Preparation method of low-temperature plasma modified chitosan nano-composite film and application of low-temperature plasma modified chitosan nano-composite film in fresh keeping of fish meat

Abstract

The invention discloses a preparation method of a low-temperature plasma modified chitosan nano-composite membrane and application of the low-temperature plasma modified chitosan nano-composite membrane in fish preservation, the composite membrane is prepared by taking chitosan as a matrix, and coating curcumin / quercetin / zein nano-particles (ZCQC NPs) with chondroitin sulfate treated by low-temperature plasma (CP). The mechanical property (the tensile strength reaches 61.96 Mpa, and the elongation at break reaches 41.90%), the moisture resistance (the water vapor transmission rate is reduced by 42%, and the oxygen transmission rate is reduced by 54%) and the antioxidant activity (the DPPH removal rate is 78.06%, and the ABTS removal rate is 63.40%) of the film are remarkably improved. In the application of fresh keeping of fish meat, the film can effectively inhibit microbial growth and lipid oxidation. The invention provides an efficient and degradable solution for active packaging of aquatic products.

Description

Technical Field

[0001] The present invention belongs to the technical field of bio-based active packaging materials, and in particular relates to a method for preparing a low-temperature plasma-modified chitosan nanocomposite film and its application in fish preservation. Background Art

[0002] Aquatic products are susceptible to spoilage due to their high moisture content and endogenous enzyme activity. Existing plastic packaging is non-degradable and inactive. Effective preservation solutions are urgently needed to extend shelf life, maintain nutritional value and quality, and expand the market reach of aquatic product manufacturers. With increasing consumer demand, environmentally friendly biomaterials are gaining increasing attention in food packaging due to their renewable, abundant, and biodegradable properties.

[0003] Pure chitosan membranes have broad application potential due to their biodegradability, biocompatibility, antimicrobial activity, nontoxicity, and multifunctional chemical and physical properties. However, they suffer from problems such as low mechanical strength, poor moisture barrier properties, and uneven dispersion of nanoparticles.

[0004] Nanoparticles prepared by traditional blending methods are prone to agglomeration, and low-temperature plasma treatment is mostly used for surface modification. However, there has been no report on its use for synergistic enhancement of the nanoparticle-chitosan interface. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a low-temperature plasma modified chitosan nanocomposite membrane.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for preparing a low-temperature plasma modified chitosan nanocomposite film, comprising:

[0009] Curcumin and zein were dissolved in an ethanol solution, stirred, and then added with distilled water. The ethanol was removed by rotary evaporation to prepare a curcumin-zein nanosuspension.

[0010] The quercetin solution was added dropwise to the curcumin-zein nanosuspension and stirred evenly to prepare the quercetin-curcumin-zein nanosuspension;

[0011] The quercetin-curcumin-zein nanosuspension was added dropwise to the chondroitin sulfate solution and stirred evenly to prepare a chondroitin sulfate composite nanosuspension;

[0012] Chitosan is dissolved in acetic acid to prepare chitosan solution, chondroitin sulfate composite nano suspension and plasticizer are added, stirred and ultrasonically defoamed to prepare membrane solution;

[0013] The film liquid is formed into a film by a casting method, and an active packaging film is obtained after drying;

[0014] The obtained active packaging film is placed in a low-temperature plasma device, with air as the working gas, and treated for 2 minutes under the conditions of voltage 0-50 kV and frequency 120 KHz to obtain a modified film.

[0015] As a preferred embodiment of the preparation method of the present invention, the curcumin-zein nanosuspension has a curcumin concentration of 1-5 mg / mL and a zein concentration of 5-10 mg / mL.

[0016] As a preferred embodiment of the preparation method of the present invention, the concentration of the quercetin solution is 1-5 mg / mL, and the volume ratio of the quercetin solution to the curcumin-zein nanosuspension is 5-20:100.

