Cellulose nanocrystal-containing nanofiber membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of packaging films, and particularly relates to a nanofiber film containing cellulose nanocrystals as well as a preparation method and application of the nanofiber film. The preparation method comprises the following specific steps: dissolving zein, polyethylene oxide and cellulose nanocrystals in an acetic acid solution, uniformly mixing, and adding oregano essential oil to obtain a spinning solution; and carrying out electrostatic spinning on the spinning solution to obtain the nanofiber membrane containing the cellulose nanocrystals. In the prepared nanofiber membrane, the cellulose nanocrystals from passion fruit peel can effectively improve the mechanical property and barrier property of the OZP electrostatic spinning nanofiber membrane, have the effects of delaying deterioration of pork and prolonging the shelf life of the pork, and have great application potential in meat packaging.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging films, and in particular relates to a nanofiber film containing cellulose nanocrystals and a preparation method and application thereof. Background Art

[0002] Essential oil is a substance extracted from plants with a variety of biologically active functions such as antioxidant, antibacterial, and antiviral. Among them, oregano essential oil stands out due to its sophisticated extraction process, high purity of finished products, and strong antibacterial activity. However, since essential oils are volatile and unstable, they are easily degraded by oxidation, heat, and light and lose their activity, which limits their application in food preservation. However, encapsulation has been proven to be an effective way to solve this problem. Electrospinning is a new encapsulation technology that can be used to prepare nanofiber membranes. Compared with ordinary fiber membranes, nanofiber membranes have high porosity, high specific surface area, and ultrafine structure, so they have better physical properties, and can also achieve good embedding and loading of sensitive and volatile substances without involving high temperatures, thereby preparing antibacterial food packaging to extend the shelf life of food.

[0003] However, electrospinning technology has high requirements for materials and requires a certain degree of spinnability. Only when the spinning solution reaches a certain chain entanglement concentration can the polymer be effectively stretched and form a jet under the action of the electric field force. Zein has good film-forming properties. At the same time, compared with other proteins, it is more hydrophobic. Because of the presence of a large number of non-polar amino acid residues, such as proline, leucine, and alanine, it is an ideal material that is widely used in electrospinning. In addition, polyethylene oxide (PEO) is a polymer with a large molecular weight that can increase the chain entanglement concentration of the solution and thus improve its spinnability. It has been used as a spinning aid in many studies.

[0004] In the prior art, nanofiber membranes prepared by essential oils and Zein mostly focus on the antibacterial properties of the membranes and ignore the mechanical properties and barrier properties of the membranes. However, antibacterial nanofiber membranes need to have good mechanical properties and barrier properties to meet the needs of practical applications.

[0005] Therefore, it is of great significance to develop a new nanofibrous membrane containing cellulose nanocrystals. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method of encapsulating oregano essential oil in a zein / polyethylene oxide (OZP) nanofiber membrane using electrospinning technology in view of the deficiencies of the prior art. More importantly, the present invention will creatively explore the role of cellulose nanocrystals (CNC) derived from passion fruit peel as a reinforcing material in the active nanofiber membrane, conduct a comprehensive analysis of the morphology, mechanical properties, water vapor permeability, crystallinity, etc. of the fiber membrane, and apply the fiber membrane with the optimal CNC addition amount to the storage of fresh pork to verify its antibacterial activity and practical applicability.

[0007] In order to solve the above technical problems, the present invention discloses a method for preparing a nanofiber membrane containing cellulose nanocrystals, the specific steps of which are: dissolving zein, polyethylene oxide and cellulose nanocrystals in an acetic acid solution, mixing them evenly, and adding oregano essential oil to obtain a spinning solution; and electrospinning the spinning solution to obtain a nanofiber membrane containing cellulose nanocrystals.

[0008] Specifically, the mass ratio of zein to polyethylene oxide is 99:1.

[0009] Specifically, the added amount of the cellulose nanocrystals is 1.5-6% of the total mass of zein and polyethylene oxide; preferably, the added amount of the cellulose nanocrystals is 3% of the total mass of zein and polyethylene oxide.

[0010] Specifically, the source of the cellulose nanocrystals is purple passion fruit peel.

[0011] Specifically, the concentration of the acetic acid solution is 70% v / v; the mass volume ratio of the total mass of the zein and polyethylene oxide to the acetic acid solution is 1 g:5 ml.

