Metal-organic framework composite fiber film designed based on electrostatic spinning process, preparation method of metal-organic framework composite fiber film and application of metal-organic framework composite fiber film in preservation

Abstract

The invention belongs to the technical field of food preservation, and relates to a metal organic framework composite fiber film designed based on an electrostatic spinning process, a preparation method of the metal organic framework composite fiber film and application of the metal organic framework composite fiber film in preservation. The preparation method comprises the following steps: uniformly mixing theanine, eugenol, zinc salt, 2-methylimidazole and a first solvent, and then centrifuging, washing and drying to obtain a metal organic framework compound; uniformly mixing polylactic acid, chitosan oligosaccharide and a second solvent, adding the metal organic framework compound, and uniformly mixing to obtain a mixed solution; and carrying out electrostatic spinning on the mixed solution to obtain the metal organic framework composite fiber film. Natural active ingredients such as L-theanine and eugenol are introduced, and the ingredients not only have excellent antibacterial and antioxidant properties, but also can effectively inhibit reproduction of microorganisms on the surfaces of fruits and vegetables and reduce water evaporation and respiration rates, so that enzymatic browning and aging processes of the fruits and vegetables are delayed.

Description

Technical Field

[0001] The invention belongs to the technical field of food preservation, and relates to a metal organic framework composite fiber film designed based on an electrostatic spinning process, a preparation method thereof, and application thereof in food preservation. Background Art

[0002] In the field of fruit and vegetable preservation, how to effectively extend the storage period of fruits and vegetables and maintain their freshness and nutritional value has always been the core goal. Traditional fruit and vegetable preservation methods mainly include physical methods (such as refrigeration and modified atmosphere packaging), chemical methods (using preservatives) and biological methods (such as using enzymes or natural antibacterial substances). However, these methods all have certain limitations in practical applications.

[0003] Although refrigeration technology can slow down the spoilage of fruits and vegetables to a certain extent, its high energy consumption cost and limited shelf life limit its widespread application. Modified atmosphere packaging technology inhibits the respiration and microbial growth of fruits and vegetables by adjusting the gas composition in the package, but the complex packaging process and high cost also make it difficult to popularize. Although chemical preservatives are effective, they may pose a potential threat to human health, and consumers are increasingly resistant to chemical additives.

[0004] In recent years, with the rapid development of materials science, fruit and vegetable preservation technology has gradually developed in the direction of green, environmentally friendly and efficient. Among them, fresh-keeping films made of natural materials have attracted much attention due to their advantages such as non-toxicity, harmlessness and biodegradability. This type of film can not only effectively block the penetration of external oxygen, carbon dioxide and water molecules, reduce the respiration and water evaporation of fruits and vegetables, but also inhibit the growth of microorganisms and enzymatic browning of fruits and vegetables by adding natural antibacterial and antioxidant ingredients, thereby significantly improving the preservation effect of fruits and vegetables.

[0005] However, the fruit and vegetable fresh-keeping films currently on the market still have many deficiencies in terms of material selection, preparation process, and fresh-keeping effect, such as high material cost, short fresh-keeping time, and poor mechanical properties. Therefore, developing a fruit and vegetable fresh-keeping film that is low in cost, simple to prepare, has a significant fresh-keeping effect, and is environmentally friendly and degradable has become a hot topic and difficulty in current research. The present invention is proposed in this context, aiming to solve the problems of existing fruit and vegetable fresh-keeping films through innovative materials and technical means, and to provide new ideas and methods for the development of the field of fruit and vegetable fresh-keeping. Summary of the invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies in the prior art and to provide a metal-organic framework composite fiber film designed based on an electrospinning process, a preparation method thereof, and its application in preservation. The metal-organic framework composite fiber film provided by the present invention uses natural antibacterial agents and antioxidants, is safe and reliable, and can effectively extend the shelf life of fruits and vegetables.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] The present invention discloses a method for preparing a metal organic framework composite fiber film based on an electrospinning process design, comprising the following steps:

[0009] (1) mixing theanine, eugenol, zinc salt, 2-methylimidazole, and a first solvent, and then centrifuging, washing, and drying to obtain a metal organic framework complex;

[0010] (2) mixing polylactic acid, chitosan oligosaccharide and a second solvent, and then adding the metal organic framework complex prepared in step (1) to mix, to obtain a mixed solution; and electrospinning the mixed solution to obtain a metal organic framework composite fiber film.

[0011] In some embodiments, the zinc salt is any one of zinc chloride and zinc acetate or a combination of both; the first solvent is any one of water and methanol or a combination of both; the second solvent is a mixture of hexafluoroisopropanol and acetic acid in any proportion.

[0012] In some embodiments, preferably, the zinc salt is zinc chloride; the first solvent is water; the second solvent is a mixture of hexafluoroisopropanol and acetic acid in a volume ratio of 6 to 9:1 to 4, and more preferably a mixture of hexafluoroisopropanol and acetic acid in a volume ratio of 8:2.

