A preparation method of a high-toughness chitosan-based intelligent film with preservation and visual monitoring of fish meat freshness

Abstract

The application discloses a preparation method of a high-toughness chitosan-based intelligent film with preservation and visual monitoring of fish freshness, which comprises the following steps: firstly, co-coating curcumin and quercetin into zein and chondroitin sulfate to obtain nanoparticles with a core-shell structure; secondly, adding the nanoparticles into a chitosan acetic acid solution; thirdly, adding a plasticizer glycerol, stirring, ultrasonic degassing, and then obtaining a film-forming solution; and finally, drying the film-forming solution at a certain temperature to form the intelligent film. The application creatively co-embeds natural indicators curcumin and quercetin with excellent antioxidant properties to obtain nanoparticles with a core-shell structure, the incorporation of the nanoparticles effectively improves the physical properties and biological activity of the chitosan film, the visual intelligent indicator film is sensitive to the response of the change of the pH value in the environment, can accurately feed back the freshness information of fish and meat food, and is expected to be applied to real-time monitoring of food freshness.

Description

Technical Field

[0001] This invention belongs to the field of green and intelligent food packaging, specifically involving a method for preparing a high-toughness chitosan-based intelligent film that can preserve freshness and provide visual monitoring of the freshness of fish. Background Technology

[0002] Billions of tons of food are wasted each year. While efforts have been made to better map the spoilage patterns of each type of food, spoilage is highly influenced by environmental conditions, making it a non-standardized process. Smart packaging can simultaneously meet the need to improve food quality and monitor food freshness in real time. However, plastics remain the dominant market for food packaging materials, especially since the start of pandemics like COVID-19, which have led to a global shift from reusable to single-use containers. These petroleum-based plastic packaging materials pose a threat to marine environments and human health due to their non-degradable nature. Meanwhile, many countries have issued "plastic bans" to prevent the problem from worsening, while encouraging the gradual replacement of petroleum-based plastics with packaging films made from environmentally friendly biomaterials such as proteins and carbohydrates.

[0003] Chitosan, as a common bio-edible packaging material, has high transparency and good film-forming properties. However, its weak mechanical properties and high brittleness are not conducive to its use in packaging materials.

[0004] Therefore, designing and fabricating chitosan films that possess both high toughness and functional and indicative properties has always been a desirable goal. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

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

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a highly resilient chitosan-based smart membrane that can preserve and visually monitor the freshness of fish.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a high-toughness chitosan-based smart membrane with preservation and visual monitoring capabilities for fish freshness, comprising,

[0009] Curcumin and zein were dissolved in an ethanol solution, stirred, and the resulting solution was injected into distilled water. The ethanol was then removed using a rotary evaporator to obtain a curcumin / zein nano suspension.

[0010] Quercetin solution was added dropwise to curcumin / zein nano suspension and stirred evenly to obtain quercetin / curcumin / zein nano suspension.

[0011] Quercetin / curcumin / zein nano suspension was added dropwise to chondroitin sulfate solution, stirred evenly, and then freeze-dried to obtain nanoparticles.

[0012] Chitosan was dissolved in acetic acid to prepare a chitosan solution. Nanoparticles and plasticizers were added to the chitosan solution, and the solution was stirred and ultrasonically degassed to obtain an active layer coating liquid.

[0013] The prepared coating solution is evenly placed in a film-forming container and dried in an oven to form a smart film.

[0014] As a preferred embodiment of the preparation method described in this invention, the curcumin / zein nano-suspension has a curcumin concentration of 1-3 mg / mL and a zein concentration of 10-15 mg / mL.

[0015] In a preferred embodiment of the preparation method described in this invention, the concentration of the quercetin solution is 1–3 mg / mL.

[0016] In a preferred embodiment of the preparation method described in this invention, the volume ratio of the quercetin solution to the curcumin / zeatin nano-suspension is 0.5 to 2:5.

[0017] In a preferred embodiment of the preparation method described in this invention, the concentration of the chondroitin sulfate solution is 1-3 mg / mL, and the volume ratio of the quercetin / curcumin / zeatin nano-suspension to the chondroitin sulfate solution is 80-90:20-40.