[0012] Specifically, the amount of oregano essential oil added is 50% to 60% of the total mass of zein and polyethylene oxide; preferably, the amount of oregano essential oil added is 50% of the total mass of zein and polyethylene oxide.

[0013] Furthermore, the nanofiber membrane containing cellulose nanocrystals prepared by the above preparation method is also within the protection scope of the present invention.

[0014] Furthermore, the use of the nanofiber membrane containing cellulose nanocrystals prepared by the above preparation method in the preparation of packaging for delaying meat deterioration is also within the scope of protection of the present invention;

[0015] Preferably, the application is the use of a nanofiber membrane containing cellulose nanocrystals in the preparation of packaging for delaying spoilage of pork.

[0016] Specifically, in some embodiments of the present invention, the micromorphology, tensile strength, elongation at break and water vapor permeability of the prepared nanofiber membrane containing cellulose nanocrystals were tested, which proved that the nanofiber membrane had good mechanical properties and barrier properties. Furthermore, through the study of the effect of the nanofiber membrane on the shelf life of fresh pork, it was found that the 3% CNC-ZP membrane prepared by the present invention was used for pork preservation, which could extend the shelf life of pork by about 2 days when stored at 4 degrees, which proved the application prospect of the above-mentioned nanofiber membrane containing cellulose nanocrystals in packaging for delaying meat deterioration.

[0017] Beneficial effects: In the nanofiber membrane prepared by the present invention, the cellulose nanocrystals derived from passion fruit peel can effectively improve the mechanical properties and barrier properties of the OZP electrospun nanofiber membrane, and have the effect of delaying the deterioration of pork and extending the shelf life of pork, and has great application potential in meat packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 The SEM images and fiber diameter distribution of the electrospun nanofiber membranes with different CNC contents added in the embodiments of the present invention, wherein A is 0% C-OZP, B is 1.5% C-OZP, C is 3% C-OZP, D is 4.5% C-OZP, and E is 6% C-OZP;

[0020] Figure 2 XRD patterns of electrospun nanofiber membranes with different CNC contents added in the embodiments of the present invention;

[0021] Figure 3 The TVC curves of pork in different treatment groups during storage in the embodiment of the present invention are shown;

[0022] Figure 4 1 is a curve showing the change of TVB-N of pork in different treatment groups during storage in the embodiment of the present invention. DETAILED DESCRIPTION

[0023] 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.

[0024] In the following examples, Zein was purchased from Sigma-Aldrich (Z3625-500G), and PEO was purchased from Shanghai Yuanye Biotechnology Co., Ltd. (S59089-100g);

[0025] In the following examples, CNC is derived from passion fruit peel, and the preparation steps are as follows:

[0026] Cellulose extraction: Take the passion fruit peel without the contents, soak it in water, wash it, cut it into small pieces, and dry it in an oven at 65°C for 48 hours. Grind the dried peel with a grinder and pass it through a 100-mesh sieve to obtain passion fruit peel powder (PP). The passion fruit peel powder is placed in 80°C water at a ratio of 1:20 (w / v) and heated to extract water-soluble substances such as pectin in PP, filtered and dried at 65°C; the dried powder is mixed with 10% (w / v) sodium hydroxide solution at a ratio of 1:10 (w / v), and water-bathed at 80°C for 4 hours to remove impurities such as lignin and hemicellulose in PP, filtered and washed 4 to 5 times and dried at 65°C; the dried powder is taken again, mixed with 7.5% (w / v) sodium chlorite solution (adjusted to pH to about 4.5 with glacial acetic acid), and water-bathed at 75°C for 3 hours to achieve the effect of bleaching the powder and removing impurities such as residual lignin and hemicellulose, then filtered and washed to a neutral pH value, and dried at 65°C to obtain pure cellulose powder (PPC). The yield of this step is 17.03%±0.66%.

[0027] Preparation of CNC by sulfuric acid hydrolysis: PPC was placed in a 61% (w / w) sulfuric acid solution at a ratio of 1:20 (w / v) in a 55°C water bath for 2 hours. After the reaction time was up, 10 times 4°C condensed water was added to terminate the reaction, and the excess sulfuric acid was removed by centrifugation at 4°C 1000×g for 20 minutes. The powder precipitate was placed in a 6000-8000Da dialysis bag and dialyzed for 3 days to remove the remaining small molecule impurities. The liquid in the dialysis bag was collected and centrifuged again at 4°C 1000×g for 15 minutes to obtain the supernatant, and CNC was obtained after freeze-drying for 48 hours.