[0013] In some embodiments, in step (1), the molar ratio of theanine to eugenol, zinc salt, and 2-methylimidazole is 1-2:1-2:1-2:6-8.

[0014] In some embodiments, preferably, in step (1), the molar ratio of theanine to eugenol, zinc salt, and 2-methylimidazole is 1:1:1:8.

[0015] There is no special requirement for the amount of the first solvent, as long as the raw materials are dissolved evenly; preferably, 30 to 50 mL of the first solvent is used for 0.174 g to 0.696 g of theanine.

[0016] Wherein, in step (1), the washing solvent is preferably water.

[0017] In some embodiments, in step (1), the mixing is stirred at room temperature in the dark for 20 to 30 hours, preferably 24 hours.

[0018] In some embodiments, in step (2), the mass ratio of the polylactic acid to the chitosan oligosaccharide is 1.0-1.5:0.1-0.4; the mass volume ratio of the polylactic acid to the second solvent is 1.0-1.5 g:8-12 mL.

[0019] In some embodiments, preferably, in step (2), the mass ratio of the polylactic acid to the chitosan oligosaccharide is 1.2:0.2; and the mass volume ratio of the polylactic acid to the second solvent is 1.2 g:10 mL.

[0020] In some embodiments, in step (2), the concentration of the metal organic framework complex in the mixed solution is 4% to 16% g / mL.

[0021] In some embodiments, preferably, in step (2), the concentration of the metal organic framework complex in the mixed solution is 5% to 15% g / mL, more preferably 10% to 15% g / mL, and even more preferably 15% g / mL.

[0022] In some embodiments, in step (2), the electrospinning parameters are: receiving distance of 8 to 12 cm, spinning voltage of 14 to 16 kV, ambient humidity of 45% to 50%, and temperature of 20 to 30°C.

[0023] The metal organic framework composite fiber film prepared by the above preparation method is also within the protection scope of the present invention.

[0024] The application of the above metal organic framework composite fiber film in the preparation of food preservative film is also within the protection scope of the present invention.

[0025] Specifically, the food is vegetables and / or fruits.

[0026] Among them, the vegetables include broccoli, lotus root, tomatoes, etc.

[0027] Wherein, the fruits include cherry tomatoes, mangoes, bananas, grapes and the like.

[0028] Wherein, the method for using the cling film is a direct coating method.

[0029] Beneficial effects:

[0030] (1) The fruit and vegetable fresh-keeping film of the present invention is effective in preventing the loss of nutrients such as VC and phenol, and maintains the fresh pH value to a large extent, effectively extending the shelf life of fresh fruits and vegetables.

[0031] (2) The metal organic framework composite fiber film prepared by the present invention adopts natural active substances with antibacterial and antioxidant properties, which are convenient and easy to obtain, green and environmentally friendly, non-toxic and harmless, and the fiber film preparation process conditions are mild, the operation is simple, the error rate is low, and it is suitable for industrial production.

[0032] (3) The present invention introduces natural active ingredients such as L-theanine and eugenol, which not only have excellent antibacterial and antioxidant properties, but also can effectively inhibit the reproduction of microorganisms on the surface of fruits and vegetables, reduce water evaporation and respiration rate, thereby delaying the enzymatic browning and aging process of fruits and vegetables.

[0033] (4) The fruit and vegetable fresh-keeping film of the present invention not only adopts the degradable polymer substrates of polylactic acid and chitosan oligosaccharide, thereby reducing the pollution to the environment, but also has good antioxidant, antibacterial, mechanical properties and mechanical stability, thereby ensuring the performance of the fresh-keeping film. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0035] Figure 1 This is the appearance of Sunshine Rose grapes during a 15-day storage experiment.

[0036] Figure 2 This is the weight loss data of Sunshine Rose grapes after 15 days of storage; where ****P<0.0001.

[0037] Figure 3 This is the pH data of Sunshine Rose grapes after 15 days of storage; among them, **P<0.01, ***P<0.001.

[0038] Figure 4 This is the data chart of VC content detected in Sunshine Rose grapes after 15 days of storage; where ****P<0.0001.

[0039] Figure 5 This is the data chart of total phenolic content detected in Sunshine Rose grapes after 15 days of storage; where ****P<0.0001.

[0040] Figure 6 This is the appearance of bananas during a 6-day storage experiment.

[0041] Figure 7 This is the weight loss data of bananas after 6 days of storage; where ****P<0.0001.

[0042] Figure 8 The pH data of bananas after 6 days of storage are shown in the figure; **P<0.01, ***P<0.001.

[0043] Fig. 9 This is the data graph of VC content detected in bananas after 6 days of storage; where ****P<0.0001.

