Food packaging film loaded with metal organic framework and erythritol and preparation method of food packaging film

Abstract

The invention relates to the technical field of food packaging films, and discloses a food packaging film loaded with a metal organic framework and erythritol and a preparation method thereof, and the preparation method comprises the following steps: (1) mixing erythritol and HP [beta] CD in water, and carrying out ultrasonic treatment and freeze-drying to obtain an inclusion compound; (2) mixing a polymer, gelatin and glycerol in a solvent to obtain a primary spinning solution; (3) mixing the clathrate compound and ZIF-8 in the primary spinning solution to obtain a final spinning solution; and (4) carrying out electrostatic spinning on the final spinning solution to obtain the food packaging film. The food preservative film prepared by the invention has an inhibition effect on staphylococcus aureus and escherichia coli, and can effectively prolong the shelf life of fruits.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging films, in particular to a food packaging film loaded with a metal organic framework and erythritol and a preparation method thereof. Background Art

[0002] Electrospinning is a relatively common technology for preparing ultrafine one-dimensional nanofibers, two-dimensional nonwoven membranes and three-dimensional scaffolds. It can be used to prepare nano / micro fibers with large surface area / volume ratio, controllable size, high load, light weight, excellent adjustability and wide flexibility. Electrospinning technology is versatile, low-cost and convenient. Antimicrobial agents of different properties can be encapsulated inside or on the surface of nanofibers to better maintain the antibacterial activity of the antimicrobial agents. The antibacterial nanofilms prepared by it can be used to improve the quality and safety of food.

[0003] Metal-organic frameworks (MOFs) are formed by linking metal ions with organic ligand clusters through coordination bonds. MOFs exhibit beneficial properties such as high surface area, controllable pore size, functional flexibility, easy modification, and good biocompatibility. ZIF-8 (Zn-MOF) is a subclass of MOFs, which is composed of zinc and 2-methylimidazole as the metal ion core and ligand, respectively. Zn-MOFs can be used as multifunctional materials in the packaging field due to their antibacterial / antioxidant efficacy, high porosity, UV absorption, and good dispersibility in aqueous media.

[0004] Erythritol is a four-carbon sugar alcohol, mainly derived from natural plants. It is widely used as a food additive and has multiple active effects. Erythritol is a powerful antioxidant that can effectively remove free radicals, prevent food oxidation and extend the shelf life. It has important research value for protecting food nutrients and improving food safety. At the same time, due to the advantages of natural sources, compared with chemically synthesized antioxidants, it not only has antioxidant effects, but also has the characteristics of safety, health and environmental protection, so it has broader application prospects in the food industry. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a food packaging film loaded with a metal organic framework and erythritol and a preparation method thereof in view of the deficiencies in the prior art. The antibacterial active substances are encapsulated by electrospinning technology, which can retain the antibacterial active substances in the food packaging film and play a role in sustained release of the active substances.

[0006] In order to solve the above technical problems, the present invention discloses a food packaging film loaded with a metal organic framework and erythritol and a preparation method thereof. In the preparation method of the present invention, erythritol containing antioxidants is encapsulated in a cavity carrier to form an inclusion complex, which is loaded onto a nanofiber membrane together with a metal organic framework. The fiber membrane can effectively prolong the stability of the antioxidant while retaining the antibacterial properties of the metal organic framework and provide a sustained release of the antioxidant, thereby improving the bioavailability and extending the shelf life of the food. Considering that the simple addition of erythritol is not conducive to its long-term stability and efficient utilization, the present invention uses HPβCD as a cavity encapsulation carrier and forms an inclusion complex through ultrasound-mediated assembly.

[0007] The specific technical solutions are as follows:

[0008] A method for preparing a food packaging film comprises the following steps:

[0009] (1) mixing erythritol and hydroxypropyl-β-cyclodextrin in water, ultrasonically treating, and freeze-drying to obtain an inclusion compound;

[0010] (2) mixing the polymer, gelatin and glycerol in a solvent to obtain a primary spinning solution;

[0011] (3) mixing the inclusion compound and ZIF-8 into the primary spinning solution to obtain a final spinning solution;

[0012] (4) electrospinning the final spinning solution to obtain a food packaging film.

