A carbon quantum dot-polyvinyl alcohol composite film and a preparation method and application thereof

Abstract

The present application relates to the technical field of food packaging preservation material preparation, and particularly relates to a carbon quantum dot-polyvinyl alcohol composite film and a preparation method and application thereof. The carbon quantum dot-polyvinyl alcohol composite film comprises polyvinyl alcohol, a plasticizer and hesperidin carbon quantum dots. The raw materials used in the present application are degradable or easy to recycle, which significantly reduces environmental pollution. By converting waste agricultural and sideline resources into valuable carbon dots, it has important value for realizing the high value of agricultural and sideline resources. The present application studies the role of hesperidin carbon quantum dots in preservation, which has important significance for developing new preservation technology, improving food storage life and preservation quality.

Description

Technical Field

[0001] This invention relates to the field of food packaging and preservation material preparation technology, and in particular to a carbon quantum dot-polyvinyl alcohol composite film, its preparation method, and its application. Background Technology

[0002] The accelerating pace of life and changing family structures have led to a surge in consumer demand for convenience and pre-packaged foods, directly driving significant growth in the market demand for food preservation film. In daily life, many factors cause fruits and vegetables to rot and spoil after harvest, making the issue of fruit and vegetable storage and preservation increasingly prominent. With continuous socio-economic development and ongoing global environmental changes, consumers are increasingly demanding environmentally friendly and cost-effective product packaging. Traditional plastic packaging materials can no longer meet market needs. As downstream consumer markets continue to upgrade and people's environmental awareness gradually strengthens, the plastic packaging industry is developing towards green safety, multi-functionality, and biodegradability.

[0003] Film-forming agents are crucial materials in food packaging, and different agents can produce cling film with varying properties. Currently, the most common cling film materials on the market are low-density polyethylene and polyvinyl chloride, which are difficult to degrade in the natural environment. Even after prolonged burial or incineration, they still cause some environmental pollution. Therefore, providing a biodegradable film material with antibacterial properties for food preservation and storage is of great significance. Summary of the Invention

[0004] Based on the above, this invention provides a carbon quantum dot-polyvinyl alcohol composite film, its preparation method, and its applications. This invention introduces bio-derived carbon dots as a natural preservative into the preservation film, resulting in a packaging material with excellent food preservation performance, light-blocking properties, biodegradability, and low cost.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is a carbon quantum dot-polyvinyl alcohol composite film, the chemical composition of which includes polyvinyl alcohol, plasticizer and hesperidin carbon quantum dots.

[0007] The second technical solution of the present invention is a method for preparing the above-mentioned carbon quantum dot-polyvinyl alcohol composite film, comprising the following steps:

[0008] Polyvinyl alcohol and glycerol were dissolved in water, and then hesperidin carbon quantum dots were added and mixed well to form a film, thus obtaining the carbon quantum dot-polyvinyl alcohol composite film.

[0009] The third technical solution of this invention is the application of the above-mentioned carbon quantum dot-polyvinyl alcohol composite film in the preservation of fruits and vegetables.

[0010] The fourth technical solution of the present invention is a method for improving the storage stability of strawberries, which involves coating the surface of strawberries with the aforementioned carbon quantum dot-polyvinyl alcohol composite film.

[0011] The present invention discloses the following technical effects:

[0012] (1) The raw materials used in this invention are biodegradable or easily recyclable, which significantly reduces environmental pollution. By converting waste agricultural and sideline resources into valuable carbon dots, it is of great value for realizing the high-value utilization of agricultural and sideline resources.

[0013] (2) This invention studies the role of hesperidin carbon quantum dots in preservation, which is of great significance for developing new preservation technologies and improving the shelf life and preservation quality of food. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in 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.

[0015] Figure 1 These are photographs of the composite membranes prepared in Example 1 and Comparative Example 1.

