Preservative film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of food packaging, and particularly relates to a preservative film and a preparation method and application thereof. Citric acid is adopted to replace toxic organic ligands in traditional MOFs, safe and nontoxic Zn-CA MOF is synthesized in situ with a zinc ion source, the CO2 / O2 separation coefficient and gas permeability of the composite membrane can be improved at the same time through the high specific surface area and the porous structure of the Zn-CA MOF, and the problem that a pure PBAT membrane is insufficient in gas regulation and control capacity is accurately solved; secondly, ATBC is introduced as a compatibilizer, the compatibility of the Zn-CA MOF and a PBAT matrix is effectively improved, the Zn-CA MOF is uniformly dispersed in a PBAT / ATBC system in cooperation with an in-situ growth method, and performance fluctuation caused by agglomeration of the MOFs is avoided. Based on the composite material, the balance controlled atmosphere fruit packaging film is prepared through a melting tape casting method, and an active controlled atmosphere technology is innovatively combined, so that a dual fresh-keeping mechanism of initial precise gas distribution and subsequent dynamic regulation and control is formed.

Description

Technical Field

[0001] This application belongs to the field of food packaging technology, specifically relating to a food preservation film with Zn-CA MOF metal-organic framework material, polybutylene terephthalate (PBAT), and tributyl acetyl citrate (ATBC) as the main components. Background Technology

[0002] Polybutylene terephthalate (PBAT), a biodegradable thermoplastic material copolymerized from terephthalic acid, adipic acid, and butanediol, has shown broad application potential in the food packaging field due to its excellent thermal stability, good flexibility, and processing adaptability. Its molecular chain combines rigid terephthalate units with flexible adipicate units, giving the material excellent film-forming properties and mechanical toughness, meeting the basic requirements for food preservation films. Furthermore, PBAT can be completely degraded by microorganisms in natural soil environments, effectively solving the pollution problems caused by traditional plastic food preservation films, aligning with the development trend of environmentally friendly packaging. However, the relatively loose molecular chain structure of PBAT, with numerous disordered pores, results in poor gas separation performance, making it difficult to precisely control the respiration of fruits and vegetables and providing a suitable modified atmosphere environment for fresh products, thus limiting its application in high-requirement preservation scenarios.

[0003] To improve the gas separation performance of PBAT, researchers have developed various modification schemes, among which polymer blending modification has been widely studied due to its simple process and stable effect. Patent application number 202411281636.8 discloses a preparation technology for a PBAT composite biodegradable modified atmosphere film. This scheme involves blending a self-made copolyester PBTF with PBAT at a mass ratio of 1% to 5%, preparing a casting solution using dichloromethane as a solvent, and then forming a composite film through processes such as casting and drying. The furan ring structure in the PBTF molecule synergistically interacts with the PBAT molecular chain, densifying the film structure through molecular chain entanglement and hydrogen bonding. Simultaneously, the synergistic crystallization effect of both further reduces the gas permeation channels. Experimental data show that the O2 permeability of this composite film is significantly improved from approximately 600 cm⁻¹ of pure PBAT. 3 / m 2 • 24h • 0.1MPa decreased to 300cm 3 / m 2 With an oxygen permeability of less than 0.1 MPa for 24 hours, the low O2 permeability effectively reduces the entry of external oxygen into the packaging, significantly inhibits the aerobic respiration of fruits and vegetables, and extends the storage time of fresh products such as cherries.

