrogel pad is significantly enhanced. This is primarily due to the inherent antibacterial properties of Ant and the ability of MOFs to release metal cations and superoxide radicals. These substances can disrupt cell membrane permeability and inhibit intracellular enzyme activity. The synergistic effect of these two components further enhances the antibacterial effect.

[0062] (ii) Antioxidant test The antioxidant activity of hydrogel membrane samples was evaluated using commercially available DPPH and ABTS free radical scavenging kits. 0.1 g of the hydrogel membrane sample was weighed and 1 mL of 80% methanol extract was added. The sample was then sonicated at 200-300 W for 30 min at 60°C. After sonication, the sample was centrifuged at 12000 rpm for 10 min at room temperature (24°C), and the supernatant was collected. The supernatant was mixed with DPPH or ABTS working solution, and the absorbance of the mixture at 517 nm (DPPH) and 734 nm (ABTS) was measured. The free radical scavenging rate was calculated using the formula provided in the kit. The results are shown below. Figure 12 and Figure 13 As shown.

[0063] As shown in the figure, the MC-SA hydrogel without any loaded components exhibited significantly weaker DPPH radical scavenging ability (0.125 μg Trolox / mL) and ABTS radical scavenging ability compared to hydrogels loaded with Ant or MOFs. This is related to the lack of strong antioxidant properties in the matrix itself. Among them, the Ant- and MOF-loaded composite hydrogels showed significantly higher free radical scavenging abilities. Particularly noteworthy is that MC-SA-Ant@ZIP-8 and MC-SA-Ant@Ag-MOFs showed similar DPPH and ABTS radical scavenging abilities to MC-SA-Ant. However, the hydrogel pad made of MC-SA-Ant@Fe-MOFs exhibited the strongest antioxidant activity, with a DPPH radical scavenging ability of 0.224 μg Trolox / mL and an ABTS radical scavenging ability of 290.450 μg Trolox / mL, demonstrating the best antioxidant performance among all hydrogel pads.

[0064] (iii) Biocompatibility testing The biocompatibility of the hydrogel pad was evaluated based on cell viability assays using Caco-2 cells and a CCK-8 assay kit. Sterile hydrogel samples (0.1 g / mL) were immersed in complete culture medium at 37°C for 24 hours, followed by filtration to obtain the hydrogel extract. The extract was then added to a mixture containing Caco-2 cells (cell density = 102). 5 Cells were placed in 96-well plates (cells / mL). The plates were incubated at 37°C under a 5% CO2 atmosphere for 24 hours, and cell viability was measured using a CCK-8 assay kit. Results are as follows: Figure 14 As shown.

[0065] As shown in the figure, the cell viability after 24 and 48 hours of incubation with MC-SA was 97.14±0.58% and 97.18±0.89%, respectively. In contrast, the cell viability after incubation with Fe-MOFs-loaded hydrogel pads decreased significantly to 75.05±0.39% and 75.63±0.89% at 24 and 48 hours, respectively. This is mainly because the metal cations in MOFs induce the production of reactive oxygen species (ROS) and other free radicals in mitochondria under cellular stress, ultimately leading to cell death. For the same reason, the cell viability induced by the MC-SA-Ant@ZIF-8 (84.23±1.89% / 83.64±0.64%), MC-SA-Ant@Ag-MOFs (85.23±1.07% / 84.51±1.62%), and MC-SA-Ant@Fe-MOFs (85.24±0.63% / 83.35±0.88%) groups, although lower than that of the MC-SA and MC-SA-Ant groups, was significantly higher than that of the Fe-MOFs-loaded hydrogels alone. This is attributed to the antioxidant and anti-inflammatory properties of polyphenols, which appear to mitigate the effects of metal cations on cells. According to the standard, since the cell viability did not fall below 70%, it was not considered cytotoxic. All groups showed values ​​exceeding 70% at 48 hours, indicating good biocompatibility of these composite hydrogel pads.

[0066] VI. pH-responsive color change and controlled release capabilities of composite hydrogel pads One of the most notable characteristics of protein-rich foods (such as meat and dairy products) during the breakdown process is a significant increase in pH levels, which can be used to monitor the freshness of meat.