[0016] Figure 2 The antioxidant properties of the composite films prepared in Example 1 and Comparative Example 1;

[0017] Figure 3 The composite membranes prepared in Example 1 and Comparative Example 1 and their antibacterial properties after being stored for four months are shown. Among them, (a) is the antibacterial curve of the composite membrane prepared in Example 1 and Comparative Example 1 against Escherichia coli, (b) is the antibacterial curve of the composite membrane prepared in Example 1 and Comparative Example 1 against Staphylococcus aureus, (c) is the antibacterial curve of the composite membrane prepared in Example 1 and Comparative Example 1 against Escherichia coli after being stored for 4 months, and (d) is the antibacterial curve of the composite membrane prepared in Example 1 and Comparative Example 1 against Staphylococcus aureus after being stored for 4 months.

[0018] Figure 4 The light blocking properties of the composite films prepared in Example 1 and Comparative Example 1 are shown; where (a) is the ultraviolet absorption spectrum and (b) is the ultraviolet transmittance.

[0019] Figure 5 The emission spectra of the composite films prepared in Example 1 and Comparative Example 1 at different excitation wavelengths;

[0020] Figure 6The elongation at break and tensile strength of the composite films prepared in Example 1 and Comparative Example 1;

[0021] Figure 7 The preservation effect of the composite film prepared in Example 1 and Comparative Example 1 on strawberries;

[0022] Figure 8 The effects of the composite films prepared in Example 1 and Comparative Example 1 on the physicochemical properties of strawberries during storage are as follows: (a) brightness L*, (b) red-green color a*, (c) yellow-blue color b*, (d) hardness, (e) weight loss rate, (f) total bacterial count, and (g) vitamin C content. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] Polyvinyl alcohol (PVA) is a safe and non-toxic polyhydroxy compound polymer material with excellent biocompatibility, chemical stability, biodegradability and film-forming properties, making it a high-quality film-forming substrate.

[0029] With the rapid growth of the global economy, improved living standards, and leaps in agricultural technology, the amount of urban and agricultural waste generated has increased dramatically. If this waste accumulates over a long period, it will cause damage to the natural environment and quietly pose a potential threat to human health. Given the severity and urgency of this problem, researchers have realized that converting waste into effective carbon sources for synthetic carbon dots is not only an innovative exploration of resource recycling but also a crucial way to address environmental challenges and safeguard human well-being.

[0030] Carbon dots (CDs), as a new class of carbon nanomaterials, range in size from 1 to 10 nm and possess unique physical, chemical, and optical properties, making them promising for a wide range of applications. Agricultural and sideline wastes are non-toxic and environmentally friendly, and are widely used renewable and recyclable materials, making them ideal carbon sources for CD synthesis. This helps reduce dependence on limited resources and promotes the rational use of resources and sustainable development. Compared to traditional carbon dot preparation methods, the process of preparing carbon dots from agricultural and sideline wastes is generally more environmentally friendly. They generate less waste and have a smaller impact on the environment. This environmentally friendly preparation method helps reduce environmental pollution and promotes the development of green chemistry and green manufacturing.

[0031] Therefore, carbon dots derived from agricultural by-products were selected as preservatives and introduced into various film-forming agents to prepare preservation films with excellent light-blocking properties, preservation properties, and high safety and biodegradability. This will enable the development of carbon dots in the field of preservation and realize the high-value utilization of agricultural by-products.

[0032] This invention utilizes traditional biomass waste—citrus peels—to transform waste into valuable resources, extending the shelf life of food. The preservation mechanism involves a composite film prepared from hesperidin carbon quantum dots, polyvinyl alcohol, and glycerol. The mixing of these three components creates intermolecular forces, improving the film's mechanical properties and protecting food from physical damage. The addition of hesperidin carbon quantum dots enhances the film's UV absorption, antioxidant properties, and antibacterial properties, while also influencing the fruit's weight loss rate and firmness, slowing moisture loss, and extending the food's shelf life. This invention develops a new packaging material for the food industry (possessing antibacterial, UV-resistant, antioxidant, and biodegradable properties).