[0028] The bacterial cellulose in the following examples was purchased from Hainan Yide Food Co., Ltd. and the standard was food grade;

[0029] The nanocellulose fibers in the following examples were purchased from Zhejiang Jinjiahao Green Nanomaterials Co., Ltd., cellulose nanofibrils (CNF, length 100-5000 nm, width 1-20 nm, mass fraction 0.5%-5%).

[0030] Example 1: Preparation of Nanofiber Membrane (Containing Cellulose Nanocrystals)

[0031] 1.98 g of zein, 0.02 g of polyethylene oxide (PEO) and cellulose nanocrystals (CNC) were weighed separately and dissolved in 10 ml of 70% (v / v) acetic acid solution (solvent: water) and stirred overnight. After all the solution was dissolved, 1 g of oregano essential oil was added and stirred at room temperature for 30 min to obtain a spinning solution, wherein the amount of CNC added was 0%, 1.5%, 3%, 4.5% and 6% (w / w, relative to the total amount of Zein and PEO), respectively.

[0032] Using DP30 electrospinning instrument (Yunfan, China), spinning was carried out under the conditions of flow rate 0.0012 mm / s, voltage 15-16 kV, temperature 25±5°C, humidity 40-50%, and needle distance 15 cm from the receiving plate. The obtained fiber membrane samples were named 0% C-OZP, 1.5% C-OZP, 3% C-OZP, 4.5% C-OZP, and 6% C-OZP according to the amount of CNC added. The pure Zein / PEO membrane without adding essential oil and CNC was named ZP.

[0033] Example 2: Preparation of nanofiber membrane (containing bacterial cellulose or nanocellulose fibers)

[0034] The preparation method in this embodiment is the same as above, except that the added CNC is replaced by 3% added bacterial cellulose and 3% added nanocellulose fiber, respectively, to obtain a bacterial cellulose film and a nanocellulose fiber film.

[0035] Example 3: Characterization of Nanofiber Membrane Properties

[0036] 3.1 Scanning electron microscopy: The fiber morphology of the samples was photographed using a Regulus 8230 scanning electron microscope (Hitachi, Japan). The diameters of at least 100 nanofibers were analyzed using Nano Measurer 1.2.

[0037] Figure 1 SEM images and fiber diameter distribution of electrospun nanofiber membranes with different CNC additions, where A is 0% C-OZP, B is 1.5% C-OZP, C is 3% C-OZP, D is 4.5% C-OZP, and E is 6% C-OZP; the fibers in the figure are cylindrical, uniform and smooth. As the CNC addition amount increases from 0% to 6%, the average fiber diameter increases from 321.12nm to 433.03nm. This is mainly because the viscosity of the polymer solution becomes higher under the action of CNC. This indicates that the higher the degree of entanglement of the polymer chains, the greater the resistance of the solution to the tensile force generated by the charge on the jet, and the fiber size will increase.

[0038] 3.2 Mechanical properties: The fiber membrane was cut into 1 cm × 10 cm pieces and subjected to tensile testing using a TA-XT plus texture analyzer (SMS, UK) and a Tensile Grips probe, with the probe height set to 50 mm and the speed to 5 mm / s.

[0039] Table 1 shows the mechanical properties of nanofiber membranes with different CNC addition amounts and films with 3% nanocellulose fibers. It can be seen from Table 1 that when the CNC addition amount is 1.5% to 4.5%, the tensile strength of the fiber membrane is significantly enhanced compared with the 0% group (p<0.05); but when the CNC addition amount is increased to 6%, the tensile strength of the fiber membrane is reduced. It can be concluded that due to the formation of a dense CNC network, the tensile strength of the material will indeed be significantly improved; but too high a CNC content will also reduce the interaction between CNC and the fiber membrane matrix, resulting in a decrease in the tensile strength of the fiber membrane.