[0018] In a preferred embodiment of the preparation method described in this invention, the active layer coating liquid contains chitosan at a mass fraction of 2-4%, nanoparticles at a mass fraction of 1-5%, and plasticizer at a mass fraction of 25-40%.

[0019] In a preferred embodiment of the preparation method described in this invention, the plasticizer is glycerol.

[0020] In a preferred embodiment of the preparation method described in this invention, the drying process forms a smart membrane, wherein...

[0021] The drying temperature is 40-50℃, and the drying time is 20-24 hours.

[0022] Another objective of this invention is to overcome the shortcomings of the prior art and provide a product obtained by a method for preparing a high-toughness chitosan-based smart membrane that has the functions of preserving freshness and visually monitoring the freshness of fish.

[0023] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a high-toughness chitosan-based smart membrane in detecting the freshness of fish, comprising,

[0024] Fresh fish is placed in a box with an intelligent indicator film and stored, transported, or sold at 4°C.

[0025] Take photos of the packaging boxes with the smart indicator film, record the image information of the smart indicator film, and determine its freshness.

[0026] Beneficial effects of this invention:

[0027] (1) This invention uses inexpensive, biocompatible, and biodegradable chitosan as the main film-forming matrix and adds nanoparticles to improve its mechanical properties. The tensile strength of the high-precision indicator film material prepared is 38.81-61.92 MPa and the elongation at break is 44.71-60.96%.

[0028] (2) This invention uses chitosan as the main film-forming material and utilizes the nucleophilic reaction between nanoparticles and chitosan to form a film, which is then stretched to form a film. This results in a smart film with good mechanical properties and edibility, and it can accurately indicate the freshness of fresh aquatic products with high indication stability. This invention realizes the intelligent packaging film for aquatic products and has considerable application value in the intelligent packaging of aquatic products.

[0029] (3) The freshness indicator film prepared by the present invention has greater color change difference and higher color development sensitivity under different pH conditions. The early spoilage and deterioration of aquatic products can be intuitively judged based on the color change of the freshness indicator film. The freshness of aquatic products can be quickly and non-destructively detected without the need for other instruments.

[0030] (4) The present invention is simple to operate, easy to control, highly operable, and suitable for industrial production. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0032] Figure 1 The diagram shows the mechanical properties of the membranes in the comparative examples and embodiments of the present invention. In this diagram, CS / FeS film is a chitosan / iron sulfide membrane, CS / CeNPs film is a chitosan / cerium oxide membrane, CS / FNF film is a chitosan / silk fibroin nanofiber membrane, CS / KC / FLE film is a chitosan / kaolinite clay / fig membrane, and PP film is an LDPE film.

[0033] Figure 2 This is a diagram showing the membrane moisture barrier properties of the comparative example and various embodiments in this invention.

[0034] Figure 3 This is a diagram showing the antioxidant activity of the membranes in the comparative examples and various embodiments of the present invention.

[0035] Figure 4 The diagram shows the antibacterial activity of the membrane in the comparative examples and various embodiments of the present invention.

[0036] Figure 5 The graph shows the following: (A) pH sensitivity, (B) ammonia and acid sensitivity, (C) indication of fish freshness, (D) changes in pH and TVB-N of fish stored at 4°C, and (E) color changes of fish stored at 4°C.

[0037] Figure 6 This is a particle size distribution diagram of the nanoparticles in this invention.

[0038] Figure 7 The images show the SEM (A), XRD (B), and FTIR (C) images of the membrane in this invention. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0041] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0042] The key performance testing standards for the bilayer membrane involved in this invention are as follows:

[0043] 1. Nanoparticle size and characterization analysis:

[0044] The particle size distribution, dispersion index (PDI), and zeta potential of the nanoparticles were measured at 25 °C using a potentiometer; the morphological characteristics of the nanoparticles were measured using a scanning electron microscope at an accelerating voltage of 10 kV.

[0045] Fourier transform infrared spectrometer is used to measure wavenumbers in the range of 4000-400 cm⁻¹. -1 Nanoparticles. The encapsulation efficiency and loading of curcumin and quercetin were determined using ultrasound-assisted extraction.