[0033] The first aspect of the present invention provides a carbon quantum dot-polyvinyl alcohol composite film, comprising polyvinyl alcohol, plasticizer and hesperidin carbon quantum dots.

[0034] In a preferred embodiment of the present invention, the mass ratio of polyvinyl alcohol, plasticizer and hesperidin carbon quantum dots is 100:20:(0.1-2.0).

[0035] In a preferred embodiment of the present invention, the plasticizer is glycerin.

[0036] In a preferred embodiment of the present invention, the method for preparing the hesperidin carbon quantum dots includes the following steps:

[0037] Hesperidin was mixed with an organic solvent and subjected to a hydrothermal reaction to obtain a mixture; after ultrasonic treatment, it was freeze-dried to obtain the hesperidin carbon quantum dots.

[0038] In a preferred embodiment of the present invention, the mass-to-volume ratio of hesperidin to organic solvent is 1 mg: 1-4 mL; the organic solvent is anhydrous ethanol; the hydrothermal reaction temperature is 160-180°C, and the time is 6-8 h; the ultrasonic treatment conditions are: intensity 0.3 W / cm². 2 ~1.8W / cm 2 The time is 30 minutes.

[0039] In some embodiments of the present invention, the hesperidin carbon quantum dots have a size of 3-6 nm; the polyvinyl alcohol is polyvinyl alcohol 1799, which is easy to dissolve and form films, and is inexpensive and has good applicability.

[0040] A second aspect of the present invention provides a method for preparing the above-mentioned carbon quantum dot-polyvinyl alcohol composite film, comprising the following steps:

[0041] Polyvinyl alcohol and glycerol were dissolved in water, and then hesperidin carbon quantum dots were added and mixed well to form a film, thus obtaining the carbon quantum dot-polyvinyl alcohol composite film.

[0042] This invention does not impose any particular limitation on the amount of water used, but adopts the solvent dosage commonly used by those skilled in the art. The amount of water used is sufficient to fully dissolve polyvinyl alcohol and glycerin and ensure the smooth progress of subsequent film formation.

[0043] In some embodiments of the present invention, polyvinyl alcohol, glycerin and water are mixed evenly, soaked at room temperature for 30 minutes, and then stirred and dissolved at 85-95°C for 1 hour (after stirring, the steps of ultrasonication or standing to remove foam are also included); the purpose of soaking and heating is to promote the dissolution of polyvinyl alcohol.

[0044] This invention does not impose any particular limitation on the film-forming method, and employs film-forming methods commonly used by those skilled in the art, such as casting and spin coating. In some embodiments of this invention, casting is used at a temperature of 40–50°C for 8–10 hours.

[0045] The third aspect of this invention provides the application of the above-mentioned carbon quantum dot-polyvinyl alcohol composite film in the preservation of fruits and vegetables.

[0046] The fourth aspect of the present invention provides a method for improving the storage stability of strawberries, wherein the above-mentioned carbon quantum dot-polyvinyl alcohol composite film is used to coat the surface of the strawberries.

[0047] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0048] The polyvinyl alcohol used in this embodiment of the invention is polyvinyl alcohol 1799; the hesperidin powder used is pure hesperidin powder extracted from traditional biomass waste—citrus peel—using a commonly used industry method, with a concentration of 95% or higher. The hesperidin extraction method is as follows: Citrus peel is dried in a 60℃ oven, ground into powder, passed through a 100-mesh sieve, and stored in a desiccator. Extraction is performed under the following conditions: methanol volume fraction of 100%, solid-liquid ratio of 1:30 (g / mL), ultrasonic time of 50 min, and ultrasonic temperature of 45℃. After centrifugation to remove the precipitate, 1.0 mL of the supernatant is filtered through a 0.22 μm filter membrane to obtain the extract. The extract is separated by preparative high-performance liquid chromatography (HPLC) under the following chromatographic conditions: using an Innoval ODS-2 preparative column (10 mm × 150 mm, 5 μm) as the stationary phase and 20% acetonitrile as the mobile phase, isocratic elution is performed. The flow rate is 3 mL / min, the column temperature is 25℃, and the injection volume is 1 mL. The eluent was collected at 16 and 18 min respectively, and the eluent was analyzed by HPLC to achieve the separation and purification from crude flavonoids to hesperidin. Reference [1] Gao Zexin, Bai Yunxi, Xie Shuting, et al. Optimization of extraction of flavonoids from citrus peel and its antioxidant activity by response surface methodology [J / OL]. Chinese Journal of Hemp Industry, 1-17 [2025-0823].