[0044] Fig.10This is the data graph of total phenolic content detected in bananas after 6 days of storage; where ****P<0.0001. DETAILED DESCRIPTION

[0045] The present invention can be better understood according to the following examples. However, it is easy for those skilled in the art to understand that the contents described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0046] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0047] The weight average molecular weight of the polylactic acid used in the embodiments of the present invention is 60,000 to 80,000, and the weight average molecular weight of the chitosan oligosaccharide is 1,000 to 2,000.

[0048] Example 1: Preparation of Metal-Organic Framework ZIF-8

[0049] Weigh 0.348 g of L-theanine, 0.328 g of eugenol, and 0.273 g of zinc chloride, stir in 40 mL of pure water until dissolved, weigh 1.312 g of 2-methylimidazole, add to the above solution, and stir at room temperature in the dark for 24 hours. After stirring, centrifuge at 10000 r, wash three times with pure water, and freeze-dry to obtain a white solid powder, which is recorded as ZIF-8 complex.

[0050] Example 2: Preparation of blank fiber membrane PLA / CSO

[0051] 1.2 g of polylactic acid and 0.2 g of chitosan oligosaccharide were weighed and dissolved in a mixed solvent of 8 mL of hexafluoroisopropanol and 2 mL of acetic acid to obtain a mixed solution; 6 mL of the mixed solution was transferred into an electrospinning device, and spinning was performed on the electrospinning device at a temperature of 25-30° C., a humidity of 45%-50%, a spinning voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 12 cm, a translation distance of 12 cm, and a drum speed of 1000 r / min to prepare a blank fiber membrane, which was recorded as PLA / CSO.

[0052] Example 3: Metal-organic framework composite fiber film ZIF-8~L-the / Eug 5％ Preparation

[0053] 1.2 g of polylactic acid and 0.2 g of chitosan oligosaccharide were weighed and dissolved in a mixed solvent of 8 mL of hexafluoroisopropanol and 2 mL of acetic acid, and 0.5 g of ZIF-8 complex (prepared in Example 1) was added and mixed to obtain a mixed solution; 6 mL of the mixed solution was transferred into an electrospinning device, and spun on an electrospinning device at a temperature of 25 to 30 ° C, a humidity of 45% to 50%, a spinning voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 12 cm, a translation distance of 12 cm, and a drum speed of 1000 r / min to prepare a metal organic framework composite fiber film, recorded as ZIF-8 ~ L-the / Eug 5％ .

[0054] Example 4: Metal-organic framework composite fiber film ZIF-8~L-the / Eug 10％ Preparation

[0055] 1.2 g of polylactic acid and 0.2 g of chitosan oligosaccharide were weighed and dissolved in a mixed solvent of 8 mL of hexafluoroisopropanol and 2 mL of acetic acid, and 1 g of ZIF-8 complex (prepared in Example 1) was added and mixed to obtain a mixed solution; 6 mL of the mixed solution was transferred into an electrospinning device, and spun on an electrospinning device at a temperature of 25 to 30 ° C, a humidity of 45% to 50%, a spinning voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 12 cm, a translation distance of 12 cm, and a drum speed of 1000 r / min to prepare a metal organic framework composite fiber film, which was recorded as ZIF-8 ~ L-the / Eug 10％ .

[0056] Example 5: Metal-organic framework composite fiber film ZIF-8~L-the / Eug 15％ Preparation

[0057] 1.2 g of polylactic acid and 0.2 g of chitosan oligosaccharide were weighed and dissolved in a mixed solvent of 8 mL of hexafluoroisopropanol and 2 mL of acetic acid, and 1.5 g of ZIF-8 complex (prepared in Example 1) was added and mixed to obtain a mixed solution; 6 mL of the mixed solution was transferred into an electrospinning device, and spun on an electrospinning device at a temperature of 25 to 30 ° C, a humidity of 45% to 50%, a spinning voltage of 15 kV, a flow rate of 0.5 mL / h, a receiving distance of 12 cm, a translation distance of 12 cm, and a drum speed of 1000 r / min to prepare a metal organic framework composite fiber film, which was recorded as ZIF-8 ~ L-the / Eug 15％ .

[0058] Embodiment 6: Method for preserving fiber film

[0059] (1) Select bananas or Sunshine Rose grapes that are uniform in maturity, free of obvious pests and diseases, and have uniform color and firmness;

[0060] (2) The surface of bananas or Sunshine Rose grapes was cleaned and disinfected with 0.2% sodium hypochlorite, and then wrapped with the blank fiber membrane PLA / CSO prepared in Example 2 and stored in a clean, dry and ventilated place. Three samples were tested in parallel.

[0061] (3) The fruit preservation results were evaluated using four indicators: weight loss, pH, VC content, and total phenolic acid (TPC) content.

