Quantum dot E / NPER-CDs, preparation method thereof and application in food preservation

Abstract

The present invention discloses a quantum dot E / NPER‑CDs, a preparation method thereof and an application in food preservation, and belongs to the technical field of food preservation. The quantum dot E / NPER‑CDs described in the present invention are prepared by the following method: adding oyster mushroom root powder, EDTA‑Na2 and citric acid to water, reacting at high temperature, centrifuging after the reaction is completed, taking the supernatant for dialysis, and then freeze-drying the dialysate to obtain quantum dot E / NPER‑CDs. The quantum dot E / NPER‑CDs has significant in vitro antioxidant capacity and has a good inhibitory effect on Escherichia coli and Staphylococcus aureus. The chitosan coating liquid prepared from quantum dot E / NPER‑CDs can significantly inhibit ROS (O2 ·‑ and H2O2), delaying the degradation of total phenols, ascorbic acid (AsA), and glutathione (GSH), while significantly reducing the activities of SOD, CAT, POD, APX, and PPO, and delaying the peaks of SOD, CAT, POD, and APX, so as to achieve the effect of improving the quality of fresh-cut pears during storage, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of food preservation, and in particular relates to quantum dots E / NPER-CDs, a preparation method thereof and application in food preservation. Background Art

[0002] Fresh-cut fruits and vegetables, also known as lightly processed or semi-processed fruits and vegetables, are fresh fruits and vegetables that have undergone a series of processing steps, including washing, cutting, packaging, and preservation, resulting in a convenient, safe, and fresh, ready-to-eat product for consumers. Fresh-cut fruits and vegetables are popular for their freshness, portability, and ready-to-eat nature, and their consumption is growing in the overall fruit and vegetable market.

[0003] Although fresh-cut fruits and vegetables are minimally processed products, during their processing, the fruits still need to be washed, peeled, cored, cut, and other processes. The unit operations used in these processes will destroy the surface cells and stress tissues of the fruit, exposing the cytoplasm and providing microorganisms with more nutrients than the whole fruit. At the same time, fruits and vegetables may be contaminated by microorganisms in various links such as planting, harvesting, processing, storage, transportation, and sales. Therefore, microbial infection has become the primary issue worthy of attention during the processing of fresh-cut fruit and vegetable products. Microbial infection will not only shorten the shelf life of fresh-cut fruit and vegetable products and affect sales, but also cause foodborne diseases and pose a risk to consumers' health. Hu et al. (2018) found that the total number of microorganisms in fresh-cut apples reached 6log CFU g after 8 days of refrigeration. -1 , which has exceeded the microbial safety level of fresh-cut fruits and vegetables. Azarakhsh et al. (2014) reached a similar conclusion in a fresh-cut pineapple preservation experiment. The total number of microorganisms, yeasts and molds in fresh-cut pineapples exceeded 6 log CFU g after 8 days of storage. -1 , and after 12 days of storage, it was close to 8 log CFU g -1 Pineapples experienced severe spoilage. Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus have become important pathogens of foodborne illness associated with fresh-cut produce in food poisoning incidents reported in various countries (Feng Ke et al., 2018; Vandamm et al., 2013).

[0004] At the same time, damage to the fruit causes increased respiration and ethylene production, ultimately leading to a rapid decline in fruit quality over a short period of time, ultimately causing the fruit to lose its commercial properties. Therefore, it is of great significance to develop an environmentally friendly, edible nanocomposite coating with antioxidant and antibacterial properties to address the aforementioned preservation issues of fresh-cut fruits and vegetables, address the microbial safety of fresh-cut fruits and vegetables, and thus extend the shelf life of the products. Summary of the Invention

[0005] The present invention provides a method for preparing quantum dot E / NPER-CDs, comprising the following steps:

[0006] Pleurotus eryngii root powder, EDTA-Na2 and citric acid were added to water and reacted at high temperature. After the reaction was completed, the mixture was centrifuged, the supernatant was dialyzed, and the dialyzate was freeze-dried to obtain quantum dots E / NPER-CDs.