[0046] 2. Mechanical properties

[0047] Following ASTM standard (D882-02), elongation at break and tensile strength were measured using a TA texture analyzer. Tensile strength (TS) and elongation (EB) were determined after the membrane samples were cut into rectangular samples 10 mm wide and 70 mm long.

[0048] 3. Water vapor permeability

[0049] Weigh 3g of anhydrous CaCl2 into a weighing bottle, cover the bottle opening with a composite membrane, weigh again and record m0. Place the bottle in a constant temperature and humidity chamber, maintain 90% relative humidity at 23℃ for 24 hours, weigh again and record m1. Calculate the water vapor permeability based on the change in mass. The water vapor permeability is calculated using the following formula:

[0050] In the formula: Δm (kg) - the difference in mass of the weighing bottle; d (mm) - the thickness of the membrane; t (s) - time; A (m2) - the effective area of ​​the membrane; P (kPa) - the water vapor pressure difference inside and outside the membrane.

[0051] 4. Moisture content, water solubility, and swelling degree

[0052] Weigh a 2×2cm membrane (W0), dry it at 105℃ for 24 hours, and then weigh it (W1);

[0053] The dried film was then soaked in 50 mL of distilled water for 24 hours. After removing the surface water with absorbent paper, the weight of the film (W2) was measured and dried in an oven at 105 °C until constant weight (W3).

[0054] The moisture content, water solubility, and swelling degree of the film are determined by the following formula:

[0055]

[0056]

[0057]

[0058] 5. Color and opacity

[0059] The color of the film was measured using a colorimeter (SC-80C, Beijing, China). The L* (brightness), a* (red-grayscale), and b* (yellow-bluescale) parameters were determined by reflectance measurements. Opacity was measured using a UV spectrophotometer. The film size was 10 mm × 40 mm. An empty quartz dish was used as a reference. The opacity was calculated as follows:

[0060]

[0061] Where A600 is the absorbance and d (mm) is the film thickness.

[0062] 6. Determination of the antioxidant activity of the membrane

[0063] Membranes (4, 8, 12, 16, 20, and 24 mg) were immersed in 4 mL of DPPH (150 μmol / L) reagent, shaken to mix, and allowed to stand in the dark for 30 minutes to allow the free radical scavenging reaction to occur fully. The absorbance was measured at 517 nm using a visible spectrophotometer (VIS-7220N, Rayleigh Analytical Instruments). For time-dependent experiments, a 20 mg membrane was immersed in 4 mL of DPPH solution, and the absorbance of the solution was measured at 10, 20, 30, 40, 50, and 60 min.

[0064] 7. Determination of the antibacterial activity of the membrane

[0065] The antibacterial activity of the bilayer membrane against Staphylococcus aureus and Escherichia coli was determined using an agar plate assay. All membranes were sterilized under UV irradiation for 20 minutes, then cut into 2cm × 2cm pieces and placed in 6-well plates. 500 μL of sterile LB medium was added to each well, followed by 100 μL of bacterial suspension (~10⁷ CFU·mL⁻¹). The plates were incubated at 37°C with gentle shaking for 24 h under both light and dark conditions. Samples were removed at 3, 6, 9, 12, and 15 h of incubation, diluted, and then placed on agar plates to determine the number of viable cells.

[0066] 8. Membrane pH, ammonia, and acid sensitivity testing

[0067] All membranes were immersed in different pH buffer solutions for 10 minutes. The ammonia and acetic acid sensitivity test was performed by placing the membranes directly in petri dishes containing 10 mL of ammonia (20%, v / v) and acetic acid (50%, v / v) for 0–40 minutes and then recording the color changes of the membranes with a digital camera.

[0068] 9. Ability to indicate the freshness of fish fillets

[0069] Fresh fish fillets were placed in a petri dish, and the smart membrane was directly attached to the inside of the dish. The fish were stored at 4°C for 4 days. The color changes of the membrane were photographed using a digital camera, and the changes in pH and TVB-N values ​​of the fish fillets were measured.