[0004] However, this blending modification scheme still has obvious shortcomings: the modified atmosphere film prepared by blending PBTF and PBAT has achieved an effective reduction in oxygen permeability, but carbon dioxide permeability has decreased simultaneously. It has not achieved its claimed core function of high carbon dioxide permeability and low oxygen permeability, and deviates from the gas selectivity control target required for ideal modified atmosphere preservation. Summary of the Invention

[0005] The purpose of this application is to provide a food preservation film with high carbon dioxide permeability and low oxygen permeability, which is achieved through the following technical solution:

[0006] A method for preparing a food preservation film includes the following steps: dissolving a zinc ion source and a citric acid ligand separately in an organic solvent, then sequentially adding them to an organic blend of PBAT / ATBC to promote a coordination reaction between zinc ions and the citric acid ligand; and obtaining a PBAT / ATBC@Zn-CA solid material after washing with alcohol and drying. The concentration of PBAT in the organic blend is 40-60 g / L, and the concentration of ATBC in the organic blend is 2-3 g / L. The molar ratio of the citric acid ligand to the zinc ions in the zinc ion source is (6-12):1, and the total mass of both added is 0.2-0.8% of the total mass of PBAT and ATBC.

[0007] Preferably, the zinc ion source is zinc nitrate hexahydrate; the concentration of zinc nitrate hexahydrate dissolved in an organic solvent is 0.08~0.15 mol / L.

[0008] Preferably, the concentration of the citric acid ligand dissolved in the organic solvent is 0.5~1 mol / L.

[0009] Preferably, the process also includes a film-forming step: using the PBAT / ATBC@Zn-CA solid material as raw material, a preservation film is prepared by melt casting.

[0010] Preferably, the process parameters for the melt casting method are: melting temperature 130~150℃, screw speed 20~40rpm.

[0011] A food preservation film prepared using any one of the above-described preparation methods.

[0012] The above-mentioned applications of plastic wrap in food preservation.

[0013] Preferably, the application includes the following steps: placing the food into a packaging container made of the cling film, filling the packaging with an initial gas using a modified atmosphere packaging machine, and then sealing it; the initial gas consists of 4-6% CO2, 5-8% O2, and the remainder is N2.

[0014] Compared with the prior art, this application has the following beneficial effects:

[0015] This application is based on biodegradable PBAT. On the one hand, it overcomes the shortcomings of pure PBAT membranes, such as low CO2 / O2 separation coefficient and insufficient gas control capability. By replacing the toxic organic ligands in traditional MOFs with citric acid, a safe and non-toxic Zn-CA MOF is synthesized in situ with zinc ions. Its high specific surface area and porous structure not only significantly improve the CO2 / O2 separation coefficient of the composite membrane, but also enhance CO2 permeability, achieving the ideal modified atmosphere characteristics of high CO2 permeability and low O2 permeability, thus avoiding the problem that traditional PBAT membranes cannot accurately control the respiratory environment of fruits and vegetables. On the other hand, it solves the risk of CO2 accumulation caused by the low permeability of existing PBAT / copolyester blend membranes (such as PBAT / PBTF). Through the selective permeation effect of Zn-CA MOF, it ensures rapid CO2 discharge to avoid damage to fruits and vegetables, while inhibiting O2 entry to slow down respiratory metabolism, thus making up for the shortcomings of insufficient gas selectivity in traditional blending modification schemes.

[0016] Meanwhile, this application utilizes ATBC as a compatibilizer to effectively improve the compatibility between Zn-CA MOF and the PBAT matrix. Combined with in-situ growth, this ensures uniform dispersion of Zn-CA MOF within the system, avoiding performance fluctuations caused by MOF aggregation and guaranteeing the membrane's mechanical stability and gas permeation uniformity. Ethyl acetate is used as a solvent, replacing toxic reagents such as chloroform, thus enhancing the material's food contact safety and environmental friendliness. Furthermore, this application combines the composite membrane with active modified atmosphere packaging (MAP) technology, introducing initial gases of 4-6% CO2 and 5-8% O2, forming a dual guarantee of precise initial gas mixing and subsequent dynamic control. Compared to pure active or pure balanced MAP technologies, this method is better suited to the preservation needs of high-respiration-intensity fruits such as cherry tomatoes and strawberries. Experiments have demonstrated that this method can significantly inhibit the respiration rate of fruits and vegetables, slow down the growth of total bacterial count, effectively maintain the nutritional components and sensory quality of fresh products, and the membrane material is biodegradable. Balancing preservation effect, safety, and environmental friendliness, this method has broad application prospects. Attached Figure Description

[0017] The attached diagram will be briefly described below:

[0018] Figure 1 This is a comparison chart of the gas permeability test results of the PBAT / ATBC@Zn-CA composite balanced modified atmosphere fruit packaging film and other packaging films according to an embodiment of the present invention.