[0007] In the above preparation method, the mass ratio of the Pleurotus eryngii root powder, EDTA-Na2 and citric acid is selected from 4-6:1-3:1-3; preferably 5:2:2.

[0008] In the above preparation method, the mass volume ratio of the Pleurotus eryngii root powder to water is selected from 1:40 to 64, g / mL; preferably 1:48, g / mL.

[0009] In the above preparation method, the high temperature reaction conditions are selected from: treating at 140-200° C. for 2-10 h; preferably reacting at 180° C. for 8 h.

[0010] The present invention provides quantum dots E / NPER-CDs prepared by the above method.

[0011] The present invention provides the use of the quantum dots E / NPER-CDs in food anti-oxidation and / or antibacterial properties; the bacteria are selected from Escherichia coli and / or Staphylococcus aureus.

[0012] The present invention provides the use of the quantum dot E / NPER-CDs in preparing antioxidant and / or antibacterial preparations.

[0013] The present invention provides the use of the quantum dot E / NPER-CDs in food preservation; the food is selected from fresh-cut fruits and vegetables.

[0014] The invention provides a chitosan / quantum dot coating liquid, which is prepared by the following method: mixing a quantum dot E / NPER-CDs solution with a chitosan solution, and stirring the mixture to obtain the chitosan / quantum dot coating liquid.

[0015] In the present invention, the concentration of the chitosan solution is selected from 0.8 to 1.2%, preferably 1%.

[0016] In the present invention, the concentration of the quantum dot E / NPER-CDs solution is selected from 80 to 120 mg / mL, preferably 100 mg / mL.

[0017] In the present invention, the chitosan solution is an acetic acid solution of chitosan; and the quantum dot E / NPER-CDs solution is an aqueous solution of quantum dots E / NPER-CDs.

[0018] The present invention provides application of the chitosan / quantum dot coating liquid in preserving fresh-cut fruits and vegetables.

[0019] The beneficial effects of the present invention are:

[0020] The present invention uses Pleurotus eryngii root powder, EDTA-Na2 and citric acid to prepare a quantum dot E / NPER-CDs, which has significant in vitro antioxidant capacity and has a good inhibitory effect on Escherichia coli and Staphylococcus aureus. The chitosan coating liquid prepared from quantum dot E / NPER-CDs can significantly inhibit ROS (O2 ·- and H2O2), delaying the degradation of total phenols, ascorbic acid (AsA), and glutathione (GSH), while significantly reducing the activities of SOD, CAT, POD, APX, and PPO, and delaying the peaks of SOD, CAT, POD, and APX, so as to achieve the effect of improving the quality of fresh-cut pears during storage, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 TEM images of three quantum dots;

[0022] Figure 2 FT-IR spectra of three quantum dots;

[0023] Figure 3 The scavenging ability of the three carbon quantum dots on DPPH, hydroxyl radicals and superoxide anions;

[0024] Figure 4 The inhibition rates of carbon quantum dots at different concentrations on Escherichia coli (a) and Staphylococcus aureus (b);

[0025] Figure 5 The inhibitory effects of different carbon quantum dots on Escherichia coli and Staphylococcus aureus;

[0026] Figure 6 Scanning electron microscope images of Escherichia coli and Staphylococcus aureus after treatment with different carbon quantum dots;

[0027] Figure 7 The effect of different quantum dot coating solutions on the total bacterial count on the surface of fresh-cut pear pulp tissue;

[0028] Figure 8 The effect of different quantum dot coating solutions on the antioxidant content of fresh-cut pears; a is the total phenol content, b is the ascorbic acid content, and c is the glutathione content;

[0029] Figure 9 Effects of different quantum dot coating solutions on H2O2 and O2 in fresh-cut pears ·- The influence of content;

[0030] Figure 10 The activities of ROS metabolism-related enzymes in fresh-cut pears treated with different quantum dot coating solutions; a is SOD, b is CAT, c is POD, d is APX, and e is PPO. DETAILED DESCRIPTION