[0067] (a) pH-responsive color change ability The hydrogel pads from each group were immersed in buffer solutions with different pH values ​​(from 5.0 to 7.5), and the color changes were observed. The color results of the hydrogels at different pH values ​​(from 5.0 to 7.5) are shown below. Figure 15 As shown, As shown in the figure, the hydrogel containing Ant underwent varying degrees of color change. When the environment changed from acidic to alkaline, the color of Ant changed from light gray to dark purple. The color gradient in the Ant-MOF composite hydrogel was more pronounced than in other composites. This may be attributed to the uniform and dense network structure of the composite, making Ant more sensitive to pH changes. Therefore, the synergistic effect between the hydroxyl groups at the ends of Ant and the MC-SA matrix became more significant, resulting in a more pronounced color change in Ant. Overall, the synergistic effect between Ant and MOFs enhanced the hydrogel's pH responsiveness. During pork preservation, a significant color change with pH value can be observed, allowing for a preliminary assessment of the meat's freshness by directly observing the color of the preservation pad, thus achieving the dual functions of active preservation and intelligent indication.

[0068] (ii) The ability of the composite hydrogel pad to release anthocyanins at different pH levels The hydrogel pads prepared in Examples 1, 1, 3, and 4 were used as test samples. Five grams of each sample were immersed in PBS buffer containing 15% ethanol at pH values ​​of 5.0, 6.0, 7.0, or 8.0. The samples were then shaken at 100 r / min in the dark at room temperature. Samples were removed at predetermined time points, and absorbance at 273 nm, 423 nm, and 515 nm was measured using a UV-Vis spectrophotometer. The cumulative release of anthocyanins (Ant) from the hydrogels was calculated using a standard curve. Results are as follows: Figure 16-19 As shown, Figure 16 Ant release curves for MC-SA-Ant hydrogel pads in the pH range of 5.5 to 7.0; Figure 17 Ant release curves for the MC-SA-Ant@ZIF-8 hydrogel pad in the pH range of 5.5 to 7.0; Figure 18 Ant release curves for MC-SA-Ant@Ag-MOFs hydrogel pads in the pH range of 5.5 to 7.0; Figure 19 Ant release curves for MC-SA-Ant@Fe-MOFs hydrogel pads in the pH range of 5.5 to 7.0.

[0069] As shown in the figure, under all pH conditions, the release rate of Ant increased rapidly in the first 12 hours, then tended to stabilize or slow down. This is likely due to the cross-linked spatial network pores formed by MC and SA restricting the release of Ant. Furthermore, compared to hydrogels without MOFs, the release rate of the Ant@MOF synergistic hydrogel was significantly reduced at the same pH level. This is attributed to the denser spatial structure and smaller pore size formed by the interaction of MOFs and MC-SA, which creates a more tortuous diffusion path for Ant, thus slowing down the release rate.

[0070] Furthermore, the release rate of Ant in each hydrogel was negatively correlated with pH. In MOF-free hydrogels, H₂ under acidic conditions… + Ions attack the glycosidic bonds of MC and SA, causing bond breakage and accelerating Ant release. In contrast, in MOF-containing hydrogels, MOFs rapidly dissociate under acidic conditions, triggering rapid Ant release, while maintaining high stability under neutral or alkaline conditions. This stability helps maintain the structural integrity of Ant, ensuring sustained release. Given that the pH of meat increases with prolonged storage, Ant@MOF hydrogels offer a significant advantage in maintaining freshness during extended storage of meat products.

[0071] VII. Test on the preservation effect of composite hydrogel mats on pork (a) Impact on the physicochemical properties (appearance) of pork during storage Using uniform and fresh pork tenderloin samples, pork samples of similar weight were divided into ten groups and placed on hydrogel mats. The blank control group was untreated, while the positive control group was sealed with wood fiber. The experimental groups used the following materials: pure MC-SA composite mats (control group), MC-SA mats containing antibiological agents (MC-SA-Ant), MC-SA mats loaded with Fe-MOFs (MC-SA@Fe-MOFs), and MC-SA mats loaded with Ant@ZIF-8, Ant@Ag-MOFs, or Ant@Fe-MOFs (MC-SA-Ant@ZIF-8, MC-SA-Ant@Ag-MOFs, MC-SA-Ant@Fe-MOFs).