[0013] Wherein, in step (1), the molar ratio of erythritol to hydroxypropyl-β-cyclodextrin (HPβCD) is 1:1; the ultrasonic treatment has an ultrasonic power of 60-80w, a pulse interval of 1s, and an ultrasonic time of 2-4h. Preferably, the ultrasonic treatment has an ultrasonic power of 65w, a pulse interval of 1s, and an ultrasonic time of 2h. Preferably, the concentration of erythritol in water is 125mmol / L.

[0014] Wherein, in step (2), the polymer is polylactic acid and / or polycaprolactone; preferably polylactic acid (PLA); more preferably, the weight average molecular weight (Mw) of polylactic acid is 118000Da. Since the spinnability of bioactive substances is limited, adding appropriate biodegradable and biocompatible polymers can improve the spinnability of the solution for use as a spinning substrate.

[0015] Wherein, in step (2), the solvent is hexafluoroisopropanol (HFIP) and / or acetic acid, preferably a combination of hexafluoroisopropanol and acetic acid, and more preferably, the volume ratio of hexafluoroisopropanol to acetic acid is 4:1.

[0016] Wherein, in step (2), in the primary spinning solution, the mass concentration of gelatin is 2% to 5%, and the mass ratio of polymer, gelatin and glycerol is 14:2:3. Preferably, the mass concentration of gelatin is 2%. The concentration of the spinning material in the spinning solution is a factor that affects the electrospinning effect.

[0017] Wherein, in step (3), the mass concentration of the inclusion compound in the final spinning solution is 5% to 15%, and the mass ratio of the inclusion compound to ZIF-8 is 1:1.

[0018] Preferably, in step (3), the ZIF-8 is prepared by the following method: adding ZnCl2 and 2-methylimidazole to methanol, stirring overnight in the dark, centrifuging and washing, and drying to obtain the metal organic framework ZIF-8. The molar ratio of ZnCl2 to 2-methylimidazole is 1:4.

[0019] Wherein, in step (4), the electrospinning has a propulsion rate of 0.4-0.5 mL / h and a voltage of 15-18 kV. Preferably, the propulsion rate is 0.4 mL / h and the voltage is 16 kV.

[0020] In a second aspect, the present invention provides a food packaging film prepared by the preparation method described in the first aspect.

[0021] In a third aspect, the present invention provides the use of the food packaging film described in the second aspect in the antibacterial and fresh-keeping of fruits. Preferably, the fruit is grapes, and the antibacterial is the inhibition of Staphylococcus aureus and Escherichia coli.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention prepares a metal organic framework and erythritol inclusion complex and loads it into an electrospun membrane, so that the prepared food packaging film not only retains the antibacterial property of the metal organic framework, but also effectively prolongs the antioxidant property and stability of erythritol.

[0024] (2) The present invention uses HPβCD to encapsulate erythritol to form an inclusion compound, which has better antioxidant capacity, and prepares a nano electrospinning multifunctional food preservative film through electrospinning technology. The nanospinning fiber film made of cyclodextrin as a non-polymer carrier has not only higher porosity and specific surface area, but also biocompatibility, and has high application value in food packaging.

[0025] (3) The food packaging film prepared by the present invention has simple processing and storage processes and low production costs. It effectively prolongs the shelf life of the product while not affecting the taste of the food, and is in line with the modern concept of healthy, environmentally friendly and nutritious food production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 This is a scanning electron microscope image of the fiber membrane prepared by the present invention. Figure 1 a is Ery, Figure 1 b is HPβCD, Figure 1 c is HPβCD / Ery inclusion complex, Figure 1 d is ZIF-8, Figure 1 e is PLA / Gel / GI, Figure 1 f is ZIF-8~HPβCD / Ery 5％ , Figure 1 g is ZIF-8~HPβCD / Ery 10％ , Figure 1 h is ZIF-8~HPβCD / Ery 15％ .

[0028] Figure 2 is a diameter diagram of the fiber membrane prepared by the present invention, Figure 2 a is PLA / Gel / GI film, Figure 2 b is ZIF-8~HPβCD / Ery 5％ membrane, Figure 2 c is ZIF-8~HPβCD / Ery 10％ membrane, Figure 2 d is ZIF-8~HPβCD / Ery 15％ membrane.

[0029] Figure 3 This is a graph showing the test results of the mechanical properties of the fiber membrane obtained in the present invention.

[0030] Figure 4 This is a graph showing the experimental results of applying the fiber membrane obtained in the present invention to the preservation of grapes for 12 days.

[0031] Figure 5 This is a graph showing the antibacterial test of the fiber membrane obtained in the present invention.