[0070] Example 1

[0071] (1) Dissolve 0.05g curcumin and 0.5g zein in 50mL of ethanol aqueous solution, stir for 6 hours and then inject into 150mL of distilled water. Remove the ethanol with a rotary evaporator to obtain curcumin / zein nano suspension.

[0072] Then, quercetin solution (10 mL, 1 mg / mL) was added dropwise to curcumin / zein nano suspension and stirred for 10 minutes to obtain quercetin / curcumin / zein nano suspension;

[0073] Subsequently, 90 mL of quercetin / curcumin / zeatin nano suspension was added dropwise to 40 mL of chondroitin sulfate solution (2 mg / mL), stirred for a period of time, and then freeze-dried to obtain nanoparticles with a core-shell structure and uniform dispersion.

[0074] (2) Chitosan (MW=50kDa) was dissolved in 1% (v / v) acetic acid solution to prepare a solution with a mass concentration of 2g / 100mL. At 40℃, 1% nanoparticles and 30% glycerol based on the mass of chitosan were added to the chitosan solution. After stirring for 1 hour, ultrasonic degassing was performed for 15 minutes to obtain a chitosan-nanoparticle active layer coating solution.

[0075] (3) Pour the active layer coating liquid prepared in the second step into the leveled mold, and then put it in the oven to dry at 40°C for 12 hours to form a smart film.

[0076] Example 2

[0077] (1) Dissolve 0.05g curcumin and 0.5g zein in 50mL of ethanol aqueous solution, stir for 6 hours and then inject into 150mL of distilled water. Remove the ethanol with a rotary evaporator to obtain curcumin / zein nano suspension.

[0078] Then, quercetin solution (10 mL, 1 mg / mL) was added dropwise to curcumin / zein nano suspension and stirred for 10 minutes to obtain quercetin / curcumin / zein nano suspension;

[0079] Subsequently, 90 mL of quercetin / curcumin / zeatin nano suspension was added dropwise to 40 mL of chondroitin sulfate solution (2 mg / mL), stirred for a period of time, and then freeze-dried to obtain nanoparticles.

[0080] (2) Chitosan (MW=50kDa) was dissolved in 1% (v / v) acetic acid solution to prepare a solution with a mass concentration of 2g / 100mL. At 40℃, 3% nanoparticles and 30% glycerol based on the mass of chitosan were added to the chitosan solution. After stirring for 1 hour, the solution was ultrasonically degassed for 15 minutes to obtain a chitosan-nanoparticle active layer coating solution.

[0081] (3) Pour the active layer coating liquid prepared in the second step into the leveled mold, and then put it in the oven to dry at 40°C for 12 hours to form a smart film.

[0082] Example 3

[0083] (1) Dissolve 0.05g curcumin and 0.5g zein in 50mL of ethanol aqueous solution, stir for 6 hours and then inject into 150mL of distilled water. Remove the ethanol with a rotary evaporator to obtain curcumin / zein nano suspension.

[0084] Then, quercetin solution (10 mL, 1 mg / mL) was added dropwise to curcumin / zein nano suspension and stirred for 10 minutes to obtain quercetin / curcumin / zein nano suspension;

[0085] Subsequently, 90 mL of quercetin / curcumin / zeatin nano suspension was added dropwise to 40 mL of chondroitin sulfate solution (2 mg / mL), stirred for a period of time, and then freeze-dried to obtain nanoparticles.

[0086] (2) Chitosan (MW=50kDa) was dissolved in 1% (v / v) acetic acid solution to prepare a solution with a mass concentration of 2g / 100mL. At 40℃, 5% nanoparticles and 30% glycerol based on the mass of chitosan were added to the chitosan solution. After stirring for 1 hour, the solution was ultrasonically degassed for 15 minutes to obtain a chitosan-nanoparticle active layer coating solution.

[0087] (3) Pour the active layer coating liquid prepared in the second step into the leveled mold, and then put it in the oven to dry at 40°C for 12 hours to form a smart film.

