EEO@ZIF-8 / CG composite film, preparation method thereof, and fresh-keeping liner based on the film and application thereof

Abstract

This invention provides an EEO@ZIF-8 / CG composite film, its preparation method, and a preservation liner based on a preservation film, belonging to the field of preservation materials technology. The preparation method of this invention includes the following steps: adding a zinc salt aqueous solution to a 2-methylimidazole aqueous solution, sequentially allowing it to stand, centrifuging, and drying to obtain ZIF-8 particles; ultrasonically mixing the ZIF-8 particles and eucalyptus oil, then sequentially centrifuging and drying to obtain EEO@ZIF-8 particles; mixing gelatin solution, chitosan solution, glycerol, and EEO@ZIF-8 particles, then sequentially stirring, ultrasonicating, and drying to obtain the EEO@ZIF-8 / CG composite film. The EEO@ZIF-CG liner of this invention results in fish fillets with the lowest rate of increase in TVC, TVB-N, pH value, and TBA, effectively maintaining the muscle tissue structure of the fish fillets and delaying the deterioration of their appearance and color.

Description

Technical Field

[0001] This invention relates to the field of preservation materials technology, and in particular to an EEO@ZIF-8 / CG composite film, its preparation method, and a preservation liner based on the preservation film and its application. Background Technology

[0002] Plant essential oils are an important class of plant secondary metabolites with significant broad-spectrum antibacterial properties and good biocompatibility, making them promising natural preservatives for the food industry. Eucalyptus oil (EEO), primarily derived from the eucalyptus tree (Eucalyptus stenoptera), possesses certain antibacterial and antioxidant properties. However, its high volatility makes direct application in food preservation difficult. Encapsulating it in a slow-release system can significantly enhance its preservation effect.

[0003] Metal-organic frameworks (MOFs) are among the most compelling types of porous materials of the last decade. ZIF-8 is a MOF with a high specific surface area and high porosity, composed of Zn... 2+ Composed of a 2-methylimidazole group, it possesses excellent biocompatibility and physicochemical stability, and exhibits certain antibacterial properties; it demonstrates good antibacterial activity against foodborne Staphylococcus aureus and Escherichia coli. ZIF-8 holds promise for adsorbing eucalyptus oil to form a sustained-release structure.

[0004] The development of food packaging using natural bioactive compounds and biopolymers is receiving increasing attention. Chitosan (CS) is a linear biopolymer extracted from crustacean shells. During antibacterial processes, it interacts with the negatively charged cell membranes of microorganisms through the positive charge of its amino groups, leading to membrane rupture. It exhibits excellent antibacterial properties, biocompatibility, biodegradability, and film-forming properties. Gelatin (GA) is a biopolymer made by denaturing and hydrolyzing collagen. It possesses excellent gelling and thickening properties, making it widely used in the food industry. Due to its excellent gas barrier properties, biocompatibility, biodegradability, and mechanical properties, gel-based films are commonly used in food packaging.

[0005] Sea bass, a high-value aquaculture species in East Asia, has an annual production exceeding 150,000 tons. However, due to its delicate muscle tissue and high water content (>80%), it is susceptible to microbial contamination and fat oxidation during refrigeration, resulting in a significantly shortened shelf life (only 6-8 days at 4°C) and causing substantial economic losses. While traditional polyethylene (PE) packaging can physically block microbial contamination, it cannot inhibit enzymatic reactions and juice loss within the fish fillets, causing a 35-50% decrease in fish firmness and exceeding the K-value limit by 60% in the later stages of storage. Furthermore, its non-degradable nature exacerbates "white pollution" (plastic waste). In addition, commercially available preservation liners for aquatic products and meats are primarily made of absorbent resin, which absorbs the exudate from sea bass during storage, reducing humidity around the fish and inhibiting the growth of spoilage bacteria to some extent. However, this product suffers from poor water absorption dynamics, failing to quickly absorb the exudate, resulting in questionable preservation performance. Therefore, developing efficient and safe novel active packaging materials to extend shelf life by inhibiting the growth of dominant spoilage bacteria and protein and lipid oxidation in aquatic products has become a research hotspot in the field of aquatic product preservation. In recent years, biodegradable active films have become a research hotspot due to their combination of environmental friendliness and functional enhancement. Among them, chitosan-gelatin (CG) composite substrates form a dense network through hydrogen bonding and electrostatic interactions, while ZIF-8 can further enhance the mechanical strength of the film due to its small particle size. At the same time, both can serve as good carriers for biopreservatives and can construct a gradually released biopreservative system. The introduction of functional additives (such as EEO) can promote improved preservation performance through their antibacterial and antioxidant properties.

[0006] Therefore, it is of great significance to provide a composite film and preservation liner with chitosan-gelatin as the base material and ZIF-8 particles and eucalyptus oil added. Summary of the Invention

[0007] The purpose of this invention is to provide an EEO@ZIF-8 / CG composite film and its preparation method, as well as a food preservation liner based on food preservation film and its application, in order to address the shortcomings of the prior art.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing an EEO@ZIF-8 / CG composite membrane, comprising the following steps: 1) Add zinc salt aqueous solution to 2-methylimidazole aqueous solution, and sequentially allow to stand, centrifuge and dry to obtain ZIF-8 particles; 2) After ultrasonically mixing ZIF-8 granules and eucalyptus oil, the mixture was centrifuged and dried sequentially to obtain EEO@ZIF-8 granules; 3) After mixing the gelatin solution, chitosan solution, glycerol and EEO@ZIF-8 particles, the mixture is stirred, sonicated and dried in sequence to obtain the EEO@ZIF-8 / CG composite membrane.

[0009] Preferably, the zinc salt aqueous solution in step 1) is a zinc acetate aqueous solution or a zinc sulfate aqueous solution, the concentration of the zinc salt aqueous solution is 9~23 g / L, and the volume ratio of the zinc salt aqueous solution to the 2-methylimidazole aqueous solution is 8~12:16~24; when the zinc salt aqueous solution is a zinc acetate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is 135~155 g / L; when the zinc salt aqueous solution is a zinc sulfate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is 175~185 g / L.

[0010] Preferably, in step 1), the settling time is 22-26 hours, the centrifugation speed is 6000-8000 rpm, and the centrifugation time is 3-7 minutes; the drying temperature is 55-65℃, and the drying time is 22-26 hours; after centrifugation, the white precipitate is collected, washed with water, and then dried, and the washing is performed 2-4 times.

[0011] Preferably, in step 2), the mass ratio of ZIF-8 particles to eucalyptus oil is 1:1.8~2.2; the ultrasonic mixing frequency is 45~55kHz, and the ultrasonic mixing time is 25~35min; the centrifugation speed is 6000~8000rpm, and the centrifugation time is 3~7min; the drying temperature is 45~55℃, and the drying time is 1.5~2.5h; after centrifugation, the product is washed before drying, and the washing reagent is anhydrous ethanol, and the number of washings is 2~4 times.