[0062] Embodiment 7:

[0063] The experimental method of this embodiment is the same as that of embodiment 6, except that the metal organic framework composite fiber film ZIF-8~L-the / Eug prepared in embodiment 3 is used. 5％ Conduct experiments.

[0064] Embodiment 8:

[0065] The experimental method of this embodiment is the same as that of embodiment 6, except that the metal organic framework composite fiber film ZIF-8~L-the / Eug prepared in embodiment 4 is used. 10％ Conduct experiments.

[0066] Embodiment 9:

[0067] The experimental method of this embodiment is the same as that of embodiment 6, except that the metal organic framework composite fiber film ZIF-8~L-the / Eug prepared in embodiment 5 is used. 15％ Conduct experiments.

[0068] Embodiment 10:

[0069] The experiments of Examples 6 to 9 were conducted to evaluate the fruit preservation results using four indicators: weight loss, pH, VC content, and total phenol (TPC) content.

[0070] (i) During the storage of fruits, the weight loss rate is the most intuitive indicator of the freshness of fruits. (ii) Organic acids are continuously consumed as respiratory substrates, resulting in an increase in pH. Microbial metabolism can also lead to an increase in environmental pH. (iii) VC can delay cell aging due to oxidation. Due to the action of ascorbic acid oxidase, VC will undergo enzymatic oxidation in the presence of O2, resulting in VC degradation. (iv) Phenolic substances are used to evaluate the antioxidant properties of fruits.

[0071] Therefore, the weight loss rate and pH value of the fruits during storage were monitored, and the changes in VC content in the fruits were evaluated by drawing a VC standard curve based on 4% metaphosphoric acid, and the TPC content in the fruits was determined based on the gallic acid standard curve.

[0072] (1) Figure 1 to Figure 5As shown in the results, in the 15-day storage experiment of Sunshine Rose grapes, the results of various indicators of the PLA / CSO group were significantly worse than those of the metal organic framework composite fiber film group. 15％ The average weight loss rate of the group was only 3.3% (with a very significant difference), the pH value remained at 6.9 (with a significant difference), which was slightly different from the actual change (the pH of fresh Sunshine Rose grapes was about 6.6), and the VC and total phenol content were much higher than those of the other groups (with a very significant difference), indicating that the fiber membrane ZIF-8-L-the / Eug 15％ It can greatly maintain the freshness of Sunshine Rose.

[0073] (2) Figure 6 to Figure 10 As shown, in a 6-day storage experiment of bananas, the preservation performance of the fiber membrane on bananas was tested. Similarly, the ZIF-8-L-the / Eug 15％ The group showed superiority in the 6-day banana preservation experiment, with an average weight loss rate of only 2.5% (with a very significant difference), pH maintained at 6.6 (with a significant difference, the pH of fresh bananas is about 6.4), and VC and total phenol content significantly higher than those of the other groups (with a very significant difference).

[0074] The present invention provides a metal organic framework composite fiber film designed based on an electrospinning process, a preparation method thereof, and a method for its application in preservation. There are many methods and approaches to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. All components not specified in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a metal organic framework composite fiber film based on an electrospinning process, characterized in that: The steps include: (1) mixing theanine, eugenol, zinc salt, 2-methylimidazole, and a first solvent, and then centrifuging, washing, and drying to obtain a metal organic framework complex; (2) mixing polylactic acid, chitosan oligosaccharide and a second solvent, and then adding the metal organic framework complex prepared in step (1) to mix, to obtain a mixed solution; and electrospinning the mixed solution to obtain a metal organic framework composite fiber film.

2. The preparation method according to claim 1, characterized in that: The zinc salt is any one of zinc chloride and zinc acetate or a combination of the two; the first solvent is any one of water and methanol or a combination of the two; the second solvent is a mixture of hexafluoroisopropanol and acetic acid in any proportion.

3. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of theanine to eugenol, zinc salt and 2-methylimidazole is 1-2:1-2:1-2:6-8.

4. The preparation method according to claim 1, characterized in that: In step (1), the mixing is stirred at room temperature in the dark for 20 to 30 hours.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of the polylactic acid to the chitosan oligosaccharide is 1.0-1.5:0.1-0.4; the mass volume ratio of the polylactic acid to the second solvent is 1.0-1.5 g:8-12 mL.

6. The preparation method according to claim 1, characterized in that: In step (2), the concentration of the metal organic framework complex in the mixed solution is 4% to 16% g / mL.

7. The preparation method according to claim 1, characterized in that: In step (2), the electrospinning parameters are: receiving distance of 8 to 12 cm, spinning voltage of 14 to 16 kV, ambient humidity of 45% to 50%, and temperature of 20 to 30°C.

8. The metal organic framework composite fiber film prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the metal organic framework composite fiber film according to claim 8 in the preparation of food preservative film.

10. The use according to claim 9, characterized in that: The food is vegetables and / or fruits.

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