[0032] Figure 6 This is a graph showing the antioxidant capacity of the fiber membrane obtained in the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose and technical solution of the present invention clearer, the following specific examples are used to explain in detail, but are not limited to these specific examples. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0034] Example 1

[0035] The preparation method of food packaging film comprises the following steps:

[0036] (1) Dissolve 5 mmol of erythritol (Ery) and 5 mmol of hydroxypropyl-β-cyclodextrin (HPβCD) in 40 mL of pure water, treat the solution with an ultrasonic cell disruptor at a power of 65 W, a pulse interval of 1 s, and a time of 2 h, and freeze-dry to obtain a white solid clot, i.e., the inclusion complex.

[0037] (2) Add 2 mol ZnCl2 and 8 mol 2-methylimidazole to 40 mL methanol, stir overnight in the dark, centrifuge at 10,000 r / min for 10 min, wash three times with ethanol, and dry to obtain a white powder, namely ZIF-8.

[0038] (3) 1.4 g of polylactic acid (PLA, Mw = 118000 Da), 0.2 g of gelatin (Gel) and 0.3 g of glycerol (GI) were dissolved in 8 mL of hexafluoroisopropanol (HFIP) and 2 mL of acetic acid and stirred for 8 h to obtain a preliminary spinning solution. Inclusion complex and ZIF-8 (inclusion complex: ZIF-8 = 1:1, m / m) with a mass concentration of 5%, 10% and 15% were added to the preliminary spinning solution, respectively, and stirred for 6 h to obtain a final spinning solution. The fiber membrane ZIF-8~HPβCD / Ery was prepared by electrospinning equipment at a flow rate of 0.4 mL / h and a voltage of 16 kV. 5％ 、ZIF-8~HPβCD / Ery 10％ 、ZIF-8~HPβCD / Ery 15％ , wherein the superscripts 5%, 10% and 15% respectively represent the mass concentration of the inclusion complex added to the spinning solution in step (3).

[0039] The fiber membrane PLA / Gel / GI without inclusion complex and ZIF-8 was prepared according to the above preparation method: 1.4 g PLA, 0.2 g Gel and 0.3 g GI were dissolved in 8 mL HFIP and 2 mL acetic acid and stirred for 8 h to obtain the spinning solution, which was prepared by electrospinning equipment at a flow rate of 0.4 mL / h and a voltage of 16 kV.

[0040] According to the above preparation method, PLA / Gel / GI-ZIF-8 fiber membrane without inclusion compound was prepared. 5％ 、PLA / Gel / GI~ZIF-8 10％ 、PLA / Gel / GI~ZIF-8 15％1.4 g PLA, 0.2 g Gel and 0.3 g GI were dissolved in 8 mL HFIP and 2 mL acetic acid and stirred for 8 h to obtain a spinning solution. 5%, 10% and 15% ZIF-8 (prepared according to the above step (2)) were added to the spinning solution respectively and stirred for 6 h. A series of fiber membranes were prepared by electrospinning at a flow rate of 0.4 mL / h and a voltage of 16 kV.

[0041] Example 2

[0042] The performance test of the food packaging film loaded with metal organic framework and erythritol prepared by the sample of the present invention is carried out as follows:

[0043] 1. SEM test

[0044] Ery, HPβCD, inclusion complex, ZIF-8 and nanofiber membranes were observed by scanning electron microscopy. Gold was sprayed on different fiber membranes, and then their morphologies were captured by scanning electron microscopy at an accelerating voltage of 120 kV and a magnification of 1000 times at randomly selected sample positions.

[0045] The results show that if Figure 1 As shown in Figure 2, compared with the PLA / Gel / GI membrane, the fiber diameter increased significantly with the increase of ZIF-8~HPβCD / Ery concentration. The specific data are as follows: Figure 2 As shown in Figure 2, the fiber diameter increased from 337.36 nm of PLA / Gel / GI to 393.37 nm (ZIF-8~HPβCD / Ery 5％ ), 1023.58nm (ZIF-8~HPβCD / Ery 10％ ) and 2184.20nm (ZIF-8~HPβCD / Ery 15％ ).

[0046] As for the nanofilm PLA / Gel / GI~ZIF-8 without inclusion complex, with the increase of ZIF-8 addition, the nanofiber membrane has an irregular surface and the fiber diameter increases due to the successful embedding of ZIF-8. 5％ 、PLA / Gel / GI~ZIF-8 10％ 、PLA / Gel / GI~ZIF-8 15％ The fiber diameters are 297.53, 445.78, 674.38, and 798.45 nm, respectively.