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] Step 1: Accurately weigh 15 mg of hesperidin and 50 mL of anhydrous ethanol, place them in a high-temperature reaction vessel for hydrothermal reaction, react at 180 °C for 6 h, cool to room temperature, remove, and obtain a hesperidin carbon dot mixture.

[0052] Step 2: The mixture was sonicated for 30 min, and excess alcohol solution was removed by rotary evaporation; then, it was freeze-dried to obtain hesperidin carbon quantum dots (denoted as CDs) with a particle size of 4.2±0.6 nm.

[0053] Step 3: Mix polyvinyl alcohol (PVA), glycerol, and water evenly, soak at room temperature for 30 minutes, then stir and dissolve at 95°C for 1 hour to obtain a film-forming solution. Add the aforementioned hesperidin carbon quantum dots to the film-forming solution and stir at room temperature until homogeneous. Degas using ultrasonication, pour into a film-forming apparatus, and dry at room temperature to form a film, obtaining a carbon quantum dot-polyvinyl alcohol composite film, denoted as 1.5% CDs / PVA. By mass percentage, the film-forming solution contains 7.5% polyvinyl alcohol, 1.5% glycerol, 0.1125% hesperidin carbon quantum dots (hesperidin carbon quantum dots account for 1.5% of the mass of polyvinyl alcohol), with the remainder being water.

[0054] Based on Example 1, the content of hesperidin carbon quantum dots in step 3 was adjusted. The only difference from Example 1 is that the amount of hesperidin carbon quantum dots added in step 3 was adjusted to 0.0075%, 0.0375%, 0.0750%, and 0.15% of the mass of the film-forming solution. The mass of hesperidin carbon quantum dots accounted for 0.1%, 0.5%, 1.0%, and 2.0% of the mass of polyvinyl alcohol, respectively. Therefore, the composite films prepared were labeled as 0.1% CDs / PVA, 0.5% CDs / PVA, 1.0% CDs / PVA, and 2.0% CDs / PVA.

[0055] Comparative Example 1

[0056] The only difference from Example 1 is that steps 1 and 2 are omitted, and the addition of hesperidin carbon quantum dots in step 3 is also omitted. The resulting composite film is denoted as PVA.

[0057] Figure 1 These are photographs of the composite membranes prepared in Example 1 and Comparative Example 1; Figure 1 It can be seen that the prepared film surface is smooth and flat, without any obvious protruding particles. In addition, no bubbles are generated on the surface of the PVA film after adding carbon dots. As the carbon dot concentration gradually increases, the color of the composite film also gradually deepens.

[0058] Comparative Example 2

[0059] The only difference from Example 1 is that hesperidin in step 1 is replaced with an equal amount of peanut shells; all other steps and parameters are the same as in Example 1; the resulting composite membrane is denoted as P-CDs / PVA.

[0060] The performance of the carbon quantum dot-polyvinyl alcohol composite films prepared in Example 1 and Comparative Examples 1-2 was tested, and the specific process is as follows:

[0061] I. Antioxidant properties of CDs / PVA composite films

[0062] Preparation of thin film solution: Take 0.2g of the composite membrane prepared in the comparative example and the example, immerse it in 4mL of water, and soak for 24h to obtain the thin film solution.