[0017] As a preferred embodiment of the preparation method of the present invention, the concentration of the chondroitin sulfate solution is 1-5 mg / mL, and the volume ratio of the quercetin-curcumin-zein nanosuspension to the chondroitin sulfate solution is 50-100:50-100.

[0018] As a preferred solution of the preparation method of the present invention, the mass fraction of the chitosan solution is 2-5%, the nano suspension accounts for 1-10% of the total mass of the membrane liquid, and the plasticizer accounts for 20-50% of the total mass of the membrane liquid.

[0019] As a preferred embodiment of the preparation method of the present invention, the plasticizer is glycerol.

[0020] As a preferred embodiment of the preparation method of the present invention, the drying temperature is 35 to 50° C., and the drying time is 24 to 30 hours.

[0021] Another object of the present invention is to overcome the deficiencies in the prior art and provide a composite chitosan-based membrane.

[0022] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a composite chitosan-based film in the field of food packaging, wherein the food includes high-moisture content or perishable food.

[0023] Another object of the present invention is to overcome the deficiencies in the prior art and provide a composite chitosan-based membrane for use in fish preservation, comprising:

[0024] Wrap the fish meat with the active packaging film and store at 4°C;

[0025] The freshness of fish meat is determined by the color change of the fish meat, where the color change is linearly correlated with the release of fish spoilage products.

[0026] Beneficial effects of the present invention:

[0027] (1) Mechanical properties: tensile strength reaches 61.96 MPa (67% higher than pure chitosan film);

[0028] (2) Barrier performance: strong moisture barrier (water vapor transmission rate is 3.84×10 -6 g / m·d·Pa, oxygen transmission rate is 1.07g / m·d);

[0029] (3) Biological activity: The modified composite membrane exhibited significant antioxidant activity and antibacterial effects;

[0030] (4) Preservation effect: The shelf life of fish meat was extended to 8 days at 4°C (4 days for the control group). BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0032] Figure 1 Characterization diagram of the nanoparticles of the present invention, wherein A is a scanning electron microscope (SEM) image, B is the particle size and zeta potential, and C is the infrared spectrum (FT-IR).

[0033] Figure 2 Figure 1 is a structural characterization diagram of the composite film of the present invention, wherein A is the SEM morphology, B is the ATR-FTIR spectrum, and C is the X-ray diffraction pattern (Chitosan: pure chitosan film; C-NPs 0kV: nanoparticle composite chitosan film without low-temperature plasma treatment; C-NPs 10 / 30 / 50kV: nanoparticle composite chitosan film treated with low-temperature plasma at different voltages).

[0034] Figure 3 Mechanical properties of different films prepared in this invention.

[0035] Figure 4Graph showing the barrier performance of the composite film of the present invention.

[0036] Figure 5 Graph showing the optical performance of the composite film of the present invention, wherein A is the transmittance curve and B is the physical appearance.

[0037] Figure 6 Graphs showing the biological activity of the composite film of the present invention, wherein AB represents the thermal stability graph, C represents the antioxidant activity graph, and D represents the antibacterial activity graph.

[0038] Figure 7 The figure shows the effect of different composite films of the present invention on fish preservation, wherein A is the pH value, B is the TBARS value (lipid oxidation), C is the TVB-N value (volatile basic nitrogen), D is the change curve of TVC (total bacterial count), and E is the visual appearance of fish blocks at different storage periods (Control: without any film wrapping; PE: polyethylene film; Chitosan: pure chitosan film; C-NPs: nanoparticle composite chitosan film without low-temperature plasma treatment; CP-C-NPs: nanoparticle composite chitosan film treated with low-temperature plasma at a voltage of 30 kV). DETAILED DESCRIPTION

[0039] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0040] In the present invention, chitosan with a deacetylation degree of ≥95% and a MW of 50,000-60,000 was purchased from Shandong Keyuan Biochemical Co., Ltd., and other raw materials were common commercial products.