[0047] 2. Mechanical properties test

[0048] The mechanical properties of the fiber membrane were measured by a universal testing machine (ZWICK) with a load of 10 N and a force rate of 1 mm min-1 , the temperature is 27℃, the stress-strain curve is as follows Figure 3 shown.

[0049] The results showed that compared with the fiber membrane PLA / Gel / GI, with the increase of the addition amount of ZIF-8~HPβCD / Ery, the elongation at break of the fiber membrane decreased from 83.37% to 51.55%, 30.07% and 27.51% respectively ( Figure 3 ), the elastic modulus decreased from 46.24MPa to 43.15MPa, 36.19MPa and 30.06MPa respectively ( Figure 3 ), the tensile strength decreased from 3.57MPa to 2.41MPa, 1.53MPa and 1.51MPa respectively ( Figure 3 ), indicating that the mechanical properties were impaired. 5％ The nanofiber membrane has the best mechanical properties.

[0050] However, for the nanofilm PLA / Gel / GI~ZIF-8 without inclusion complex, as the amount of ZIF-8 added increased, the elongation at break, elastic modulus and tensile strength of PLA / Gel / GI~ZIF-8 nanofiber membrane decreased. 5％ The PLA / Gel / GI membrane had an elongation at break of 43.22%, an elastic modulus of 41.89 MPa, and a tensile strength of 4.17 MPa. The mechanical properties of the nanofiber membrane with HPβCD / Ery and ZIF-8 were better than those of the membrane with only ZIF-8.

[0051] 3. Food preservation test

[0052] Insert a sterile needle into the center of the grape with a diameter of 1 mm and a depth of 5 mm, then inject 3 μL of a concentration of 10 CFU mL -1 The gray mold suspension (inoculate gray mold on Sabouraud agar plate and culture until rich spores are produced, use an inoculation loop to directly pick a ring of spores into the diluent, and then use the ten-fold dilution method to make a suitable concentration of bacterial suspension) is inoculated on the wound. According to the size and shape of the grapes, the nanofiber membranes of different concentrations are cut into appropriate sizes. Gently wrap the cut nanofiber membrane on the surface of the grapes, use an appropriate amount of water to assist the membrane to fit, and place the inoculated grapes in an incubator at 27°C for 12 days. The experimental data comes from three replicates, each of which contains three grapes.

[0053] The results show that if Figure 4 As shown, the food wrap loaded with metal-organic frameworks and erythritol can keep the grapes in good condition for a long time, delay the shrinkage and rot of the grapes, and maintain their freshness.

[0054] For PLA / Gel / GI membrane without inclusion compound, after adding only different concentrations of ZIF-8 (i.e. PLA / Gel / GI~ZIF-8 membrane), the freshness of grapes can still be maintained. The more ZIF-8 is added, the better the freshness of grapes is maintained. However, the overall level is not as good as the effect of ZIF-8~HPβCD / Ery membrane with HPβCD / Ery inclusion compound added. The experimental grapes in the PLA / Gel / GI~ZIF-8 membrane group were more shrunken and wrinkled, with more wounds and rot, and the weight loss rate also increased. PLA / Gel / GI, ZIF-8~HPβCD / Ery 5％ 、ZIF-8~HPβCD / Ery 10％ and ZIF-8~HPβCD / Ery 15％ The weight loss rates of the experimental grapes were 67.58%, 34.23%, 27.67% and 6.43% respectively, while PLA / Gel / GI~ZIF-8 5％ 、PLA / Gel / GI~ZIF-8 10％ and PLA / Gel / GI~ZIF-8 15％ The weight loss rates of the experimental grapes were 44.78%, 37.33% and 29.89% respectively.

[0055] 4. Inhibition zone test

[0056] Escherichia coli and Staphylococcus aureus were placed in conical flasks containing LB liquid medium, and cultured overnight on a shaker for activation. The bacterial solution was diluted, and 1 mL of the bacterial solution was pipetted into a sterile test tube on a sterile operating table, and 9 mL of sterile water was added to mix evenly to form 10 -1 Dilution. Take 70μL of dilution and evenly spread it on the surface of sterilized solid culture medium. The nanofiber membrane with a diameter of 10mm is precisely placed in the middle of the culture medium. The solid culture medium is cultured in a constant temperature incubator at 37℃ for 12h. The diameter of the inhibition zone of the nanofiber membrane is observed and measured in two different bacterial culture media.