[0012] Preferably, in step 3), the volume ratio of the gelatin solution to the chitosan solution is 2.5~3.5:1.5~2.5, the mass of glycerol is 18~22% of the total mass of gelatin and chitosan, and the mass of EEO@ZIF-8 particles is 4~6% of the total mass of gelatin and chitosan. The gelatin solution has a mass concentration of 45-55 g / L and is in water as the solvent; the chitosan solution has a mass concentration of 17-23 g / L and is in acetic acid solution with a mass fraction of 0.8-1.2%.

[0013] Preferably, the stirring time in step 3) is 22-26 hours, the drying temperature is 20-30°C, and the drying time is 45-52 hours.

[0014] The present invention also provides an EEO@ZIF-8 / CG composite membrane prepared by the aforementioned preparation method.

[0015] The present invention also provides an EEO@ZIF-CG composite film preservation liner comprising the aforementioned EEO@ZIF-8 / CG composite film, wherein the EEO@ZIF-CG composite film preservation liner comprises, from bottom to top, an absorbent bottom layer, an EEO@ZIF-8 / CG composite film, and a superhydrophobic mesh film.

[0016] Preferably, the absorbent bottom layer consists of non-woven fabric, absorbent cotton, bentonite, and non-woven fabric in that order from bottom to top.

[0017] The present invention also provides the application of the aforementioned EEO@ZIF-CG composite film preservation liner in the preservation of sea bass.

[0018] The beneficial effects of this invention are: This invention uses EEO as a preservative, ZIF-8 as a primary sustained-release system, and GA and CS as secondary sustained-release systems to prepare an EEO@ZIF-8 / CG composite membrane with long-lasting sustained-release properties. This membrane is then combined with non-woven fabric, absorbent cotton, and bentonite to prepare an absorbent and preservative liner, which is applied to the preservation of sea bass fillets. The fish fillets treated with the EEO@ZIF-CG liner show the lowest rate of increase in TVC, TVB-N, pH, and TBA, effectively preserving the muscle tissue structure and delaying the deterioration of the fillets' appearance and color. This invention provides theoretical guidance and technical support for the development of new technologies for preserving sea bass fillets. Attached Figure Description

[0019] Figure 1 The effect of the liner used in Example 1 and Comparative Examples 1-4 on the sensory scores of sea bass fillets during storage; Figure 2 The effect of the liners used in Example 1 and Comparative Examples 1-4 on the total bacterial count of sea bass fillets during storage; Figure 3 The effect of the liner used in Example 1 and Comparative Examples 1-4 on the TBA value of sea bass fillets during storage; Figure 4 The effect of the liners of Example 1 and Comparative Examples 1-4 on the pH value of sea bass fillets during storage; Figure 5 The effect of the liner used in Example 1 and Comparative Examples 1-4 on the TVB-N value of sea bass fillets during storage; Figure 6 The effect of the liner of Example 1 and Comparative Examples 1-4 on the textural properties of sea bass fillets during storage; Figure 7 The effect of the liner used in Example 1 and Comparative Examples 1-4 on the color difference of sea bass fillets during storage was investigated. L Represents brightness, a Representing red and green b Representing yellow and blue; Figure 8The images show the effect of the liners in Example 1 and Comparative Examples 1-4 on the appearance of sea bass fillets during storage. In this example, A is the untreated group, B is the blank liner, C is the CG liner, D is the EEO-CG liner, E is the ZIF-CG liner, and F is the EEO@ZIF-CG liner. Figure 9 The effect of the padding used in Example 1 and Comparative Examples 1-4 on the water-holding capacity of sea bass fillets during storage; Figure 10 The effects of the liners in Example 1 and Comparative Examples 1-4 on the muscle tissue structure of sea bass fillets during storage are shown in the figures. A is the untreated group, B is the blank liner, C is the CG liner, D is the EEO-CG liner, E is the ZIF-CG liner, and F is the EEO@ZIF-CG liner. Detailed Implementation

[0020] This invention provides a method for preparing an EEO@ZIF-8 / CG composite membrane, comprising the following steps: 1) Add zinc salt aqueous solution to 2-methylimidazole aqueous solution, and sequentially allow to stand, centrifuge and dry to obtain ZIF-8 particles; 2) After ultrasonically mixing ZIF-8 particles and eucalyptus oil (EEO), the mixture was centrifuged and dried sequentially to obtain EEO@ZIF-8 particles; 3) After mixing gelatin (GA) solution, chitosan (CS) solution, glycerol and EEO@ZIF-8 particles, the mixture is stirred, sonicated and dried in sequence to obtain EEO@ZIF-8 / CG composite membrane.

[0021] In this invention, the zinc salt aqueous solution in step 1) is a zinc acetate aqueous solution or a zinc sulfate aqueous solution. The concentration of the zinc salt aqueous solution is preferably 9~23 g / L, more preferably 12~18 g / L, and even more preferably 14~15 g / L. The volume ratio of the zinc salt aqueous solution to the 2-methylimidazole aqueous solution is preferably 8~12:16~24, more preferably 9~11:18~22, and even more preferably 10:20. When the zinc salt aqueous solution is a zinc acetate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is preferably 135~155 g / L, more preferably 140~150 g / L, and even more preferably 144~145 g / L. When the zinc salt aqueous solution is a zinc sulfate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is preferably 175~185 g / L, more preferably 178~182 g / L, and even more preferably 180 g / L.

[0022] In this invention, the settling time in step 1) is preferably 22-26 hours, more preferably 23-25 ​​hours, and even more preferably 24 hours; settling is preferably performed at room temperature; the centrifugation speed is preferably 6000-8000 rpm, more preferably 6500-7500 rpm, and even more preferably 7000 rpm; the centrifugation time is preferably 3-7 minutes, more preferably 4-6 minutes, and even more preferably 5 minutes; the drying temperature is preferably 55-65°C, more preferably 57-63°C, and even more preferably 60°C; the drying time is preferably 22-26 hours, more preferably 23-25 ​​hours, and even more preferably 24 hours; after centrifugation, the white precipitate is collected, washed with water, and then dried; the number of washings is preferably 2-4 times, and even more preferably 3 times.

[0023] In this invention, the mass ratio of ZIF-8 particles to eucalyptus oil in step 2) is preferably 1:1.8~2.2, more preferably 1:1.9~2.1, and even more preferably 1:2; the frequency of ultrasonic mixing is preferably 45~55kHz, more preferably 47~53kHz, and even more preferably 50kHz; the ultrasonic mixing time is preferably 25~35min, more preferably 27~33min, and even more preferably 30min; the centrifugation speed is preferably 6000~8000rpm, more preferably 6500~7500rpm, and even more preferably 7000rpm; the centrifugation time is preferably 3~7min, more preferably 4~6min, and even more preferably 5min; the drying temperature is preferably 45~55℃, more preferably 47~53℃, and even more preferably 50℃; the drying time is preferably 1.5~2.5h, and even more preferably 2h; after centrifugation, the product is washed before drying, the washing reagent is preferably anhydrous ethanol, and the number of washings is preferably 2~4 times, and even more preferably 3 times.

[0024] In this invention, step 2) involves ultrasonic mixing to fully embed eucalyptus essential oil in ZIF-8, followed by washing with anhydrous ethanol to remove excess essential oil from the surface of the ZIF-8 particles.