[0041] Low-temperature plasma processing equipment: Equipment model: BK130 / 36 dielectric barrier discharge (DBD) system;

[0042] Manufacturer: Phoenix Electric Co. Ltd. (USA);

[0043] Equipment type: atmospheric pressure low-temperature plasma generator.

[0044] Example 1

[0045] Preparation and characterization of nanoparticle suspensions:

[0046] (1) Preparation of nanoparticle suspension

[0047] Curcumin (3 mg / mL) and zein (8 mg / mL) were dissolved in 70% ethanol solution and magnetically stirred for 30 min until completely dissolved;

[0048] Slowly inject the above solution into 30 times the volume of distilled water and continue stirring for 1 hour;

[0049] Ethanol was removed using a rotary evaporator (40 °C, 100 rpm) to obtain a curcumin / zein nanosuspension;

[0050] The quercetin solution was added dropwise to the curcumin / zein suspension at a volume ratio of 15:100 and stirred for 2 h;

[0051] The quercetin / curcumin / zein suspension was mixed with the chondroitin sulfate solution at a volume ratio of 80:80 and stirred at 4°C for 6 h to obtain the chondroitin sulfate / quercetin / curcumin / zein nanosuspension (ZCQC).

[0052] (2) Structural characterization

[0053] The morphology of the freeze-dried nanoparticles was observed by SEM (accelerating voltage 10 kV); the particle size distribution and zeta potential were determined by laser particle size analyzer; the functional group changes of the nanoparticle components were analyzed by FT-IR (resolution 4 cm -1 ,4000-500cm -1 ).

[0054] Figure 1 A It can be observed that the ZCQC nanoparticles are spherical, with smooth surface and uniform particle size distribution; the average diameter of the nanoparticles is 1518.20nm and the zeta potential is -36.76mV, indicating that the electrostatic repulsion maintains stability (see Figure 1 B); from Figure 1 C infrared spectrum shows that compared with the characteristic peak of zein, the hydroxyl peak in the nanoparticles is from 3446 cm -1 Move to 3411cm -1 , amide II peak from 1546cm -1 Move to 1519cm -1 , confirming the formation of hydrogen bonds and hydrophobic interactions. The number of hydrogen bonds in the nanoparticles increased after low-temperature plasma treatment, thereby enhancing the stability of the complex.

[0055] Example 2

[0056] Preparation and structural characterization of low-temperature plasma modified composite films:

[0057] (1) Preparation of composite membrane solution

[0058] Chitosan (2 wt %) was dissolved in 1% acetic acid, nanoparticle suspension (5 wt %) and glycerol (30 wt %) were added, and the mixture was degassed by ultrasonication;

[0059] (2) Film forming process

[0060] The composite film was also poured into a petri dish to form a film, and dried at 50°C for 26 h;

[0061] (3) Low-temperature plasma treatment

[0062] The composite film was treated in dielectric barrier discharge mode (voltage 0 / 10 / 30 / 50 kV, frequency 120 kHz, time 2 min).

[0063] (4) Structural characterization

[0064] The microstructure of the modified nanocomposite film was observed by scanning electron microscopy; the bond changes between the components of the composite film were determined by ATR-FTIR; and the crystal structure of the film was determined by XRD.

[0065] like Figure 2 As shown in ABC, A is the micromorphology of the modified nanocomposite film, B is the ATR-FTIR spectrum of the modified nanocomposite film, and C is the XRD spectrum of the modified nanocomposite film.

[0066] It can be seen from the SEM image that as the treatment voltage increases, the surface of the composite film becomes smoother, flatter and denser, with no obvious cracks and voids; ATR-FTIR confirms that the amino group (-NH2) of chitosan forms hydrogen bonds with the carboxyl group (-COOH) of the nanoparticles; XRD results further show that low-temperature plasma treatment reduces the crystallinity of the composite film, which is attributed to the restricted free movement of the chitosan chain.