[0088] Comparative Example 1

[0089] Compared with Examples 1, 2, and 3, the difference is that no nanoparticles are added, and the steps are as follows:

[0090] (1) Chitosan (MW=50kDa) was dissolved in 1% (v / v) acetic acid solution to prepare a solution with a mass concentration of 2g / 100mL. Glycerol based on 30% of the mass of chitosan was added to the chitosan solution at 55℃. After stirring for 1 hour, the solution was ultrasonically degassed for 15 minutes to obtain a chitosan coating solution.

[0091] (2) Pour the prepared active layer coating liquid into the leveled mold, and then put it into the oven to dry at 40°C for 12 hours to form a chitosan film.

[0092] The performance of the smart membranes provided in Example 1 and Examples 1-3 was tested, and the results are as follows: Figure 1 As shown, A represents the tensile strength and elongation of the control example and the embodiment, and B represents the mechanical properties compared with existing polymer films. It can be seen that the tensile strength and elongation of the smart film prepared in the embodiment are higher than those of the chitosan film in the control example, indicating that the addition of nanoparticles significantly improves the mechanical properties of the film. Among them, the tensile strength and elongation of the embodiment 2 are the highest. Furthermore, the TS value of the bilayer film with added nanoparticles is comparable to that of typical packaging plastics such as low-density polyethylene (LDPE, 45.2-58.6 MPa), showing its high potential as a packaging material.

[0093] For the comparative examples and membrane moisture barrier diagrams of each embodiment in this invention, please refer to [link / reference]. Figure 2 In the diagram, A is a schematic diagram of moisture barrier performance, B is a comparison diagram of moisture content, C is a comparison diagram of water solubility, D is a comparison diagram of swelling degree, and E is a comparison diagram of water vapor transmission rate.

[0094] Depend on Figure 2 It was found that the membrane incorporating nanoparticles significantly improved the water barrier properties of the control. This phenomenon is attributed to the hydrogen-bonded interaction between the nanoparticles and the chitosan matrix, which occupies the hydroxyl groups of the chitosan molecules and blocks the binding of water molecules. Furthermore, the addition of nanoparticles reduced the water vapor transmission rate of the membrane during the water vapor transmission rate measurement experiment. These results indicate that films incorporating nanoparticles are potential food preservation and moisture-proof packaging materials, and optimizing the concentration of nanoparticles can improve the water-blocking performance of the film.

[0095] Comparative Example 2

[0096] Table 1 shows the test results of the colorimetric values, opacity, and appearance of the films in the control examples and each embodiment.

[0097] Table 1

[0098]

[0099] As can be seen from Table 1, all bilayer membrane surfaces are smooth and uniform; after the addition of nanoparticles, the ΔE of the bilayer membrane increased, mainly due to the decrease of L* and the increase of a* and b*.

[0100] Notably, the b* value exhibits greater variation and depends on the concentration effect of the nanoparticles, displaying a paler yellow hue due to the pale yellow color of the nanoparticles. Regarding opacity, the nanofilm's opacity ranges from 1.10 to 3.36, similar to the opacity value (1.67) of commercially available OPP film used for packaging. The increased nanoparticle mass ratio leads to higher opacity because the nanoparticles scatter transmitted light by occupying gaps in the polymer matrix, indicating that the presence of nanoparticles provides better food protection.

[0101] For the antioxidant activity of the membranes in the comparative examples and various embodiments, please refer to [reference needed]. Figure 3 It can be seen that, due to the increase in antioxidant content and the increase in reaction area between the reagent and the membrane, the DPPH free radical scavenging activity of all membranes is dose-dependent; the inclusion of NPs significantly enhances the antioxidant capacity of the membrane, and the antioxidant activity of the membrane increases with the increase of NPs concentration.

[0102] These results indicate that the enhanced antioxidant capacity should be attributed to the hydrogen atoms of the enol forms of curcumin and quercetin in the NPs. Furthermore, due to the slow release of active substances from the NPs membrane, the NPs membrane exhibits time-dependent DPPH radical scavenging activity; while the antioxidant activity of the amino-enhanced pure CS membrane shows a relatively stable trend. These results suggest that this nanocomposite membrane possesses high antioxidant activity and can be used in active packaging applications to prevent food oxidation, maintain food quality, and extend shelf life.