[0072] Samples treated with different hydrogel pads were stored at 4°C, and their physicochemical parameters (correlation with freshness) were measured on days 0, 1, 3, 5, 7, and 9. The appearance changes of fresh pork during the 9-day storage period are shown below. Figure 20 As shown. From Figure 20 As can be seen, all pork samples showed varying degrees of discoloration and lipid separation as storage time increased.

[0073] To quantitatively assess these changes, we measured the color parameters of the refrigerated pork in each group during storage: L* (lightness / darkness), a* (redness / greenness), and b* (yellowness / blueness). Each sample was measured three times, and the average value was taken. The results are shown in Table 2 below.

[0074] Table 2 Color changes of pork during storage

[0075] The results indicate that the L* values ​​of all groups decreased with increasing storage time, suggesting that the pork samples gradually darkened. On day 9, the L* values ​​of samples coated with MC-SA-Ant@ZIF-8 and MC-SA-Ant@Ag-MOFs were not significantly different from those of the Wood fiber group, while only the L* value of samples coated with MC-SA-Ant@Fe-MOFs (46.27±0.35) was significantly higher than that of other groups. This suggests that MC-SA-Ant@Fe-MOFs can effectively delay the spoilage and discoloration of pork. Similarly, the a* and b* values ​​of the MC-SA-Ant@Fe-MOFs group decreased more slowly, indicating that it also reduces the loss of red and yellow color caused by oxidation.

[0076] (II) Impact on oxidation indicators during pork storage 1. Thiol and carbonyl content The total thiol and carbonyl content in meat protein are key indicators of protein oxidation. During storage, protein oxidation converts thiols into disulfide bonds, leading to a decrease in total thiol content. Simultaneously, free radicals generated during protein oxidation attack amino acid side chains, causing an increase in carbonyl content.

[0077] Commercially available kits were used to assess the degree of protein oxidation in pork samples from different treatment groups by detecting the total thiol and total carbonyl groups. The specific procedures were as follows: 0.1 g of pork tissue was weighed, and 1 mL of pre-chilled extraction buffer was added. The mixture was homogenized on ice. The homogenate was centrifuged at 10,000 rpm for 10 minutes at 4°C, and the supernatant was collected for subsequent analysis. After adding the colorimetric reagent according to the kit instructions, the absorbance was measured at 412 nm (total thiol) and 370 nm (total carbonyl) wavelengths using a spectrophotometer. Finally, the thiol and carbonyl groups were calculated using the formulas provided in the kit instructions.

[0078] The results are as follows: Figure 21 and 22 As shown, from Figure 21 As can be seen, the total thiol content of all groups gradually decreased with prolonged storage time. By day 9, the thiol content of MC-SA-Ant@Fe-MOFs (46.25 ± 0.65 μmol / g) was significantly higher than that of other groups. The thiol content of MC-SA-Ant@ZIF-8 (40.92 ± 0.15 μmol / g) and MC-SA-Ant@Ag-MOFs (39.35 ± 1.56 μmol / g) was not significantly different from that of MC-SA-Ant (38.65 ± 0.56 μmol / g).

[0079] from Figure 22As can be seen, the observed carbonyl content trend was opposite to that of thiol content, with all groups gradually increasing over time. On day 9, the carbonyl content of the MC-SA-Ant@Fe-MOFs (1.71±0.04 nmol / mg protein) group was significantly lower than that of the MC-SA-Ant@ZIF-8 (2.20±0.14 nmol / mg protein) group and the MC-SA-Ant@Ag-MOFs (2.25±0.08 nmol / mg protein) group, fully demonstrating its excellent antioxidant efficacy.

[0080] 2. Total volatile basic nitrogen (TVB-N) Changes in TVB-N (total free amine nitrogen) concentration can be used as an indicator of meat freshness.

[0081] Mix 20g of chopped pork tenderloin with 100ml of deionized water, stir for 30 minutes, and then filter. Take 5ml of the filtrate and alkalize it with 5ml of magnesium oxide solution (10g / L), followed by steam distillation using a Kjeldahl apparatus for 5 minutes. Place the collected distillate in a flask containing 10ml of boric acid solution (20g / L) and 2-3 drops of 0.1% methyl red-methylene blue, and finally titrate with 0.005 mol / L sulfuric acid standard solution.