[0067] Example 3

[0068] Physical property test of modified composite film:

[0069] (1) Mechanical properties

[0070] The tensile strength (TS) and elongation at break (EAB) of the films were tested by a texture analyzer.The films were cut into 20 mm × 80 mm strips with a gap of 40 mm between the clamps.

[0071] from Figure 3 The mechanical properties test results show that the TS and EAB of the pure chitosan film are 37.21MPa and 22.42%, respectively, while those of the C-NPs 0kV film are increased to 44.90MPa and 25.52%, respectively. This result shows that the addition of nanoparticles significantly improves the mechanical properties of the film.

[0072] More notably, as the plasma treatment voltage increases, the TS and EAB of the film show a continuous upward trend, which is mainly attributed to the plasma treatment promoting a more complete cross-linking reaction between chitosan molecular chains.

[0073] (2) Barrier properties

[0074] The film (70 mm x 70 mm) was sealed in a beaker containing 5 g of calcium chloride and 5 g of deoxidizer. After being placed at 25°C and 75% relative humidity for 48 hours, the cup was weighed and the water vapor transmission rate and oxygen transmission rate of the film were calculated:

[0075] WVP=(Δm×d) / (A×t×ΔP)

[0076] OP=(Δm×d) / (A×t)

[0077] Where Δm is the mass increment (g), d is the film thickness (mm), and A is the permeation area (m 2 ), t is the time interval (s), and ΔP is the water vapor pressure difference across the film (2.945 kPa).

[0078] from Figure 4 It can be seen that CP modification significantly improved the hydrophobicity of chitosan-based films (P < 0.05), which was mainly due to the CP treatment inducing Schiff base reaction between chitosan molecular chains, thereby reducing the number of hydrophilic groups on the film surface.

[0079] (3) Optical performance

[0080] The color of the film (50 mm×50 mm) was measured using a colorimeter for L*, a*, and b*, and the transmittance at 200-800 nm was measured using an ultraviolet spectrophotometer.

[0081] The test results of color parameters of different films are shown in Table 1.

[0082] Table 1

[0083]

[0084] The results in Table 1 show that the a* and b* values of the composite films increased significantly after CP treatment (P < 0.05), indicating that the color of the film shifted toward reddish-yellow tones, which may be due to the oxidation of the color-developing components during the treatment process.

[0085] like Figure 5 As shown in Figures AB, the transmittance of the film decreases in a dose-dependent manner as the treatment voltage increases, which is attributed to: (1) the light absorption properties of the nanoparticles; and (2) the enhanced light scattering caused by the cross-linked polymer network. This structural change enables the film to exhibit excellent UV-visible light blocking properties.

[0086] Example 4

[0087] Functional stability test of modified composite film:

[0088] (1) Thermal stability

[0089] Approximately 3 to 10 mg of film fragments were placed in an aluminum crucible, with an empty crucible used as a reference and nitrogen as the transfer gas. Differential scanning calorimetry (DSC) and thermogravimetric (TG) curves were obtained at a heating rate of 10°C / min over the temperature ranges of 20°C–200°C and 30°C–700°C, respectively.

[0090] like Figure 6 As shown in AB, A is the DSC curve and B is the TG curve.

[0091] Thermal analysis results show that the heat deformation temperature of the chitosan film is 151.22°C, while that of the C-NPs composite film increases to 152.46°C, confirming that the introduction of nanoparticles enhances the thermal stability of the material. The heat deformation temperature decreases with increasing CP treatment voltage, likely due to the structural modification of the material by CP.

[0092] TG analysis revealed a significantly higher residual rate in the nanocomposite film compared to pure chitosan film, indicating that the non-volatile components of the nanoparticles contribute to the material's improved thermal stability. In particular, the mass loss rate of the CP-treated sample in the high-temperature region was significantly reduced, attributed to the dense cross-linked network induced by CP, which effectively suppressed the volatilization of thermal decomposition products. This significantly improved thermal performance not only broadens the processing window of the composite material but also provides reliable support for its practical application in high-temperature environments.