[0057] The results show that if Figure 5 As shown in the figure, PLA / Gel / GI membrane has almost no antibacterial effect on Escherichia coli, while ZIF-8~HPβCD / Ery 5％ 、ZIF-8~HPβCD / Ery 10％ 、ZIF-8~HPβCD / Ery 15％The antibacterial diameters of the nanofiber membrane against Escherichia coli were 10.48, 11.79 and 12.93 mm respectively. The PLA / Gel / GI membrane had a slight inhibitory effect on Staphylococcus aureus, showing a smaller inhibition zone. After adding 5%, 10% and 15% of the inclusion complex, the inhibition zone diameter of ZIF-8~HPβCD / Ery increased. The results showed that the inclusion complex retained the antibacterial activity of ZIF-8 and had a good application prospect in fruit preservation materials.

[0058] The inhibitory effects of PLA / Gel / GI-ZIF-8 membrane without inclusion complex and membrane with HPβCD / Ery on Escherichia coli and Staphylococcus aureus were similar.

[0059] 5. Antioxidant capacity test

[0060] First, 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) was prepared with ethanol to obtain a 1mmol / L DPPH solution. 5mg of the fiber membrane was placed in a 5mL centrifuge tube. Then, 3mL of the DPPH solution was pipetted into the centrifuge tube with a pipette. The tube was sealed and placed in the dark for 30 minutes. The absorbance was measured at a wavelength of 517nm. The free radical scavenging rate of the solution was calculated by the following formula:

[0061]

[0062] A0 represents the absorbance of PLA / Gel / GI membrane, and A1 represents the absorbance of different concentrations of ZIF-8~HPβCD / Ery.

[0063] The results show that if Figure 6 As shown in Figure 2, the scavenging rate of DPPH by PLA / Gel / GI membrane was 14.9±3.4%, and that of ZIF-8~HPβCD / Ery 5％ 、ZIF-8~HPβCD / Ery 10％ and ZIF-8~HPβCD / Ery 15％ The scavenging rates of DPPH were 40.8±6.37%, 56.9±6.60% and 83.1±9.11% respectively. 5％ 、PLA / Gel / GI~ZIF-8 10％ and PLA / Gel / GI~ZIF-8 15％ The scavenging rates of DPPH were 21.8±5.76%, 30.9±5.97% and 43.7±7.13%, respectively. The scavenging ability of PLA / Gel / GI membrane without HPβCD / Ery for DPPH free radicals was significantly lower than that of PLA / Gel / GI membrane with HPβCD / Ery.

[0064] The present invention provides a food packaging film loaded with metal organic framework and erythritol and a method for preparing the same. 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 principle 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 by existing technologies.

Claims

1. A method for preparing a food packaging film, characterized in that: The steps include: (1) mixing erythritol and hydroxypropyl-β-cyclodextrin in water, ultrasonically treating, and freeze-drying to obtain an inclusion compound; (2) mixing the polymer, gelatin and glycerol in a solvent to obtain a primary spinning solution; (3) mixing the inclusion compound and ZIF-8 into the primary spinning solution to obtain a final spinning solution; (4) electrospinning the final spinning solution to obtain a food packaging film.

2. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of erythritol to hydroxypropyl-β-cyclodextrin is 1:1; and in the ultrasonic treatment, the ultrasonic power is 60-80w, the pulse interval is 1s, and the ultrasonic time is 2-4h.

3. The preparation method according to claim 1, characterized in that: In step (2), the polymer is polylactic acid and / or polycaprolactone; preferably polylactic acid.

4. The preparation method according to claim 1, characterized in that: In step (2), the solvent is hexafluoroisopropanol and / or acetic acid.

5. The preparation method according to claim 1, characterized in that: In step (2), in the primary spinning solution, the mass concentration of gelatin is 2% to 5%, and the mass ratio of polymer, gelatin and glycerol is 14:2:

3.

6. The preparation method according to claim 1, characterized in that: In step (3), the mass concentration of the inclusion compound in the final spinning solution is 5% to 15%.

7. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of the inclusion complex to ZIF-8 is 1:

1.

8. The preparation method according to claim 1, characterized in that: In step (4), the electrospinning has a propulsion rate of 0.4-0.5 mL / h and a voltage of 15-18 kV.

9. A food packaging film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the food packaging film according to claim 9 in the antibacterial and fresh-keeping of fruits.

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