[0103] Comparative Example 3

[0104] Antibacterial activity of membranes in control examples and various embodiments:

[0105] Curcumin can effectively generate reactive oxygen species (ROS) under white light, thus exhibiting enhanced antibacterial activity; as a packaging material, the film is easily affected by light during use. Inspired by this, the antibacterial properties of the film under light and dark conditions were analyzed (see...). Figure 4 ).

[0106] It can be seen that under light irradiation, all nanocomposite films exhibited effective bactericidal effects, and the inhibitory effect increased with prolonged irradiation time. This may be because curcumin generates reactive oxygen species during light irradiation, which may cause oxidative stress, disrupting the integrity of the bacterial membrane and thus enhancing the antibacterial effect. Therefore, the nanoparticle films developed in this study have the potential to extend the shelf life of packaged foods.

[0107] For the pH sensitivity, ammonia and acid sensitivity, indication of fish freshness, changes in pH and TVB-N of fish stored at 4°C, and changes in color of fish stored at 4°C, see the comparative examples and the examples. Figure 5In the diagram, A is the pH sensitivity diagram, B is the ammonia and acid sensitivity diagram, C is the freshness indicator diagram of fish meat, D is the pH and TVB-N change diagram of fish meat stored at 4℃, and E is the color change diagram of fish meat stored at 4℃.

[0108] It can be seen that as the pH value increases from 1 to 12, the color of the NPs membrane changes from yellow (pH = 1–7) to red (pH = 8–12). This color change is mainly due to the change in the structure of the cur molecule with pH value; that is, under acidic and neutral conditions, cur mainly exists as ketones, while under alkaline conditions it exists as enols. When the NPs membrane is exposed to acidic gas for a period of time, its color changes from dark yellow to bright yellow.

[0109] In ammonia solution, the dark yellow color of the NPs membrane gradually faded to reddish-brown. The NPs membrane exhibited a significant color change within 40 minutes, indicating its high sensitivity to ammonia and acidic gases. Furthermore, the color intensity increased significantly with increasing reaction time, reaching a constant value after approximately 20 minutes. This is because the presence of volatile ammonia and acetic acid respectively created alkaline and acidic conditions within the NPs membrane, leading to a structural transformation of the cur and thus the pH-induced color change discussed earlier. Additionally, the smart membrane can be used to detect food spoilage, such as fish fillets. The color of all NPs membranes showed almost no change after 2 days of fish fillet storage, as the fillets were still fresh, consistent with the results from TVB-N. As expected, the NPs membrane underwent a significant color change after 3 days of storage, from an initial pale yellow to brownish-yellow, indicating that the fish fillets had begun to spoil. Therefore, this NPs smart membrane is suitable for monitoring the freshness of fish fillets.

[0110] Comparative Example 4

[0111] Nanoparticles were prepared according to the conditions in Example 1:

[0112] The nanoparticles prepared with 0.03g of curcumin had a size of 189nm, with a curcumin encapsulation efficiency of only 68.9% and a loading rate of 18.5%, while the quercetin encapsulation efficiency was only 69.6% and the loading rate was 17.1%.

[0113] The nanoparticles prepared with 0.04g of curcumin had a size of 215nm, with a curcumin encapsulation efficiency of only 73.2% and a loading rate of 20.3%, while the quercetin encapsulation efficiency was only 81.6% and the loading rate was 19.3%.

[0114] The nanoparticles prepared with 0.06g of curcumin had a size of 375nm, with a curcumin encapsulation efficiency of only 53.5% and a loading rate of 13.2%, while the quercetin encapsulation efficiency was only 63.6% and the loading rate was 15.1%.

[0115] It can be seen that only when the ratio of curcumin to zein is appropriate can curcumin be completely encapsulated within the nonpolar interior of zein, while the more polar quercetin is adsorbed onto chondroitin sulfate to form more uniform and stable nanoparticles.

[0116] from Figure 6 As can be seen, when the amount of curcumin added is 0.05g, the average diameter and PDI of the formed nanoparticles are 154nm and 0.26, respectively, and the zeta potential of NPs is -39.7mV, indicating that there is electrostatic repulsion between NPs, which keeps them stable.