[0025] In this invention, the volume ratio of the gelatin solution and chitosan solution in step 3) is preferably 2.5~3.5:1.5~2.5, more preferably 2.8~3.2:1.8~2.2, and even more preferably 3:2. The mass of glycerol is preferably 18~22% of the total mass of gelatin and chitosan, more preferably 19~21%, and even more preferably 20%. The mass of EEO@ZIF-8 particles is preferably 4~6% of the total mass of gelatin and chitosan, more preferably 4.5~5.5%, and even more preferably 5%. The preferred mass concentration of the gelatin solution is 45-55 g / L, more preferably 47-53 g / L, and even more preferably 50 g / L, with water as the preferred solvent; the preferred mass concentration of the chitosan solution is 17-23 g / L, more preferably 18-22 g / L, and even more preferably 20 g / L, with acetic acid solution as the preferred solvent, and the preferred mass fraction of the acetic acid solution is 0.8-1.2%, more preferably 0.9-1.1%, and even more preferably 1%.

[0026] In this invention, the gelatin solution is preferably gelatin added to water and heated and stirred in a water bath at 50°C for 30 minutes; the chitosan solution is preferably chitosan added to acetic acid solution and heated and stirred in a water bath at 60°C for 30 minutes.

[0027] In this invention, the stirring time in step 3) is preferably 22-26h, more preferably 23-25h, and even more preferably 24h; the drying temperature is preferably 20-30℃, more preferably 22-28℃, and even more preferably 25-26℃; and the drying time is preferably 45-52h, more preferably 47-50h, and even more preferably 48-49h.

[0028] In this invention, the mixing is preferably a mixture of gelatin solution, chitosan solution and glycerin, and then mixed with EEO@ZIF-8 particles; the gelatin solution, chitosan solution and glycerin are mixed under water bath heating, and the mixing time is preferably 17~23 min, more preferably 20 min.

[0029] In this invention, stirring is carried out at room temperature, and ultrasonication is used to remove air bubbles from the membrane liquid.

[0030] The present invention also provides an EEO@ZIF-8 / CG composite membrane prepared by the aforementioned preparation method.

[0031] The present invention also provides an EEO@ZIF-CG composite film preservation liner comprising the aforementioned EEO@ZIF-8 / CG composite film, wherein the EEO@ZIF-CG composite film preservation liner comprises, from bottom to top, an absorbent bottom layer, an EEO@ZIF-8 / CG composite film, and a superhydrophobic mesh film.

[0032] In this invention, the absorbent bottom layer consists of non-woven fabric, absorbent cotton, bentonite, and non-woven fabric in that order from bottom to top.

[0033] The present invention also provides the application of the aforementioned EEO@ZIF-CG composite film preservation liner in the preservation of sea bass.

[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] In the examples and comparative examples, bentonite was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., the conductivity of deionized water was <15μS / cm, eucalyptus oil was purchased from Ji'an Huashuo Fragrance Oil Co., Ltd., gelatin was food grade and purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and chitosan was food grade and purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; the dry matter mass is the total mass of gelatin and chitosan.

[0036] Example 1

[0037] Dissolve 0.11 g of zinc acetate in 10 mL of water to obtain an aqueous solution of zinc acetate; dissolve 2.88 g of 2-methylimidazole in 20 mL of water to obtain an aqueous solution of 2-methylimidazole; quickly pour the aqueous solution of zinc acetate into the aqueous solution of 2-methylimidazole, let it stand at room temperature for 24 h, centrifuge at 7000 rpm for 5 min, collect the white precipitate, wash it 3 times with deionized water, and then dry it at 60 °C for 24 h to obtain ZIF-8 particles.

[0038] ZIF-8 particles were placed in eucalyptus oil (ZIF-8 particles to eucalyptus oil mass ratio of 1:2) and ultrasonically mixed at 50 kHz for 30 min to ensure thorough encapsulation of the eucalyptus oil. The particles were then centrifuged at 7000 rpm for 5 min and rapidly washed three times with anhydrous ethanol to remove excess oil from the surface of the ZIF-8 particles. Finally, they were dried at 50 °C for 2 h to obtain EEO@ZIF-8 particles encapsulated with EEO.

[0039] 5g of gelatin was placed in 100mL of deionized water and heated and stirred in a water bath at 50℃ for 30min to obtain a gelatin solution. 2g of chitosan was placed in 100mL of 1% acetic acid solution and heated and stirred in a water bath at 60℃ for 30min to obtain a chitosan solution. The gelatin solution and chitosan solution were mixed at a volume ratio of 3:2, and 20% (by dry matter) of glycerol was added. The mixture was heated and stirred in a water bath for 20min. 5% (by dry matter) of EEO@ZIF-8 particles were added to the coating solution, and the mixture was stirred at room temperature for 24h. After removing air bubbles from the coating solution by ultrasonication at 50kHz, the mixture was dried at 25℃ for 48h to obtain an EEO@ZIF-8 / CG composite membrane.

[0040] Spread 0.85g of absorbent cotton evenly on a 20cm×25cm non-woven fabric, then sprinkle 0.45g of bentonite evenly on the absorbent cotton, and then spread another layer of non-woven fabric on top of the bentonite. Press the two layers of non-woven fabric together with food-grade adhesive to obtain the absorbent bottom layer.

[0041] An EEO@ZIF-8 / CG composite membrane with a thickness of 200μm was placed on the absorbent bottom layer as the core layer, and a commercially available superhydrophobic membrane (2mm thick, 3mm pores) was placed on top of the composite membrane. The membrane was then sterilized under ultraviolet light for 30 minutes to obtain the EEO@ZIF-CG pad.

[0042] Example 2

[0043] Dissolve 0.15 g of zinc acetate in 10 mL of water to obtain an aqueous solution of zinc acetate; dissolve 3 g of 2-methylimidazole in 20 mL of water to obtain an aqueous solution of 2-methylimidazole; quickly pour the aqueous solution of zinc acetate into the aqueous solution of 2-methylimidazole, let it stand at room temperature for 25 h, centrifuge at 7500 rpm for 4 min, collect the white precipitate, wash it 3 times with deionized water, and then dry it at 65 °C for 22 h to obtain ZIF-8 particles.

[0044] ZIF-8 particles were placed in eucalyptus oil (ZIF-8 particles to eucalyptus oil mass ratio of 1:1.9) and ultrasonically mixed at 53 kHz for 30 min to ensure thorough encapsulation of the eucalyptus oil. The particles were then centrifuged at 7500 rpm for 4 min and rapidly washed three times with anhydrous ethanol to remove excess oil from the surface of the ZIF-8 particles. Finally, they were dried at 53℃ for 2 h to obtain EEO@ZIF-8 particles encapsulated with EEO.

[0045] 5.2 g of gelatin was placed in 100 mL of deionized water and heated and stirred in a water bath at 50 °C for 30 min to obtain a gelatin solution. 2.2 g of chitosan was placed in 100 mL of 1% acetic acid solution and heated and stirred in a water bath at 60 °C for 30 min to obtain a chitosan solution. The gelatin solution and chitosan solution were mixed at a volume ratio of 3.5:2.5, and 18% (by dry matter weight) of glycerol was added. The mixture was heated and stirred in a water bath for 20 min. 5.5% (by dry matter weight) of EEO@ZIF-8 particles were added to the coating solution, and the mixture was stirred at room temperature for 24 h. After removing air bubbles from the coating solution by ultrasonication at 50 kHz, the mixture was dried at 25 °C for 48 h to obtain an EEO@ZIF-8 / CG composite membrane.