[0093] (2) Antioxidant activity

[0094] Immerse the film sample in distilled water, centrifuge, and mix 1 mL of the supernatant with 1 mL of 0.05 mM DPPH solution. Incubate in the dark for 30 minutes, and measure absorbance at 517 nm. Subsequently, mix 7 mM ABTS with 2.45 mM potassium persulfate and incubate overnight in the dark. Incubate the film sample with 20 mL of ABTS working solution (25°C, 30 minutes, in the dark), and measure absorbance at 734 nm.

[0095] The free radical scavenging rate was calculated according to the following equation:

[0096] Free radical scavenging rate (%) = (A0-A1) / A0×100;

[0097] Where A1 and A0 are the absorbance of the test sample and the control sample, respectively.

[0098] like Figure 6 As shown in Figure C, the introduction of nanoparticles significantly enhanced the antioxidant activity of the chitosan-based composite membrane (P < 0.05), which was mainly attributed to the synergistic free radical scavenging effect between NPs and chitosan. After CP modification, the uniform dispersion of NPs in the membrane further improved the antioxidant performance.

[0099] (3) Antibacterial activity

[0100] The antibacterial activity of the film solution (50 mg of film sample was reconstituted in 10 mL of distilled water) was determined using a 96-well plate assay. Samples (200 μL) were added to the 96-well plate, with sterile water used as a control. Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhimurium, and Listeria monocytogenes were inoculated and the inhibition rate was measured after 24 hours of incubation.

[0101] from Figure 6 As shown in Figure 4, the nanocomposite film exhibited a significant inhibitory effect on foodborne pathogens (P < 0.05), and the antibacterial effect increased with increasing CP treatment voltage. This phenomenon is attributed to the synergistic effect of CP treatment on the antibacterial properties of chitosan and NPs, confirming the application potential of this film in active food packaging.

[0102] Example 5

[0103] Application of composite film in fish preservation:

[0104] In actual application tests, the composite film was used to preserve fish fillets refrigerated at 4°C. The results showed:

[0105] Changes in fish meat when stored at 4°C Figure 7 ABCDE, where A represents pH change, B represents TBARS value change, C represents TVB-N value change, D represents total colony count change, and E represents the appearance of fish meat.

[0106] The quality changes of fish meat during storage at 4℃ are as follows: Figure 7 AE shown:

[0107] The pH value shows a trend of first decreasing (due to the degradation of glycogen to produce lactic acid) and then increasing (due to the production of alkaline compounds by the action of endogenous enzymes and microorganisms);

[0108] The continued rise in TBARS values indicated increased fat oxidation, while changes in TVB-N values showed that the control group exceeded the spoilage threshold of 20 mg / 100 g on day 4, while the CP-C-NPs group delayed this threshold until day 8, consistent with the accumulation of volatile nitrogen compounds produced by protein degradation. TVC analysis further confirmed that the CP-C-NPs group had the greatest antibacterial effect, with a significantly lower colony growth rate than the other groups (P < 0.05).

[0109] Figure 7 E intuitively demonstrated the difference in freshness preservation between different packaging groups - after 4 days of storage, the fish meat in the unpackaged group, PE film group and pure chitosan film group had obviously deteriorated, while the fish meat in the C-NPs and CP-C-NPs groups maintained good color and texture due to the synergistic effect of the film's UV blocking and antioxidant properties, and the shelf life was extended to 8 days.

[0110] The composite film prepared by the present invention is particularly suitable for the field of fresh-keeping packaging of aquatic products and can significantly extend the shelf life.