[0040] Table 1 also records the elongation at break of the fiber membrane. It can be found that the elongation at break of the group with CNC addition is significantly lower than that of the 0% group (p<0.05), which indicates that the addition of CNC reduces the elongation at break of the fiber membrane, that is, reduces the tensile properties of the fiber membrane. This is mainly because the combination of CNC and the fiber membrane matrix restricts the chain movement of the polymer.

[0041] In addition, compared with the film with bacterial cellulose (3%) added, under the same addition ratio, the 3% C-OZP film has higher tensile strength and elongation at break. It can be seen that passion fruit peel CNC has a better improvement in the mechanical properties of the film than bacterial cellulose.

[0042] Table 1 Mechanical properties of nanofiber membranes with different CNC addition amounts and films with 3% bacterial cellulose addition

[0043]

[0044] Note: The averages with different superscripts (ad) are significantly different (p<0.05, n=3)

[0045] 3.3 Water vapor transmission rate: Put a certain amount of anhydrous calcium chloride into a weighing bottle, seal the weighing bottle with a fiber membrane, and then put the weighing bottle into a desiccator filled with deionized water. Weigh it after 24 hours. Calculate the WVP of the fiber membrane using the following formula:

[0046] WVP(g·m -1 ·s -1 ·Pa)=(W×D) / (t×A×△P)

[0047] Where W is the weight added to the weighing bottle (g), D is the thickness of the fiber membrane (m), t is the time length (s), and A is the area of ​​the weighing bottle (m 2 ), ΔP is the vapor pressure difference between the inside and outside of the beaker (3567Pa).

[0048] The effect of CNC on the barrier properties of fiber membranes can be seen through the determination of water vapor permeability. Table 2 shows the water vapor permeability of nanofiber membranes with different CNC addition amounts and nanocellulose fiber films with 3% addition. It can be seen from Table 2 that the water vapor permeability of the group with CNC addition is significantly lower than that of the 0% group (p<0.05), among which the 3% group has the lowest water vapor permeability, and the water vapor permeability of the 4.5% and 6% groups are significantly higher than that of the 3% group (p<0.05). It can be seen that the addition of CNC reduces the water vapor permeability of the fiber membrane and improves the barrier properties of the fiber membrane; but excessive CNC will also cause the barrier properties of the fiber membrane to deteriorate. This is consistent with the results of tensile strength, and can also be explained by the dense network formed between CNC and the fiber membrane matrix. It is this network that plays a role in blocking water vapor and improving the tensile strength of the fiber membrane.

[0049] In addition, compared with the film with added nanocellulose fibers (3%), under the same concentration conditions, the water vapor permeability of the film with added CNC is lower, indicating that CNC has higher barrier properties than nanocellulose fibers.

[0050] Table 2 Water vapor permeability of nanofiber membranes with different CNC addition amounts and nanocellulose fiber films with 3% addition

[0051]

[0052] Note: The mean values ​​with different superscripts (ad) are significantly different (p<0.05, n=3).

[0053] 3.4 X-ray diffraction (XRD): The XRD patterns of the five fiber membranes were tested using a D2 Phaser X-ray diffractometer (Bruker, Germany) with a scanning angle of 5 to 90° and a scanning speed of 1° / min.

[0054] XRD patterns show the effect of CNC on the crystallinity of fiber membranes. Figure 2 XRD patterns of electrospun nanofiber membranes with different CNC contents. Figure 2 It can be seen that the five groups of fiber membrane samples have the same diffraction peaks, and no new peaks appear due to the change in CNC content. However, the peak intensities are obviously different. It can be seen that the intensities of several diffraction peaks in the group with added CNC, such as 31.4° and 45.2°, are stronger than those in the 0% group, which shows that high-crystallinity CNC can improve the crystallinity of the fiber membrane by combining with the fiber membrane matrix. This is also proof that CNC combines with the fiber membrane matrix to form a dense network, and it is also the reason why the barrier properties and tensile strength of the fiber membrane are improved after the addition of CNC.

[0055] Based on the above characterization results, it can be found that 3% C-OZP has the best comprehensive performance in tensile strength, elongation at break and water vapor permeability, so 3% C-OZP was selected for the next step of the cold fresh pork preservation experiment.

[0056] The 3% C-OZP fiber membrane with the best barrier properties was selected for pork preservation, and TVC ( Figure 3 )、TVB-N( Figure 4 ) level to judge the freshness of pork during storage.