[0046] Spread 0.85g of absorbent cotton evenly on a 20cm×25cm non-woven fabric, then sprinkle 0.45g of bentonite evenly on the absorbent cotton, and then spread another layer of non-woven fabric on top of the bentonite. Press the two layers of non-woven fabric together with food-grade adhesive to obtain the absorbent bottom layer.

[0047] An EEO@ZIF-8 / CG composite membrane with a thickness of 200μm was placed on the absorbent bottom layer as the core layer, and a commercially available superhydrophobic membrane (2mm thick, 3mm pores) was placed on top of the composite membrane. The membrane was then sterilized under ultraviolet light for 30 minutes to obtain the EEO@ZIF-CG pad.

[0048] Comparative Example 1

[0049] The EEO@ZIF-8 / CG composite membrane in Example 1 is omitted, and a superhydrophobic membrane is placed on the absorbent bottom layer to obtain a blank pad.

[0050] Comparative Example 2

[0051] 5g of gelatin was placed in 100mL of deionized water and heated and stirred in a water bath at 50℃ for 30min to obtain a gelatin solution. 2g of chitosan was placed in 100mL of 1% acetic acid solution and heated and stirred in a water bath at 60℃ for 30min to obtain a chitosan solution. The gelatin solution and chitosan solution were mixed at a volume ratio of 3:2, and 20% (by dry matter) of glycerol was added. The mixture was heated and stirred in a water bath for 20min, and after removing air bubbles by ultrasonication at 50kHz, it was dried at 25℃ for 48h to obtain a gelatin / chitosan composite membrane.

[0052] The core layer EEO@ZIF-8 / CG composite membrane in Example 1 was replaced with a gelatin / chitosan composite membrane, and other process conditions were the same as in Example 1, to obtain the CG liner.

[0053] Comparative Example 3

[0054] 5g of gelatin was placed in 100mL of deionized water and heated and stirred in a water bath at 50℃ for 30min to obtain a gelatin solution. 2g of chitosan was placed in 100mL of 1% acetic acid solution and heated and stirred in a water bath at 60℃ for 30min to obtain a chitosan solution. The gelatin solution and chitosan solution were mixed at a volume ratio of 3:2, and 20% (by dry matter) of glycerol was added. The mixture was heated and stirred in a water bath for 20min. 5% (by dry matter) of eucalyptus oil (EEO) was added to the coating solution, and the mixture was stirred at room temperature for 24h. After removing air bubbles from the coating solution by ultrasonication at 50kHz, the mixture was dried at 25℃ for 48h to obtain an EEO / CG composite membrane.

[0055] The core layer EEO@ZIF-8 / CG composite membrane in Example 1 was replaced with an EEO / CG composite membrane, and other process conditions were the same as in Example 1, to obtain an EEO-CG gasket.

[0056] Comparative Example 4

[0057] 5g of gelatin was placed in 100mL of deionized water and heated and stirred in a water bath at 50℃ for 30min to obtain a gelatin solution. 2g of chitosan was placed in 100mL of 1% acetic acid solution and heated and stirred in a water bath at 60℃ for 30min to obtain a chitosan solution. The gelatin solution and chitosan solution were mixed at a volume ratio of 3:2, and 20% (by dry matter) of glycerol was added. The mixture was heated and stirred in a water bath for 20min. 5% (by dry matter) of ZIF-8 particles were added to the coating solution, and the mixture was stirred at room temperature for 24h. After removing air bubbles from the coating solution by ultrasonication at 50kHz, the mixture was dried at 25℃ for 48h to obtain a ZIF / CG composite membrane.

[0058] The core layer EEO@ZIF-8 / CG composite membrane in Example 1 was replaced with an EEO / CG composite membrane, and other process conditions were the same as in Example 1, to obtain a ZIF-CG gasket.

[0059] The preservation performance of sea bass (purchased from Jinzhou Fresh Food Market) was tested on the liners of Example 1 and Comparative Examples 1-4. Fresh sea bass were slaughtered and skinned by market professionals, and the back meat from both sides was removed, with excess fat trimmed. Each piece of fish meat weighed 1305.00g. The fish meat was gently rinsed with sterile ultrapure water and then gently wiped dry with sterile paper. The untreated group was placed in an empty plastic storage container, while the remaining fish pieces were placed on the blank liner of Comparative Example 1, the CG liner of Comparative Example 2, the EEO-CG liner of Comparative Example 3, the ZIF-CG liner of Comparative Example 4, and the EEO@ZIF-CG liner of Example 1, respectively. All samples were stored at 4℃, and samples were collected for analysis at 0d, 3d, 6d, 9d, 12d, and 15d. All experimental results were measured three times and are expressed as mean ± standard deviation. Significance analysis (ANOVA-LSD, Duncan's algorithm) was performed using SPSS 27.0, and plotted using Origin 2024. p < 0.05 was considered statistically significant.

[0060] (1) Effect of padding on sensory rating of sea bass fillets: Following the UCAR method with slight modifications, 10 aquaculture students were randomly selected to form an evaluation group to conduct sensory evaluation of the fish meat in terms of color, smell and texture. 10 points is the best and 3 points is the minimum acceptable value.

[0061] The effects of the liners in Example 1 and Comparative Examples 1-4 on the sensory scores of sea bass fillets during storage are as follows: Figure 1 As shown. By Figure 1It was found that the sensory scores of all groups of fish fillets generally decreased with prolonged storage time. The untreated group showed the fastest decline in sensory scores, falling below the acceptable minimum threshold around day 11. After treatment with blank liners, the rate of decline slowed. This is because the juices seeping out during spoilage were absorbed by the absorbent layer of the liners, inhibiting bacterial growth and thus delaying spoilage. The decline in sensory scores was slower after CG liner treatment compared to the blank liner. This is because the dense network structure of the CG film regulates water migration within the liner, reducing free water accumulation and juice diffusion on the fish fillet surface, while CS exerts its weak antibacterial effect. Compared to CG liners, the decline in sensory scores was further slowed after EEO-CG liner treatment. This is because the EEO added to the EEO-CG liner has some antibacterial and antioxidant effects, but due to the lack of a secondary slow-release system, the essential oils were released rapidly in the early stages, leading to a rapid decline in the sensory scores. The rate of decline in sensory scores for fish fillets treated with ZIF-CG liners slowed further because ZIF-8 releases Zn during the shelf life. 2+ Zn 2+ By disrupting the cell membranes of spoilage bacteria, the spoilage of fish fillets was delayed. The sensory scores of fish fillets treated with EEO@ZIF-CG liners decreased most slowly, not reaching the minimum limit even after 15 days. This indicates that the two-stage slow-release system constructed with ZIF-8 and CG membranes enables the slow release of EEO during the preservation period, thereby effectively inhibiting microbial growth and delaying spoilage of the fish fillets.