[0117] SEM images from CZQC NPs (see) Figure 7 As can be seen, NPs are spherical with a smooth surface.

[0118] The encapsulation efficiency and loading rate of curcumin in NPs were approximately 87.3% and 25.6%, respectively, while those of quercetin were 92.6% and 29.4%, respectively.

[0119] Found in the infrared spectrum (see...) Figure 7 Compared to zein, the peaks corresponding to the hydroxyl and amide II groups in NPs shifted from 3292 and 1538 cm⁻¹ to 3407 and 1543 cm⁻¹, respectively. -1 The results indicate that there are hydrogen bonds and hydrophobic interactions between zein and curcumin. These results suggest that curcumin is encapsulated in the hydrophobic core of zein through hydrophobic interactions and hydrogen bonds, while quercetin is adsorbed onto their surfaces through electrostatic interactions and hydrogen bonds, and chondroitin sulfate is deposited on their surfaces through electrostatic interactions and hydrogen bonds.

[0120] In this invention, the stability and encapsulation efficiency of curcumin in nanoparticles are enhanced by incorporating quercetin and chondroitin sulfate, thereby improving the color development effect of the nanoparticles. This is because the more stable nanoparticle structure allows curcumin to be released more slowly.

[0121] In summary, compared with chitosan / zein bilayer membranes prepared without nanoparticles, bilayer membranes prepared with nanoparticles have better mechanical properties, moisture resistance, antioxidant capacity, antibacterial properties, and freshness indication, and are more versatile.

[0122] 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a high-toughness chitosan-based smart membrane for preserving and visually monitoring the freshness of fish, characterized in that: The method comprises the steps of: The curcumin and zein are dissolved in an ethanol solution, and after stirring, the obtained solution is injected into distilled water, and then the ethanol is removed by a rotary evaporator to obtain a curcumin / zein nanosuspension, wherein the concentration of the curcumin is 1-3 mg / mL, and the concentration of the zein is 10-15 mg / mL; The quercetin solution is added dropwise into the curcumin / zein nanosuspension, and after uniform stirring, a quercetin / curcumin / zein nanosuspension is obtained, wherein the concentration of the quercetin solution is 1-3 mg / mL, and the volume ratio of the quercetin solution to the curcumin / zein nanosuspension is 0.5-2:5; The quercetin / curcumin / zein nanosuspension is added dropwise into a chondroitin sulfate solution, and after uniform stirring, nanoparticles are obtained by freeze-drying, wherein the concentration of the chondroitin sulfate solution is 1-3 mg / mL, and the volume ratio of the quercetin / curcumin / zein nanosuspension to the chondroitin sulfate solution is 80-90:20-40; The chitosan is dissolved in acetic acid to prepare a chitosan solution, the nanoparticles and a plasticizer are added into the chitosan solution, and stirring and ultrasonic degassing are performed to obtain an active layer coating solution; The prepared coating solution is uniformly placed in a film-forming container, and dried in an oven to form an intelligent film.

2. The production method according to claim 1, characterized by: In the active layer coating solution, the mass fraction of the chitosan is 2-4%, the mass fraction of the nanoparticles in the active layer coating solution is 1-5%, and the mass fraction of the plasticizer is 25-40%.

3. The production method according to claim 1, wherein: The plasticizer is glycerol.

4. The production method according to claim 3, characterized by: In the drying to form the intelligent film, The drying temperature is 40-50 DEG C, and the drying time is 20-24 hours.

5. The high-toughness chitosan-based intelligent film with preservation and visual monitoring of fish freshness, which is prepared by the preparation method in any one of claims 1-4.

6. Use of the high-toughness chitosan-based smart membrane according to claim 5 for detecting the freshness of fish meat, characterized in that: The method comprises the steps of: Fresh fish is placed in a box with an intelligent indicating film, and stored, transported or sold at 4 DEG C; The packaging box with the intelligent indicating film is photographed, the picture information of the intelligent indicating film is recorded, and the freshness of the intelligent indicating film is determined.

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