[0019] Figure 2 This is a comparison chart of the gas permeability coefficient and CO2 / O2 separation coefficient test results of the PBAT / ATBC@Zn-CA composite balanced modified atmosphere fruit packaging film of this invention with other packaging films;

[0020] Figure 3This is a comparison graph showing the changes in respiration rate of modified atmosphere packaging preservation method and control group cherry tomatoes before and after storage, according to an embodiment of the present invention.

[0021] Figure 4 This is a comparison graph showing the changes in total bacterial count before and after storage between the modified atmosphere packaging preservation method of this invention and the control group of cherry tomatoes. Detailed Implementation

[0022] The present application will now be further described by way of specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. Furthermore, the embodiments of the present application described below are generally only a part of the embodiments of the present application, and not all of the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort should fall within the scope of protection of the present application.

[0023] Example 1

[0024] This embodiment discloses a modified atmosphere packaging method for preserving fruit, including the following steps:

[0025] S1. Preparation of PBAT / ATBC@0.2Zn-CA composite material by in-situ growth method: 50g PBAT and 2.632g ATBC were dissolved in 1000mL ethyl acetate to make the mass of ATBC 5% of PBAT, thus obtaining a PBAT / ATBC blend solution; 12.6mg Zn(NO3)2·6H2O was dissolved in 5mL ethyl acetate to obtain solution A; 405.2mg CA was dissolved in 10mL ethyl acetate to obtain solution B. The molar ratio of zinc ions to CA was 1:10. Solution A was then slowly added dropwise to the PBAT / ATBC blend solution and stirred for 0.5h. Then solution B was added and stirred for 0.5h. The mixture was allowed to stand for 12h to ensure the synthesis of Zn-CA MOF. The mass of Zn-CA was 0.2% of the total mass of PBAT and ATBC. The mixture was then washed three times with anhydrous ethanol and vacuum dried for 6h to obtain the PBAT / ATBC@0.2Zn-CA composite material.

[0026] S2. Preparation of PBAT / ATBC@0.2Zn-CA film by melt casting: The PBAT / ATBC@0.2Zn-CA composite material prepared in S1 was used to form a film by a twin-screw extruder. The melting temperature was set to 140℃, the screw speed to 30rpm, the cooling roller temperature to 40℃, and the traction speed to 3m / min. A PBAT / ATBC@0.2Zn-CA film with a thickness of 70µm was obtained.

[0027] S3. Inflate the packaging with the initial gas of the internal environment through a modified atmosphere packaging machine: Adjust the gas filling ratio of the modified atmosphere packaging machine to 4% CO2, 6% O2, and 90% N2, and seal the packaging with the PBAT / ATBC@Zn-CA film prepared in S2.

[0028] Example 2

[0029] The difference between this embodiment and Embodiment 1 is the Zn-CA loading. In this embodiment, the Zn-CA mass is 0.4% of the total mass of PBAT and ATBC, and the resulting membrane is denoted as PBAT / ATBC@0.4Zn-CA membrane.

[0030] Example 3

[0031] The difference between this embodiment and Embodiment 1 is the Zn-CA loading. In this embodiment, the Zn-CA mass is 0.6% of the total mass of PBAT and ATBC, and the resulting membrane is denoted as PBAT / ATBC@0.6Zn-CA membrane.