[0057] The specific steps are as follows: Take fresh pork from the slaughterhouse 24 hours after slaughter, cut it into small pieces (about 5×3×1cm 3 ) into a small fresh-keeping box (6.6×5.5×3.5cm 3 ) and divided into 3 groups: one control group without any treatment; one control group wrapped with ZP film; one control group wrapped with 3% C-OZP film. Pork samples were taken out at 0, 3, 6, and 9 days of storage to determine their total bacterial count (TVC) and volatile basic nitrogen (TVB-N). The determination method refers to GB 4789.2-2022 and GB5009.228-2016.

[0058] Figure 3 The TVC curves of pork in different treatment groups during storage. Figure 4 The curves of TVB-N changes of pork in different treatment groups during storage are shown in the figure. As can be seen from the figure, the control group selected pork that was not treated with anything and pork covered with ZP film without adding essential oil and CNC. Since there is no active substance in the ZP film, the TVC and TVB-N curves of the two control groups basically overlap. In contrast, the 3% C-OZP group showed a trend of delaying the growth of TVC and TVB-N. In the TVC curve, the total viable count of the CK group and the ZP group exceeded 6log CFU / g on the 6th day, while the 3% C-OZP group only had 5.37±0.25log CFU / g. According to the curve, it can be seen that the TVC of the pork in the CK group and the ZP group reached the critical point of deterioration on about the 5th day; while the 3% C-OZP group reached it after about the 7th day. Similarly, in the TVB-N curve, the TVB-N value of pork in the CK group and ZP group reached 15 mg / 100 g on about the 5th day, reaching the critical point of deterioration; the 3% C-OZP group reached it at about 7 days. The above can show that the pork in the 3% C-OZP group has a longer shelf life than the CK group and ZP group, and the nanofiber membrane added with 3% CNC can effectively reduce the growth of TVC and TVB-N during pork storage, and extend the shelf life of pork by about 2 days.

[0059] The present invention studies the effect of passion fruit peel-derived CNC on Zein / PEO electrospun nanofiber membrane loaded with oregano essential oil, and finally applies it to pork preservation. Characterization of the fiber membrane shows that CNC can improve the tensile strength and water vapor barrier of the fiber membrane by forming a dense network with high crystallinity. The 3% CNC-ZP membrane is applied to pork preservation, which can extend the shelf life of pork by about 2 days in 4-degree storage.

[0060] The present invention provides a nanofiber membrane containing cellulose nanocrystals and a preparation method and application thereof. 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 protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for preparing a nanofiber membrane containing cellulose nanocrystals, characterized in that: The specific steps are: dissolving zein, polyethylene oxide and cellulose nanocrystals in acetic acid solution, mixing evenly and adding oregano essential oil to obtain spinning solution; electrospinning the spinning solution to obtain a nanofiber membrane containing cellulose nanocrystals.

2. The preparation method according to claim 1, characterized in that: The mass ratio of zein to polyethylene oxide is 99:

1.

3. The preparation method according to claim 1, characterized in that: The added amount of the cellulose nanocrystals is 1.5-6% of the total mass of zein and polyethylene oxide.

4. The preparation method according to claim 3, characterized in that: The source of the cellulose nanocrystals is purple passion fruit peel.

5. The preparation method according to claim 1, characterized in that: The concentration of the acetic acid solution is 70% v / v; the mass volume ratio of the total mass of the zein and polyethylene oxide to the acetic acid solution is 1 g:5 ml.

6. The preparation method according to claim 1, characterized in that: The added amount of the oregano essential oil is 50% to 60% of the total mass of zein and polyethylene oxide.

7. The preparation method according to claim 1, characterized in that: The electrostatic spinning is carried out under the following parameters: flow rate 0.0012 mm / s, voltage 15-16 kV, temperature 25±5° C., humidity 40-50%, and needle head 15 cm away from the receiving plate.

8. A nanofiber membrane containing cellulose nanocrystals prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the nanofiber film containing cellulose nanocrystals as claimed in claim 8 in preparing packaging for delaying meat deterioration.

10. The use according to claim 9, characterized in that: The application is the use of a nanofiber membrane containing cellulose nanocrystals in the preparation of packaging for delaying the deterioration of pork.

Images