[0062] (2) Effect of liner on total bacterial count of sea bass fillets: 10.00g of fish fillet was weighed into a sterile cooking bag, 90mL of sterile physiological saline was added, and the fillet was homogenized with a beater (manufacturer: Shanghai Zhili Scientific Instruments Co., Ltd., model: Bagmixer 400W) and allowed to stand. The supernatant was then collected and serially diluted. The solution was processed and calculated according to the method in GB4789.2-2022.

[0063] The effects of the liners in Examples 1 and 1-4 on the total bacterial count of sea bass fillets during storage are as follows: Figure 2As shown, the initial total viable count (TVC) of fresh fish fillets was 3.42 lg CFU / g. With prolonged storage, the TVC value of the fish fillets increased, with the untreated group showing the fastest increase, reaching the acceptable limit (7 lg CFU / g) at 4.5 days. The increase rate slowed after treatment with the blank liner, reaching the acceptable limit at 6.1 days. This indicates that the absorbent liner alone can absorb exudate from the fish fillets to some extent, reducing surface humidity and thus mitigating the spoilage effect of microbial growth; however, due to the lack of antibacterial activity, the TVC still increased rapidly. The TVC growth of fish fillets treated with CG liner slowed further. This is because the CG film (chitosan-gelatin film) has a relatively dense structure, and CS (chitosan) has certain antibacterial properties, which can reduce exudate residue on the fish surface to some extent and inhibit bacterial proliferation. After treatment with EEO-CG liners, the rate of increase in TVC of fish fillets decreased further. This is because volatile components in EEO, such as 1,8-cineole, can disrupt the cell membrane structure of microorganisms, thus inhibiting bacterial growth. However, due to the high volatility and rapid release of essential oils, their antibacterial effect weakened in the later stages of storage. Compared to CG liners, ZIF-CG liners also exhibited better antibacterial performance. This is because ZIF materials themselves possess certain antibacterial activity, and their porous structure can form a physical barrier within the membrane matrix, inhibiting microbial migration and colonization. In contrast, the TVC value of fish fillets treated with EEO@ZIF-CG liners increased most slowly, reaching the acceptable limit only on day 7.5. This is mainly attributed to the effective encapsulation and sustained release of eucalyptus essential oil by ZIF, allowing the active components of the essential oil to be continuously released during storage, producing a synergistic antibacterial effect with ZIF. Meanwhile, the excellent water absorption of the liner reduces the accumulation of fish fillet exudate on the surface of the fillets, further inhibiting microbial growth and thus significantly delaying the microbial spoilage process of the fillets, extending the shelf life of the fillets from 4.5 days to 7.5 days.

[0064] (3) Effect of liner on TBA value of sea bass fillets: 10.00g of fish fillet was placed in a beaker and 25.00mL of deionized water was added. The sample was homogenized, and then 25mL of 5% ( m / V A solution of trichloroacetic acid was prepared, stirred rapidly until homogeneous, and allowed to stand for 30 minutes. The solution was then filtered, and 5 mL of the supernatant was transferred to a colorimetric tube. 5 mL of 2% ( m / V The absorbance of a TBA (thiobarbituric acid) solution was measured at 532 nm after heating in a water bath at 90 °C for 30 min, rapidly cooling to room temperature.

[0065] The effects of the liners in Examples 1 and 1-4 on the TBA value of sea bass fillets during storage are as follows: Figure 3As shown in the figure, the TBA value is used to assess the degree of fat oxidation, especially the content of malondialdehyde (MDA), a secondary oxidation product, and is an important indicator for measuring the freshness and quality deterioration of fish. During the 15-day storage period, the TBA value of sea bass fillets generally showed an upward trend. The untreated group and the blank liner treatment group increased to 0.360±0.022 mg MDA / kg and 0.217±0.021 mg MDA / kg, respectively, within 6 days before decreasing. This is related to the further decomposition of MDA into other aldehydes, ketones, acids, and other small molecules, or the irreversible cross-linking with proteins and amino acids, indicating that the fish had spoiled to an unacceptable state. Compared with the blank liner, the TBA value of the fillets in the CG liner treatment group increased at a slower rate. This is related to the weak antioxidant properties of the CG film and the liner's absorption of exudate, keeping the fillet surface relatively dry. The CG liner with added EEO further reduced the rate of TBA value increase, which is attributed to the significant antioxidant effect of the essential oil. However, due to the rapid release of the essential oil, the spoilage rate of the fillets accelerated in the later stages. Compared to CG liners, the TBA value of fish fillets treated with ZIF-CG liners increased more slowly but at a higher rate than those treated with EEO-CG liners. This is because ZIF-CG primarily delays lipid oxidation indirectly through physical barrier and juice absorption, lacking the ability to directly scavenge free radicals, while the eucalyptus oil in EEO-CG can directly inhibit the lipid oxidation chain reaction. Fish fillets treated with EEO@ZIF-CG liners maintained the lowest TBA value throughout the entire storage period, exhibiting the best antioxidant performance. This is mainly attributed to the effective encapsulation and sustained release of eucalyptus oil by ZIF-8, allowing for the continuous release of antioxidant active ingredients, and synergistic effects with the physical barrier effect of ZIF itself.

[0066] (4) Effect of the liner on the pH value of sea bass fillets: 5.00g of fish fillet was placed in a beaker and 45.00mL of deionized water was added. The sample was homogenized and allowed to stand for 30min. The pH value was measured using a pH meter (manufacturer: Nikon Ltd., Japan, model: FE20).

[0067] The effect of the liners in Example 1 and Comparative Examples 1-4 on the pH value of sea bass fillets during storage is as follows: Figure 4As shown, the pH value of fish fillets during spoilage initially decreased and then increased with prolonged storage time. In the initial stage, the pH decrease was due to the accumulation of lactic acid and phosphate caused by the consumption of glycogen and ATP. With prolonged storage, the formation of alkaline nitrogenous compounds (such as ammonia and amines) by bacteria and enzymes caused the pH value of the fish fillets to begin to rise after 3 days. Specifically, the pH value of untreated fish fillets decreased most rapidly in the early stage of storage and increased most rapidly in the later stage, reaching a peak of 7.76 on day 15. This was due to the rapid enzymatic reactions and microbial activity within the fish fillets, leading to protein degradation and the accumulation of amino acids and amines, resulting in a rapid increase in pH and severe spoilage. The rate of pH increase was slower in fish fillets treated with a blank liner, indicating that the absorbent layer could absorb the juices produced during spoilage, which was detrimental to microbial growth and slowed down protein degradation and the formation of alkaline nitrogenous compounds. The pH rise rate of fish fillets treated with CG liners was slightly lower than that of fillets without CG liners. This is because the antibacterial properties of the CG film are relatively weak, and its inhibitory effect on spoilage bacteria is limited. The pH change rate of fish fillets treated with EEO-CG liners was further slowed, and the pH remained at a low level in the early stages of storage. This is because the rapid release of EEO effectively inhibited microbial growth and delayed protein decomposition while the liners absorbed the exudate from the fish fillets. The pH change of fish fillets treated with ZIF-CG liners was similar to that of EEO-CG liners. This is because the antibacterial effect of ZIF-8 is limited, relying mainly on the slow release of metal ions and the physical barrier effect, and it failed to significantly slow down the pH rise. Fish fillets treated with EEO@ZIF-CG liners exhibited the best pH stability, with the pH reaching its lowest point on day 6, indicating that protein decomposition in the fish fillets only began after day 6. Therefore, it can be seen that by encapsulating EEO in ZIF-8 particles and then placing them in a composite membrane to construct a two-stage sustained-release system, the release pathway of essential oils can be extended, their sustained-release performance can be improved, and EEO with antibacterial and antioxidant properties can be slowly released during storage, effectively inhibiting the growth of microorganisms and the degradation of proteins in the long term, thereby achieving a long-lasting preservation effect.