[0032] Example 4

[0033] The difference between this embodiment and Embodiment 1 is the Zn-CA loading. In this embodiment, the Zn-CA mass is 0.8% of the total mass of PBAT and ATBC, and the resulting membrane is denoted as PBAT / ATBC@0.8Zn-CA membrane.

[0034] Comparative Example 1

[0035] This comparative example uses PBAT film as the packaging film, which is made from pure PBAT particles by melt casting and has a film thickness of 70µm.

[0036] Comparative Example 2

[0037] This comparative example uses PBAT film as the packaging film, which is made from pure PBAT granules through melt casting. The film thickness is 70µm. The modified atmosphere packaging machine's inflation ratio is adjusted to 4% CO2, 6% O2, and 90% N2, and the film is then sealed with PBAT film. The only difference between this comparative example and Comparative Example 1 is that Comparative Example 1 did not undergo modified atmosphere packaging.

[0038] Performance Test 1

[0039] Carbon dioxide and oxygen permeability test of composite balanced controlled atmosphere membrane

[0040] This performance test evaluates the carbon dioxide and oxygen permeability of the PBAT membrane and PBAT / ATBC@Zn-CA membrane used in the examples and comparative examples. The method for determining carbon dioxide and oxygen permeability is as follows: the prepared membrane is cut into a circle with a diameter of 9 cm, and the membrane thickness is measured. The gas permeability of the membrane for carbon dioxide and oxygen is tested using a gas permeability tester via the differential pressure method. The power is turned on, the temperature controller is adjusted to 23±0.5℃, the gas pressure regulator is adjusted to 0.4 MPa, sealing oil is applied around the membrane, the membrane is clamped, the program parameters are adjusted, the modified atmosphere membrane thickness value is input, and the test is performed. Figure 1 , 2 As shown, the gas permeability and CO2 / O2 separation coefficient of the PBAT / ATBC@Zn-CA membrane are both increased compared to the PBAT membrane. The gas permeability and CO2 / O2 separation coefficient of the PBAT / ATBC@Zn-CA membrane first increase and then decrease with the increase of Zn-C loading. By controlling its loading, it can be used to prepare packaging suitable for various high-breathing fruits. Among them, the CO2 / O2 separation coefficient of the PBAT / ATBC@0.4Zn-CA membrane is 6~7, which is suitable for cherry tomatoes.

[0041] Performance Test 2

[0042] Test on the preservation effect of composite balanced atmosphere modified film

[0043] This performance test used the modified atmosphere packaging methods of the examples and comparative examples to package cherry tomatoes. The PBAT films of Comparative Examples 1 and 2 served as the control group, while the PBAT / ATBC@Zn-CA film served as the experimental group, verifying its preservation effect. The specific experimental scheme is as follows:

[0044] S1. Preservation Treatment: Select 500 cherry tomatoes of uniform size, free from rot, pests, and mechanical damage from the same batch of ripe tomatoes. Wash them with deionized water and air dry them at room temperature. Divide them into 6 groups. Group ① is directly packaged with PBAT film and is designated as Group CK. The remaining 5 groups are filled with 4% CO2, 6% O2, and 90% N2 in a modified atmosphere packaging machine as the initial gas environment inside the cherry tomato packaging. The following types of films are used for sealing and packaging: PBAT film, PBAT / ATBC@0.2Zn-CA film, PBAT / ATBC@0.4Zn-CA film, PBAT / ATBC@0.6Zn-CA film, and PBAT / ATBC@0.8Zn-CA film, designated as Groups M0, M0.2, M0.4, M0.6, and M0.8, respectively.

[0045] S2. The treated cherry tomatoes were stored in a ventilated storage box at 25°C. The respiration rate and total bacterial count of each group of cherry tomatoes were measured on days 0, 5, 10, 15 and 20 to study the quality changes of cherry tomatoes during the preservation process.