[0063] 1. DPPH free radical scavenging rate: Add 2 mL of 0.1 mmol / L DPPH solution to 2 mL of the membrane solution, mix well, and place in the dark for half an hour. Then, measure the absorbance at 517 nm using a microplate reader. The DPPH scavenging rate is calculated using the following formula:

[0064] DPPH clearance rate (%) = (1 - A1 / A0) × 100%

[0065] Where A0 is the absorbance of the ethanol and DPPH mixture, and A1 is the absorbance of the sample and the DPPH mixture.

[0066] 2. ABTS Free Radical Scavenging Rate: Preparation of ABTS Working Solution: Weigh 38.4 mg of ABTS powder and add water to a final volume of 10 mL. Weigh 13.4 mg of potassium persulfate and add water to a final volume of 10 mL. Mix the ABTS solution and potassium persulfate solution thoroughly at a 1:1 ratio and react in the dark for 12 h. Dilute the ABTS working solution until the stable absorbance at 734 nm is 0.70 ± 0.01. Mix 0.5 mL of the film solution with 2.0 mL of the ABTS working solution thoroughly. Let stand at room temperature for 6 minutes, and immediately measure the absorbance at 734 nm.

[0067] ABTS radical scavenging rate (%) = 1 - (A1 - A2) / A0 × 100%

[0068] Wherein, A0 is the absorbance of ABTS working solution without sample, serving as the blank group; A1 is the absorbance of sample mixed with ABTS working solution; and A2 is the absorbance of sample mixed with water, serving as the control group.

[0069] The results are as follows Figure 2 As shown, the pure PVA membrane exhibits a low free radical scavenging rate. When the CDs / PVA ratio is 2.0%, the composite membrane demonstrates the highest scavenging rate for DPPH free radicals, reaching 80.21%. However, when the CDs / PVA ratio is 1.5%, the composite membrane achieves a scavenging rate of 99.14% for ABTS free radicals, showing no significant difference from the 2.0% ratio (p>0.05), indicating that the 1.5% CDs / PVA membrane exhibits the highest scavenging rate for ABTS free radicals. Therefore, the addition of CDs significantly enhances the free radical scavenging effect, giving the composite membrane strong antioxidant activity.

[0070] II. Antibacterial properties of CDs / PVA composite membrane

[0071] The tested bacteria, *Escherichia coli* and *Staphylococcus aureus*, were subjected to streaking, activation, culture, washing, and dilution to obtain OD values. 600 =0.5 (approximately 1.0 × 10⁻⁶) 7-1.0×10 8 The bacterial suspension (CFU / mL) was prepared, and then the film solution was mixed with the bacterial suspension and the culture medium solution at a ratio of 1:1:1 (volume ratio) and cultured in a shaker at 37°C. Samples were taken and measured every 2 hours.

[0072] The results are as follows Figure 3 As shown, pure PVA membranes exhibit weak inhibitory effects against Escherichia coli and Staphylococcus aureus. However, with the increase of the CDs ratio in the CDs / PVA mixture, the inhibitory effect on Escherichia coli and Staphylococcus aureus continuously strengthens, indicating that carbon dots possess good antibacterial activity, thereby increasing the antibacterial properties of the membrane. Furthermore, the membrane retains antibacterial activity even after four months of storage, demonstrating the long-lasting antibacterial properties of the CDs / PVA composite membrane.

[0073] III. Light Barrier Properties of CDs / PVA Composite Films

[0074] The film was cut into strips of 10*40mm, and the ultraviolet absorption spectrum of 200-600nm was recorded using an ultraviolet spectrophotometer.

[0075] The results are as follows Figure 4 As shown in Figure (a), the absorbance of the composite film in the 200–600 nm wavelength range increases with increasing CDs concentration. Since CDs exhibit strong UV absorption near 285 nm, the composite film with PVA doping shows an absorption peak near 285 nm. Figure (b) shows that the PVA film has the highest UV transmittance in the entire UV region (200–400 nm), with T400 nm = 82.8%. With increasing CDs concentration, the UV transmittance of the composite film gradually decreases in the 200–600 nm range. The maximum transmittance of the 0.1%, 0.5%, 1.0%, 1.5%, and 2% CDs / PVA composite films in the entire UV region decreases to 81.7%, 71.3%, 59.6%, 50.9%, and 44.7%, respectively, indicating that the composite film (2.0%) can effectively absorb UV light, with a maximum UV blocking rate of 55.3%.