[0082] The results are as follows Figure 23 As shown, the TVB-N content in all groups was negligible during the initial storage period. However, the TVB-N content gradually increased with prolonged storage. According to GB 2707-2016, the TVB-N content in fresh meat should not exceed 15 mg / 100g. By the fifth day of storage, the TVB-N content in the control group and the lignocellulosic group reached 18.28±0.39 mg / 100g and 16.87±0.42 mg / 100g, respectively, exceeding this limit, indicating the onset of spoilage. In contrast, by the ninth day of storage, only the MC-SA-Ant@Fe-MOFs group maintained a TVB-N content below the limit (13.26±0.45 mg / 100g), demonstrating the strongest preservation ability of this hydrogel pad.

[0083] 3. Thiobarbituric acid reactants (TBARS) TBARS content is another important indicator of lipid oxidation in meat. One gram of meat sample was homogenized with 15 mL of a mixed solution containing 7.5% thiobarbituric acid (TBA) and 0.1% ethylenediaminetetraacetic acid (EDTA) and filtered. One mL of the filtrate was mixed with 1.0 mL of a 20 mM TBA aqueous solution and heated in a boiling water bath for 20 minutes. After cooling, the absorbance at 532 nm was measured using a microplate reader (SpectraMaxiD3, Molecular Equipment Corporation, USA). A calibration curve was established using a 1,1,3,3-tetraethoxypropane (TEP) standard solution. TBARS values ​​are expressed as milligrams of malondialdehyde (MDA) per kilogram of meat sample (mg MDA / kg).

[0084] The results are as follows Figure 24 As shown in the figure, the trend of TBARS values ​​is similar to that of TVB-N. When lipid oxidation intensifies, ketone body accumulation reaches 1.0 mg MDA / kg, a level typically associated with spoilage and unpleasant odors. On day 9 of storage, the TBARS values ​​of the control group and the lignocellulosic group reached 1.32±0.02 and 1.16±0.03 mg MDA / kg, respectively, both exceeding this threshold, indicating significant lipid oxidation and spoilage. Meanwhile, the meat products in the hydrogel mat group containing the Ant and MOF composite particles showed significantly lower TBARS values ​​on day 9 of storage compared to other groups. Overall, these results indicate that the synergistic effect of Ant and MOFs can effectively delay the oxidation of proteins and lipids in meat, thereby extending shelf life and preventing the development of off-odors during storage.

[0085] Considering both physicochemical indicators (appearance) and oxidation indicators (thiol and carbonyl content, total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactants (TBARS)), pork tenderloin treated with MC-SA-Ant@Fe-MOFs hydrogel pads exhibited the best appearance and preservation effect. This invention significantly delays pork spoilage through a combination of physical water absorption, antibacterial and antioxidant properties, and intelligent controlled release.

[0086] 8. The effect of composite hydrogel mats on total viable bacterial count (TVC) during pork storage The spoilage of refrigerated fresh meat is mainly caused by the combined effects of oxidative protein degradation and microbial proliferation. Therefore, the TVC (Total Volatile Protein Content) value is a key indicator for assessing meat freshness and determining the timing of spoilage. Studies have shown that when the TVC value exceeds 6 log (CFU), the meat is considered spoiled and unsuitable for consumption.

[0087] Mix 25g of pork sample with 225ml of sterile physiological saline in a sterile beaker and homogenize for 2 minutes. Prepare 10-fold serial dilutions of the homogenate, and spread an appropriate amount of each dilution onto PCA (Polydioxanone) agar. Incubate the plates at 37°C for 48 hours, then count the colonies to determine the total viable count.

[0088] The results are as follows Figure 25 As shown in the figure, the TVC values ​​of the blank group (6.81±0.10 log(CFU)) and the lignocellulosic fiber group (6.22±0.07 log(CFU)) exceeded the threshold on the 7th day of storage. In contrast, only the MC-SA-Ant@Ag-MOFs (5.7 log(CFU)) and MC-SA-Ant@Fe-MOFs (5 log(CFU)) groups maintained TVC values ​​below 6 log(CFU) after 9 days of storage. Among them, the MC-SA-Ant@Fe-MOFs group showed a slower rate of increase, remaining around 5 log(CFU) after 9 days, indicating that MC-SA-Ant@Fe-MOFs can extend the spoilage period of pork and has a good preservation effect.