[0068] (5) Effect of liner on volatile basic nitrogen (TVB-N) in sea bass fillets

[0069] 5.00 g of fish meat and 37.50 mL of deionized water were homogenized and then filtered through qualitative filter paper with a pore size of 15-20 μm. The filtrate was collected and distilled using a semi-automatic Kjeldahl nitrogen analyzer (manufacturer: Zhengzhou Haineng Instrument Co., Ltd., model: Haineng K9840+SH220F). The solution was then titrated with 0.01 mol / L hydrochloric acid. The volatile basic nitrogen content of the sample was calculated according to GB5009.228-2016.

[0070] The effects of the liners in Examples 1 and 1-4 on the TVB-N value of sea bass fillets during storage are as follows: Figure 5 As shown, proteins and non-protein nitrogenous substances in fish muscle tissue undergo degradation reactions under the action of microbial enzymes, with the main metabolic end product being the accumulation of TVB-N. Therefore, the TVB-N value is also one of the important indicators for measuring the spoilage of fish fillets. Figure 5 It was found that the TVB-N value of all fish fillets increased with prolonged storage time. The untreated group of fish fillets already exceeded 15 mg / 100g on day 8.3, indicating that the fillets were no longer of superior quality. The increase in TVB-N value of fillets treated with blank liner was the second fastest, because the liner absorbed the secreted juices from the fillets, maintaining a dry environment and delaying protein decomposition. Fish fillets treated with CG liner showed a further slowing of TVB-N accumulation compared to those with blank liner. This is because the CG film has a high swelling degree and a certain hygroscopic capacity, which can more effectively reduce the retention of exudate on the surface of the fillets and inhibit the growth of spoilage bacteria. Adding EEO to the CG film further slowed the increase in TVB-N value. This is because the active ingredients in EEO, such as 1,8-cineole, can significantly inhibit the reproduction of spoilage microorganisms and the activity of related proteases, thereby effectively slowing down the formation of volatile alkaline substances such as amines and ammonia. ZIF-CG liners showed better inhibition of TVB-N in fish fillets than CG liners, but were weaker than EEO-CG liners in the early stages. ZIF-8 exhibited some antibacterial activity, primarily dependent on Zn. 2+ While ZIF-8 releases and exhibits surface contact antibacterial effects, direct contact between the ZIF-8 particles and the fish fillets is limited in the composite membrane, resulting in insufficient antibacterial activity and thus limited ability to inhibit TVB-N accumulation. Fish fillets treated with EEO@ZIF-CG liners maintained the lowest TVB-N accumulation rate throughout the storage period, demonstrating optimal preservation. This is primarily attributed to the loading and slow-release effect of ZIF-8 on eucalyptus oil, allowing for continuous EEO release. Combined with the liner's excellent liquid absorption properties, this effectively inhibits the growth of spoilage microorganisms and protein degradation.

[0071] (6) Effect of padding on the textural properties of sea bass fillets

[0072] The fish fillets were cut into 1.5cm×1.5cm×1.5cm pieces, and the hardness, elasticity, chewiness and resilience of the fillets were measured using a texture analyzer (manufacturer: Stable MicroSystems, model: TA-XT-PLUS).

[0073] The effects of the liners in Examples 1 and 1-4 on the textural properties of sea bass fillets during storage are as follows: Figure 6As shown, the textural properties of aquatic products are an important indicator system for evaluating quality. Key parameters include hardness, elasticity, resilience, and chewiness. Changes in these indicators can reflect multi-scale deterioration mechanisms such as the integrity of muscle tissue protein structure, lipid oxidation state, and water migration patterns. With prolonged storage, the textural properties of all fish fillets decreased. This is due to the rapid protein degradation after fish death, the separation of muscle fibers from the diaphragm, and the further degradation of actin and desensitizing proteins, which further damages the texture of the fillets. The untreated group of fish fillets showed the fastest decline in all textural indicators. During storage, severe surface liquid accumulation led to rapid microbial proliferation, damage to myofibril structure, and accelerated protein degradation, resulting in a rapid decrease in hardness and chewiness. Simultaneously, elasticity and resilience were significantly weakened, indicating that the fish meat lost its original dense and elastic structure. The rate of textural degradation slowed in the blank liner treatment group. This is related to the liner absorbing exudate, reducing surface water activity, decreasing nutrients in the juice, and preventing the large-scale proliferation of microorganisms. However, due to its lack of antibacterial and antioxidant functions, the inhibition of microbial and enzymatic degradation was limited, and the textural indicators continued to decline. Compared to blank liners, CG liners performed slightly better in maintaining the texture of fish fillets. Their weak antibacterial properties and good hygroscopicity helped delay tissue deterioration. EEO-CG liners significantly delayed the decline of various texture parameters in the early stages of storage. This is because the eucalyptus oil in the coating was released rapidly, effectively inhibiting microbial growth and reducing protease activity. At the same time, its antioxidant effect reduced the damage of lipid oxidation to muscle cell membranes and protein structures. ZIF-CG liners provided better protection for the texture of fish fillets than CG liners. This is because ZIF-8 inhibited the growth of some putrefactive bacteria and slowed down the degradation rate of myofibril and collagen proteins, thereby maintaining the mechanical support structure of the fish. However, due to its limited antioxidant capacity, it was insufficient in inhibiting lipid oxidation-induced structural damage, resulting in limited texture preservation. Throughout the storage period, the EEO@ZIF-CG liner exhibited the best texture retention effect, with the fish fillets showing significantly higher firmness, elasticity, chewiness, and resilience compared to other treatment groups. This is attributed to the slow release of EEO by ZIF-8, which allows for the continuous release of essential oil active ingredients and works synergistically with the liner's liquid absorption and regulation capabilities to effectively inhibit microbial proliferation and enzymatic degradation, thereby maximizing the maintenance of the integrity of the myofiber network structure.

[0074] (7) Effect of padding on color difference of sea bass fillets

[0075] Three different locations on the surface of the fish fillets were selected, and the surface colorimetric properties of the fish fillets were measured using a portable colorimeter (manufacturer: Konica Minolta, model: CR400). , , value.