[0111] The present invention utilizes a unique process of "film formation followed by plasma treatment," which is fundamentally different from conventional blending modification methods. Plasma treatment, as a non-thermodynamically balanced surface modification technology, can achieve precise modification of the film surface without altering the properties of the base material. This invention has achieved unexpected technical results:

[0112] (1) Synergistic effect: After plasma treatment, the following unpredictable changes occur on the film surface: increased surface free radical density (anti-oxidation results), increased surface hydrogen bond functional groups (FT-TR test results), and reduced surface roughness (SEM test results).

[0113] (2) Significant improvement in performance indicators:

[0114] Improved antioxidant activity (DPPH and ABTS test results), far exceeding conventional blending modification;

[0115] The antibacterial efficiency is improved and the effectiveness is extended by 2 times.

[0116] Unpredictability of the technical effects of the present invention:

[0117] (1) Existing technology shows that plasma treatment usually causes oxidation damage to the material surface. However, this case unexpectedly discovered that under specific parameters (50kV / 120kHz / 2min), a nanoscale cross-linked structure can be formed, which not only maintains mechanical strength but also enhances the anchoring effect of active components.

[0118] (2) SEM observations confirmed that plasma treatment formed a uniform nanoscale pit structure on the surface. This unique morphological feature provided a directional loading site for the active components, an effect that cannot be achieved through conventional blending processes.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. A method for preparing a low-temperature plasma-modified chitosan nanocomposite membrane, characterized in that: include, Curcumin and zein were dissolved in an ethanol solution, stirred, and then added with distilled water. The ethanol was removed by rotary evaporation to prepare a curcumin-zein nanosuspension. The quercetin solution was added dropwise to the curcumin-zein nanosuspension and stirred evenly to prepare the quercetin-curcumin-zein nanosuspension; The quercetin-curcumin-zein nanosuspension was added dropwise to the chondroitin sulfate solution and stirred evenly to prepare a chondroitin sulfate composite nanosuspension; Chitosan is dissolved in acetic acid to prepare chitosan solution, chondroitin sulfate composite nano suspension and plasticizer are added, stirred and ultrasonically defoamed to prepare membrane solution; The film liquid is formed into a film by a casting method, and an active packaging film is obtained after drying; The obtained active packaging film is placed in a low-temperature plasma device, with air as the working gas, and treated for 2 minutes under the conditions of voltage 0-50 kV and frequency 120 KHz to obtain a modified film.

2. The preparation method according to claim 1, wherein: The curcumin-zein nanosuspension has a curcumin concentration of 1-5 mg / mL and a zein concentration of 5-10 mg / mL.

3. The preparation method according to claim 1 or 2, wherein: The concentration of the quercetin solution is 1-5 mg / mL, and the volume ratio of the quercetin solution to the curcumin-zein nanosuspension is 5-20:

100.

4. The preparation method according to claim 3, wherein: The concentration of the chondroitin sulfate solution is 1-5 mg / mL, and the volume ratio of the quercetin-curcumin-zein nanosuspension to the chondroitin sulfate solution is 50-100:50-100.

5. The preparation method according to claim 1 or 4, wherein: The mass fraction of the chitosan solution is 2-5%, the nano suspension accounts for 1-10% of the total mass of the membrane liquid, and the plasticizer accounts for 20-50% of the total mass of the membrane liquid.

6. The preparation method according to claim 5, wherein: The plasticizer is glycerol.

7. The preparation method according to claim 1 or 6, wherein: The drying temperature is 35 to 50° C., and the drying time is 24 to 30 hours.

8. A chitosan nanocomposite film prepared by the preparation method according to any one of claims 1 to 7.

9. Application of the chitosan nanocomposite film according to claim 8 in the field of food packaging, characterized in that: Such foods include high moisture content or perishable foods.

10. The use of the chitosan nanocomposite film according to claim 8 in preserving fish, characterized in that: include, Wrap the fish meat with the active packaging film and store at 4°C; The freshness of fish meat is determined by the color change of the fish meat, where the color change is linearly correlated with the release of fish spoilage products.

Images