[0076] IV. Emission spectra of CDs / PVA composite films at different excitation wavelengths

[0077] The film was cut into strips of 10*40mm and its emission spectrum was measured and recorded using a fluorescence spectrophotometer.

[0078] The results are as follows Figure 5 As shown, each thin film exhibits excitation dependence; as the excitation wavelength changes, the emission peak of the thin film gradually redshifts.

[0079] V. Mechanical Properties of CDs / PVA Composite Films

[0080] According to GB / T1040.3-2006, the mechanical properties of the film were tested. The film was cut into strips with a length of 4 cm and a width of 1 cm. The film was tested in a constant temperature and humidity environment using a universal mechanical testing machine at a tensile speed of 200 mm / min. Each sample was measured 6 times and the average value was taken.

[0081] The results are as follows Figure 6 As shown, with the increase of CDs in CDs / PVA, the tensile strength increases continuously, while the elongation at break increases first and then decreases slightly.

[0082] VI. Conduct preservation performance tests

[0083] Fresh strawberries of uniform size, shape, and color with no surface damage were purchased from the market and placed in paper cups covered with a film for preservation. The strawberries were divided into four groups: a control group without film, a PVA group, a commercial PE preservation film group, and a 1.5% CDs / PVA group. The strawberries were stored at 25°C for 5 days, and the changes in the strawberries were recorded by taking photos. Samples were taken daily for testing and analysis, and the firmness, weight loss rate, color difference, total bacterial count, and vitamin C content of the strawberries were measured.

[0084] (1) Changes in the firmness of strawberries during storage

[0085] The firmness of strawberries was determined using a texture analyzer. The testing speed was 60 mm / min, the trigger force was 0.049 N, the puncture distance was 10 mm, and six replicates were performed for each treatment group.

[0086] (2) Weight loss rate of strawberries during storage

[0087] The weight loss rate of strawberries was calculated by dividing the weight loss at sampling time by the initial weight, with six replicates for each treatment group.

[0088] (3) Color changes of strawberries during storage

[0089] The color difference (L*, a*, b*) of strawberries was measured using a colorimeter.

[0090] (4) Changes in total bacterial count of strawberries during storage

[0091] Referencing the food microbiology testing standard GB4789.2-2016 for total bacterial count determination, the specific procedure is as follows: Weigh 25g of strawberries, add 225mL of phosphate buffer solution, homogenize mechanically, and then perform a 10-fold serial dilution. Select appropriate sample homogenates, take 1mL of each homogenate, and add it to a sterile petri dish. Then add approximately 20mL of plate counting agar medium, mix well, and incubate at 37℃ for 24-48 hours. Calculate the colony count on each plate.

[0092] (5) Changes in vitamin C content of strawberries during storage

[0093] Using Fe 3+ It reacts rapidly with reduced ascorbic acid to form Fe 2+ Fe 2+ The principle of colorimetric reaction with phenoxyline is used to determine the vitamin C content in strawberries.

[0094] The results are as follows Figure 7 , Figure 8 As shown, compared with pure PVA film, CDs / PVA film has a positive effect on maintaining the brightness of strawberries, and can slow down the degree of color difference change to a certain extent. CDs / PVA film can maintain the firmness of strawberries, effectively delay the softening of strawberries during storage, slow down the decrease in weight loss rate during storage, delay the proliferation of microorganisms during storage, and effectively delay the decrease in vitamin C content.