[0076] The effect of the padding used in Examples 1 and Comparative Examples 1-4 on the color difference of sea bass fillets during storage is as follows: Figure 7 As shown, where, L Represents brightness, a Representing red and green b Representing yellow and blue. By Figure 7 It can be seen that as the storage time increases, the properties of all samples decrease. L value and a The continuous decline in values ​​caused the surface of the fish fillets to become dull, a phenomenon attributed to moisture loss, protein denaturation, and the accumulation of lipid oxidation products. b The color difference value showed an upward trend, which is the result of the reaction between secondary products of lipid oxidation (such as aldehydes) and proteins, and is also the main cause of the yellowing of fish fillets. The untreated group of fish fillets showed the largest variation in color difference value, indicating a large accumulation of exudate on the surface of the fillets, providing favorable conditions for microbial growth, accelerating myoglobin oxidation and lipid peroxidation, and consequently causing darkening, fading, and significant yellowing of the flesh. After treatment with blank liners, the color difference value of the fish fillets slowed down, because the liners' absorption of exudate improved the packaging microenvironment; however, the liners lacked antibacterial and antioxidant functions, and were still unable to effectively inhibit pigment production and lipid oxidation. The color difference value of the fish fillets treated with CG liners showed the second largest variation, mainly because the CG film has a high swelling degree, which can absorb the exudate from the fish fillets, thereby reducing microbial growth and indirectly delaying myoglobin oxidation and color deterioration. Compared with CG liners, the introduction of essential oils resulted in EEO-CG liners improving the color difference of the fish fillets throughout the entire storage period. L The value decreased slowly. a The value remained relatively good. b The increase in color difference was significantly suppressed, indicating that the active ingredients in the essential oil can effectively scavenge free radicals and inhibit lipid oxidation, while simultaneously enhancing the antibacterial effect, thus synergistically delaying the color deterioration of fish fillets. The degree of color difference change in fish fillets treated with ZIF-CG liner was between that of CG and EEO-CG, indicating that the antibacterial effect of ZIF-8 can inhibit microbial growth to a certain extent and slow down color deterioration; however, its inhibitory effect on lipid oxidation is relatively limited. b The values ​​still showed a relatively obvious upward trend. However, after treatment with EEO@ZIF-CG liners, the fish fillets exhibited the smallest variation in color difference values ​​throughout the entire storage period. L 、a and b All remained at a relatively high level. This is due to the loading and sustained-release effect of ZIF-8 on essential oils, which allows for the stable and continuous release of the active ingredients in the essential oils, forming a long-term effective antibacterial and antioxidant environment. This significantly delays myoglobin oxidation and lipid peroxidation, thus maximizing the preservation of the overall color of the fish fillets.

[0077] (8) The effect of padding on the appearance of sea bass fillet photographs

[0078] Inside the clean bench, photos of fish fillets were taken with a mobile phone on days 0, 3, 6, 9, 12, and 15.

[0079] The effect of the padding in Example 1 and Comparative Examples 1-4 on the appearance of sea bass fillets during storage is shown in the photographs. Figure 8 As shown, A is the untreated group, B is the blank pad, C is the CG pad, D is the EEO-CG pad, E is the ZIF-CG pad, and F is the EEO@ZIF-CG pad. The appearance of the fish fillets can more intuitively show the state of spoilage, such as... Figure 8As shown, at day 0, all fish fillets were translucent or milky white with a glossy surface, clear muscle fiber texture, and no mucus secretion. During storage, the untreated group of fish fillets rapidly showed significant exudate accumulation on the surface, the muscle tissue gradually loosened, and the color changed from initially bright to dull and grayish, later accompanied by a slimy feel and obvious signs of spoilage. Rapid microbial reproduction and enhanced endogenous enzyme activity led to myofibril protein degradation and decreased water retention capacity. The exudation phenomenon on the surface of the fish fillets treated with blank pads was alleviated, and the overall integrity was better than that of the untreated group samples, but with prolonged storage, tissue loosening and decreased gloss were still observed. The fish fillets treated with CG pads maintained a relatively intact appearance, with delayed surface gloss reduction and tissue softening. The CG membrane absorbed the exudate, slowing down the metabolic activity of spoilage microorganisms and delaying tissue structure destruction to some extent, but significant deterioration still occurred in the later stages. Fish fillets treated with EEO-CG maintained a relatively dry surface, firm muscle structure, and good color retention throughout the storage period, exhibiting significantly superior quality compared to samples treated with CG pads. The addition of essential oils not only enhanced the antibacterial effect but also effectively delayed the deterioration of appearance by inhibiting lipid oxidation and protein denaturation. Fish fillets treated with ZIF-CG pads deteriorated more slowly than those treated with CG pads, but yellowed faster than those treated with EEO-CG pads. While ZIF-8's antibacterial activity inhibited the growth of some microorganisms, its antioxidant capacity was limited, resulting in noticeable darkening of the color later on. EEO@ZIF-CG pads showed the best effect in maintaining the appearance quality of fish fillets throughout the entire storage period, with no significant exudate accumulation or yellowing on the surface. This result is attributed to the encapsulation and sustained release of essential oils by ZIF-8, allowing for sustained antibacterial and antioxidant activity, thereby synergistically inhibiting microbial growth, protein degradation, and oxidation reactions. This is consistent with the results of the color difference study, indicating that EEO@ZIF-CG pads effectively delay the discoloration of fish fillet surfaces.

[0080] (9) The effect of padding on the water-holding capacity of sea bass fillets

[0081] Weigh 5.00g of fish fillet, wrap it in filter paper, and record this as W1. Centrifuge at 4000rpm for 10min, and record this as W2. Calculate the water-holding capacity (WHC) of the sample using Equation 1: WHC (%) = W1 / W2 × 100% Equation 1 The effects of the liners in Examples 1 and 1-4 on the water-holding capacity of sea bass fillets during storage are as follows: Figure 9 As shown, water-holding capacity (WHC) is a key indicator of a fish's ability to retain moisture, directly affecting its texture, mouthfeel, and quality stability. The decrease in WHC of sea bass fillets during refrigeration is mainly caused by protein denaturation, microbial activity, and oxidative damage. Figure 9It was observed that the water content (WHC) of the fish fillets decreased continuously with prolonged storage, with the untreated group showing the fastest decline. This indicates rapid spoilage during storage, with bacterial enzymatic hydrolysis disrupting the cross-linking structure between proteins and water. After treatment with a blank liner, the rate of WHC decline slowed. This is because the liner's absorbent properties reduce the accumulation of juices on the fillet surface, but it cannot inhibit protein structural degradation, thus limiting its effectiveness in maintaining internal muscle moisture. The water-holding capacity of the CG-lined fillets was significantly higher than that of the untreated and blank-lined groups. This is related to the absorption of fish juices by the CG membrane, indicating that this effect can delay the degradation of myofibril proteins, reduce muscle tissue structural damage, and thus maintain water-binding capacity to some extent. The EEO-CG-lined fillets exhibited higher water-holding capacity throughout the entire storage period, attributed to the essential oil's ability to inhibit microbial and enzyme activity, thereby delaying protein denaturation. The water-holding capacity of fish fillets treated with ZIF-CG liners was better than that of CG liners, but slightly lower than that of EEO-CG liners. This is because the antibacterial activity of ZIF-8 effectively inhibited the growth of some microorganisms, thereby delaying protein degradation. However, its antioxidant capacity was relatively limited, resulting in significant water loss from the fish fillets in the later stages. The EEO@ZIF-CG liner treatment showed the best effect in maintaining the water content (WHC) of the fish fillets, indicating that the long-term release of essential oils can effectively reduce microbial proliferation, protein denaturation, and oxidative damage, achieving long-term freshness preservation of the fish fillets.