[0089] Based on all the measured indicators, this invention uses MC and SA as hydrogel matrices and successfully develops biodegradable smart composite hydrogel absorbent pads by loading Ant into ZIF-8, Ag-MOFs, and Fe-MOFs materials. These pads not only have antibacterial, antioxidant, water absorption, and water storage properties, but also achieve pH-responsive color change and controllable Ant release. In pork preservation applications, MC-SA-based hydrogel pads containing antimicrobial peptides (Ant) and metal-organic frameworks (MOFs) can monitor pork freshness in real time. Among all formulations, the MC-SA-Ant@Fe-MOFs group exhibits the best overall performance, extending the shelf life of meat by 2-4 days.

[0090] Although the present invention has been described using the above preferred embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by those skilled in the art to the above embodiments without departing from the spirit and scope of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A multifunctional absorbent composite food preservation mat, characterized in that, Using methylcellulose-sodium alginate (MC-SA) as a composite hydrogel matrix, an anthocyanin-loaded iron-based metal-organic framework material Ant@Fe-MOFs was uniformly dispersed in the composite hydrogel matrix to obtain a multifunctional absorbent composite food preservation pad MC-SA-Ant@Fe-MOFs.

2. The preparation method of the multifunctional absorbent composite food preservation pad according to claim 1, characterized in that, Includes the following steps: (1) Preparation of composite hydrogel matrix Sodium alginate powder (SA) was dissolved in a deionized solution to prepare a sodium alginate dispersion. Methylcellulose (MC) was dispersed in preheated deionized water and heated and stirred until completely dissolved to prepare a methylcellulose dispersion. The sodium alginate dispersion and the methylcellulose dispersion were mixed and stirred evenly to obtain a mixed solution. A crosslinking agent was added to the mixed solution and stirred evenly to obtain a composite hydrogel matrix MC-SA with a preliminary gel network. (2) Preparation of anthocyanin-loaded iron-based metal-organic framework composites 2,5-Dihydroxyterephthalic acid and 2-aminoterephthalic acid were dissolved in methanol to prepare a first solution. Imidazole organic ligands were dissolved in methanol, and anthocyanin Ant was added and stirred until completely dissolved to prepare a second solution. Iron salts were dissolved to obtain a third solution. The first, second, and third solutions were mixed, stirred evenly, centrifuged, and the precipitate was collected. After washing and drying, anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs was obtained. (3) Preparation of composite hydrogel absorbent pad The anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs was added to the composite hydrogel matrix MC-SA and ultrasonically mixed to obtain a film-forming solution. After film formation and drying, the composite hydrogel absorbent pad MC-SA-Ant@Fe-MOFs was obtained.

3. The method for preparing the multifunctional absorbent composite food preservation mat according to claim 2, characterized in that, In step (1), the concentration of sodium alginate dispersion is 2-4% w / v; the concentration of methylcellulose dispersion is 1-3% w / v.

4. The preparation method of the multifunctional absorbent composite food preservation pad according to claim 2, characterized in that, In step (2), the mass ratio of 2,5-dihydroxyterephthalic acid to 2-aminoterephthalic acid is 1:

1.

5. The method for preparing the multifunctional absorbent composite food preservation pad according to claim 2, characterized in that, In step (2), the imidazole organic ligand is 2-methylimidazole, and the mass ratio of the iron salt, 2-methylimidazole and anthocyanin is (7-12):(5-10):(3-7).

6. The method for preparing the multifunctional absorbent composite food preservation mat according to claim 2, characterized in that, In step (3), the anthocyanin-loaded iron-based metal-organic framework composite material Ant@Fe-MOFs accounts for 1 to 5% of the total solid mass of the composite hydrogel matrix MC-SA.

7. The method for preparing the multifunctional absorbent composite food preservation pad according to claim 2, characterized in that, In step (1), the crosslinking agent is an anhydrous calcium chloride solution or citric acid solution with a mass fraction of 1-5%.

8. The method for preparing the multifunctional absorbent composite food preservation pad according to claim 2, characterized in that, In step (3), the power of ultrasonic treatment is 100-150W and the time is 30-45min.

9. The method for preparing the multifunctional absorbent composite food preservation pad according to claim 2, characterized in that, In step (3), the film-forming process involves casting the film-forming solution onto a mold and drying it at a temperature of 40-50°C for 36-48 hours.

10. The application of the multifunctional absorbent composite preservation mat according to claim 1 in the preservation of chilled meat.

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