[0095] VII. Preservation Performance of P-CDs on Strawberries: The preservation experiment was conducted according to Section VI, "Preservation Performance Test," using a P-CDs / PVA composite film. Table 1 shows that strawberries began to rot on the third day. The control group showed the highest rot rate, indicating that the P-CDs / PVA composite film did not effectively slow down the rot. The 1.5% CDs / PVA composite film resulted in the lowest rot rate. Tables 2-3 show that the P-CDs / PVA composite film was ineffective in maintaining strawberry firmness and reducing weight loss. The 1.5% CDs / PVA film maintained strawberry firmness, effectively delaying softening during storage and reducing weight loss.

[0096] Table 1 shows the effect of the composite films prepared in Example 1 and Comparative Example 2 on the strawberry rot rate:

[0097] Table 1

[0098] Storage time (d) Control 1.5% CDs / PVA P-CDs / PVA 0 0.00％ 0.00％ 0.00％ 1 0.00％ 0.00％ 0.00％ 2 0.00％ 0.00％ 0.00％ 3 38.89±5.56％ 0.00％ 29.63±3.20％ 4 55.56±5.56％ 0.00％ 53.71±3.21 5 77.77±5.56％ 9.26％±3.20％ 72.22±5.55％

[0099] Table 2 shows the effect of the composite films prepared in Example 1 and Comparative Example 2 on the firmness of strawberries:

[0100] Table 2

[0101]

[0102]

[0103] Table 3 shows the effect of the composite membranes prepared in Example 1 and Comparative Example 2 on the weight loss rate of strawberries:

[0104] Table 3

[0105] Storage time (d) Control 1.5% CDs / PVA P-CDs / PVA 0 0.00％ 0.00％ 0.00％ 1 4.11％±1.16％ 1.06％±0.55％ 2.33％±1.15％ 2 12.46％±1.32％ 2.20％±0.58％ 5.33％±1.53％ 3 15.15％±2.54％ 2.93％±0.67％ 8.77％±1.37％ 4 19.97％±2.98％ 4.87％±0.45％ 9.73％±1.62％ 5 23.93％±1.75％ 6.15％±0.66％ 10.33％±1.53％

[0106] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A carbon quantum dot-polyvinyl alcohol composite film, characterized in that, Its chemical composition includes polyvinyl alcohol, plasticizers, and hesperidin carbon quantum dots; The mass ratio of polyvinyl alcohol, plasticizer, and hesperidin carbon quantum dots is 100:20:(0.1~2.0).

2. The carbon quantum dot-polyvinyl alcohol composite film according to claim 1, characterized in that, The plasticizer is glycerin.

3. The carbon quantum dot-polyvinyl alcohol composite film according to claim 1, characterized in that, The preparation method of the hesperidin carbon quantum dots includes the following steps: Hesperidin was mixed with an organic solvent and subjected to a hydrothermal reaction to obtain a mixture; after ultrasonic treatment, it was freeze-dried to obtain the hesperidin carbon quantum dots.

4. The carbon quantum dot-polyvinyl alcohol composite film according to claim 3, characterized in that, The mass-to-volume ratio of hesperidin to organic solvent is 1 mg: 1~4 mL; the organic solvent is anhydrous ethanol; the hydrothermal reaction temperature is 160~180℃, and the time is 6~8 h; the ultrasonic treatment conditions are: intensity 0.3 W / cm²~1.8 W / cm², and time 30 min.

5. A method for preparing a carbon quantum dot-polyvinyl alcohol composite film according to any one of claims 1 to 4, characterized in that, Includes the following steps: Polyvinyl alcohol and glycerol were dissolved in water, and then hesperidin carbon quantum dots were added and mixed well to form a film, thus obtaining the carbon quantum dot-polyvinyl alcohol composite film.

6. The application of the carbon quantum dot-polyvinyl alcohol composite film as described in any one of claims 1 to 4 in the preservation of fruits and vegetables.

7. A method for improving the storage stability of strawberries, characterized in that, The carbon quantum dot-polyvinyl alcohol composite film according to any one of claims 1 to 4 is used to coat the surface of strawberries.

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