[0082] (10) Effect of padding on muscle tissue structure of sea bass fillets

[0083] Cut the fish fillets into 1.0cm×1.0cm×1.0cm cubes and freeze them in a -80℃ freezer. Use a cryostat (manufacturer: Leica GmbH, Germany, model: CM1850) to slice the fish pieces into thin slices. Stain with a hematoxylin-eosin (HE) kit (Beijing Solarbio Science & Technology Co., Ltd.). Observe under an optical microscope (manufacturer: Nikon Ltd., Japan, model: 80-i) at 40x magnification and take pictures.

[0084] The effects of the liners in Examples 1 and 1-4 on the muscle tissue structure of sea bass fillets during storage are as follows: Figure 10 As shown, A is the untreated group, B is the blank pad, C is the CG pad, D is the EEO-CG pad, E is the ZIF-CG pad, and F is the EEO@ZIF-CG pad. After fish death, the initial changes in muscle are due to the activity of endogenous enzymes, which promote the gradual decomposition of muscle proteins, connective tissue, and fat proteins. For example... Figure 10As shown, the muscle fibers of fresh fish fillets are tightly packed. With prolonged storage, the intermuscular gaps in all fillets tend to increase. By day 6 of storage, the gaps between the muscle fibers in untreated fillets are wider than in other samples, and muscle fiber breakage is observed. By day 15 of storage, the muscle arrangement of untreated fillets is severely loose, and the structure has collapsed. This is mainly due to the massive proliferation of microorganisms and enhanced activity of endogenous proteases, leading to severe degradation of myofibril proteins, disruption of intercellular connections, and consequently, significant water loss and rapid softening of the texture. The muscle structure deterioration of fillets treated with blank liners is slightly less severe than that of untreated fillets, but they still exhibit muscle fiber swelling, increased gaps, and localized breakage. This indicates that while the blank liners absorb exudate to some extent and improve the packaging microenvironment, they fail to effectively inhibit protein degradation and tissue structure damage. Compared to blank liners, the muscle tissue structure of fillets treated with CG liners is relatively intact, with significantly reduced breakage and collapse. This is mainly attributed to the fact that the CG membrane's absorption of the fish fillet's exudate slows down the growth of putrefactive bacteria and protease activity, thereby delaying the destruction of myofibril structure. Fish fillets treated with EEO-CG liner maintained better muscle structure than those treated with CG liner; the muscle fibers were more regular in shape, densely packed, and had smaller interfiber gaps. This is attributed to the synergistic inhibition of microbial metabolism and lipid oxidation by the essential oils, reducing oxidative stress damage to protein structure and helping to maintain the stability of the muscle microstructure. Fish fillets treated with ZIF-CG liner showed better muscle tissue integrity than those treated with CG liner, but slight fiber loosening was still observed in some areas. This indicates that ZIF-8's antibacterial properties effectively delayed the degradation of fish fillet muscle fibers, but due to its limited antioxidant capacity, a certain degree of protein oxidation and structural damage still occurred in the later stages of storage. The fish fillets treated with EEO@ZIF-CG retain the most intact muscle tissue structure, with slightly widened muscle gaps and minor adhesion, but almost no obvious breakage or collapse. This is thanks to the slow-release effect of ZIF-8 on essential oils, which allows antibacterial and antioxidant activities to continue to be exerted during storage, effectively inhibiting microbial erosion and protein oxidation, thereby maintaining the integrity of the muscle tissue to the greatest extent.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an EEO@ZIF-8 / CG composite membrane, characterized in that, It includes the following steps: 1) Add zinc salt aqueous solution to 2-methylimidazole aqueous solution, and sequentially allow to stand, centrifuge and dry to obtain ZIF-8 particles; 2) After ultrasonically mixing ZIF-8 granules and eucalyptus oil, the mixture was centrifuged and dried sequentially to obtain EEO@ZIF-8 granules; 3) After mixing the gelatin solution, chitosan solution, glycerol and EEO@ZIF-8 particles, the mixture is stirred, sonicated and dried in sequence to obtain the EEO@ZIF-8 / CG composite membrane.

2. The preparation method according to claim 1, characterized in that, Step 1) The zinc salt aqueous solution is a zinc acetate aqueous solution or a zinc sulfate aqueous solution, the concentration of the zinc salt aqueous solution is 9~23 g / L, and the volume ratio of the zinc salt aqueous solution to the 2-methylimidazole aqueous solution is 8~12:16~24; when the zinc salt aqueous solution is a zinc acetate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is 135~155 g / L; when the zinc salt aqueous solution is a zinc sulfate aqueous solution, the concentration of the 2-methylimidazole aqueous solution is 175~185 g / L.

3. The preparation method according to claim 1 or 2, characterized in that, Step 1) The settling time is 22-26 hours, the centrifugation speed is 6000-8000 rpm, and the centrifugation time is 3-7 minutes; the drying temperature is 55-65℃, and the drying time is 22-26 hours; after centrifugation, the white precipitate is collected, washed with water, and then dried, and the washing is performed 2-4 times.

4. The preparation method according to claim 3, characterized in that, Step 2) The mass ratio of ZIF-8 particles to eucalyptus oil is 1:1.8~2.2; the ultrasonic mixing frequency is 45~55kHz, and the ultrasonic mixing time is 25~35min; the centrifugation speed is 6000~8000rpm, and the centrifugation time is 3~7min; the drying temperature is 45~55℃, and the drying time is 1.5~2.5h; after centrifugation, the product is washed and then dried, and the washing reagent is anhydrous ethanol, and the number of washings is 2~4 times.

5. The preparation method according to claim 4, characterized in that, In step 3), the volume ratio of the gelatin solution to the chitosan solution is 2.5~3.5:1.5~2.5, the mass of glycerol is 18~22% of the total mass of gelatin and chitosan, and the mass of EEO@ZIF-8 particles is 4~6% of the total mass of gelatin and chitosan. The gelatin solution has a mass concentration of 45-55 g / L and is in water as the solvent; the chitosan solution has a mass concentration of 17-23 g / L and is in acetic acid solution with a mass fraction of 0.8-1.2%.

6. The preparation method according to claim 5, characterized in that, Step 3) The stirring time is 22~26h, the drying temperature is 20~30℃, and the drying time is 45~52h.

7. The EEO@ZIF-8 / CG composite membrane prepared by the preparation method according to any one of claims 1 to 6.

8. An EEO@ZIF-CG composite film preservation liner comprising the EEO@ZIF-8 / CG composite film of claim 7, characterized in that, The EEO@ZIF-CG composite film preservation liner consists of, from bottom to top, an absorbent bottom layer, an EEO@ZIF-8 / CG composite film, and a super-dual-hydrophobic mesh film.

9. The EEO@ZIF-CG composite film preservation liner according to claim 8, characterized in that, The absorbent bottom layer consists of non-woven fabric, absorbent cotton, bentonite, and non-woven fabric in that order from bottom to top.

10. The application of the EEO@ZIF-CG composite film preservation liner according to claim 9 in the preservation of sea bass.

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