[0046] The respiration rate of cherry tomatoes was measured using a respiration rate meter. After powering on, the air pump and respiration chamber were turned on and preheated for 30 minutes. Once the CO2 concentration displayed on the screen stabilized, the weighed cherry tomatoes were transferred into the respiration chamber, the chamber was quickly closed, and the respiration rate was measured. Figure 3 As shown, the respiration rate of cherry tomatoes in group M0 was lower than that in group CK, indicating that the initial suitable gas environment helps to suppress the respiration rate of cherry tomatoes. The respiration rates of cherry tomatoes in groups M0.2, M0.4, M0.6, and M0.8 were lower than those in groups CK and M0 during storage, indicating that the improvement of the CO2 / O2 separation coefficient can effectively suppress the respiration rate of cherry tomatoes. Among them, the CO2 / O2 separation coefficient of group M0.4 is the most suitable for cherry tomatoes, which can maintain a low respiration rate and prolong their preservation effect.

[0047] Referring to GB4789.2-2022, the change in total bacterial count during the storage of cherry tomatoes was determined. Four cherry tomatoes were placed in a sterile sampling bag, crushed using a homogenizer, and 5g was transferred to another sterile sampling bag. 45mL of sterile physiological saline was added and the mixture was homogenized to prepare a 1:10 sample homogenate. Three 10-fold dilutions were prepared. 1mL of the sample homogenate was poured into sterile petri dishes, with two petri dishes prepared for each dilution. Simultaneously, 1mL of blank dilution was added to two sterile petri dishes as blank controls. 15mL-20mL of plate counting agar, cooled to 46℃-50℃, was poured into the petri dishes immediately, and the dishes were rotated to mix thoroughly. After the agar solidified, the plates were inverted and incubated at 37℃ for 48 hours. Figure 4 As shown, the total number of colonies in cherry tomatoes in group M0 was lower than that in group CK during storage, indicating that a suitable initial gaseous environment helps to delay the spoilage of cherry tomatoes. The total number of colonies in cherry tomatoes in groups M0.2, M0.4, M0.6, and M0.8 was lower than that in groups CK and M0 during storage, indicating that maintaining a low respiration rate can delay the spoilage of cherry tomatoes and prolong their preservation effect.

Claims

1. A method for preparing a food preservation film, characterized in that, Includes the following steps: Zinc ion source and citric acid ligand were dissolved separately in organic solvents and then added sequentially to an organic blend of PBAT / ATBC to promote a coordination reaction between zinc ions and citric acid ligands. After washing with alcohol and drying, PBAT / ATBC@Zn-CA solid material was obtained. The concentration of PBAT in the organic blend was 40-60 g / L, and the concentration of ATBC in the organic blend was 2-3 g / L. The molar ratio of citric acid ligand to zinc ions in the zinc ion source was (6-12):1, and the total mass of both added was 0.2-0.8% of the total mass of PBAT and ATBC.

2. The method for preparing a food preservation film according to claim 1, characterized in that, The zinc ion source is zinc nitrate hexahydrate; the concentration of zinc nitrate hexahydrate dissolved in an organic solvent is 0.08~0.15 mol / L.

3. The method for preparing a food preservation film according to claim 1, characterized in that, The concentration of the citric acid ligand dissolved in the organic solvent is 0.5~1 mol / L.

4. The method for preparing a food preservation film according to claim 1, characterized in that, It also includes a film-forming step: using the PBAT / ATBC@Zn-CA solid material as raw material, a preservation film is prepared by melt casting method.

5. The method for preparing a food preservation film according to claim 4, characterized in that, The process parameters for the melt casting method are: melting temperature 130~150℃, screw speed 20~40rpm.

6. A food preservation film prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the plastic wrap according to claim 6 in food preservation.

8. The application according to claim 7, characterized in that, The application The process includes the following steps: placing the food into a packaging container made of the plastic wrap, filling the packaging with an initial gas using a modified atmosphere packaging machine, and then sealing it; the initial gas consists of 4-6% CO2, 5-8% O2, and the remainder is N2.

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