[0031] King oyster mushroom (Pleurotus eryngii), also known as Pleurotus eryngii, belongs to the Basidiomycota, Basidiomycetes, Asteraceae, Agaricales, Pleurotus family, and genus Pleurotus. It is a dual-purpose edible mushroom with extremely high nutritional and medicinal value. King oyster mushrooms are nutritious, delicious, and have an almond-like aroma. They are high in protein and low in fat, and contain eight essential amino acids, as well as a wealth of dietary fiber and minerals. They are a typical high-potassium, low-sodium health food. Modern pharmacological research has shown that king oyster mushrooms are effective in boosting immunity, preventing cancer and cardiovascular and cerebrovascular diseases, and improving gastrointestinal function, making them a popular choice among consumers.

[0032] King oyster mushrooms contain a variety of active substances, among which polysaccharides have been shown to exhibit diverse biological activities, including hypoglycemic (Chen et al., 2016), anti-tumor (Ma et al., 2014), antioxidant (Li et al., 2016), lipid-lowering (Chen et al., 2016), and anti-inflammatory (Chen et al., 2016). King oyster mushrooms are also easy to cultivate and have high yields, leading to their widespread cultivation worldwide.

[0033] With the continuous improvement of King Oyster Mushroom production capacity and the rapid development of factory production, a large number of King Oyster Mushroom by-products are also produced as its output expands, such as the culture medium discarded after King Oyster Mushroom is picked, the large number of mushroom feet and mushroom roots that are uniformly removed during the bud thinning process and the packaging process to ensure the quality of fresh King Oyster Mushrooms. Among them, the cut mushroom buds, mushroom feet, mushroom roots and other by-products account for about 20% to 25% of the King Oyster Mushroom production. These by-products have the characteristics of large output and easy collection. At the same time, these by-products have the same rich nutritional components and similar texture as commercial mushrooms. According to the report of Jiang Huiyan et al. (2018), the main nutrients of King Oyster Mushroom by-products are carbohydrates (54.2%), protein

[0034] The carbohydrate (17.3%), crude fat (1.74%), and ash (6.63%) contents of King Oyster Mushrooms were not significantly different from those of commercial mushrooms, including carbohydrates (51.9%), protein (20.11%), crude fat (2.19%), and ash (6.15%). However, cultivation companies primarily focus on the primary processing of King Oyster Mushroom products, with lagging behind in deep processing technology and R&D capabilities. Due to their poor uniformity and low commercial value, these high-quality King Oyster Mushroom by-products are often processed at low prices or directly discarded as waste, wasting a huge amount of resources and causing environmental pollution if not handled properly.

[0035] On this basis, the present invention is dedicated to applying King Oyster Mushroom by-products to the field of food preservation.

[0036] The materials used in the present invention are as follows:

[0037] King oyster mushroom by-products were purchased from the fruit wholesale market in Chengyang District, Qingdao City. The purchased king oyster mushroom by-products were sliced ​​and freeze-dried using a vacuum freeze dryer. The freeze-dried dry product was ground into powder using a high-throughput tissue grinder and sieved for later use.

[0038] Crown pears were purchased from the Chengyang Fruit and Vegetable Wholesale Market in Qingdao. Uniformly sized, undamaged pears were selected for the experiments. All pears were pre-cooled at 4°C for 24 hours in a cold storage facility at the Qingdao Agricultural University Teaching and Training Base.

[0039] An HT-7700 transmission electron microscope was purchased from Hitachi, Japan; a Nano ZS90 nanoparticle size analyzer was purchased from Malvern Instruments Ltd., UK; a Nicolet is10 Fourier transform infrared spectrometer was purchased from Thermo Fisher Scientific Inc., USA; an F-2700 fluorescence spectrophotometer was purchased from Hitachi, Japan; a D8ADVANCE X-ray polycrystal diffractometer was purchased from Bruker AG, Germany; a SpectraMax i3x microplate reader was purchased from Meigu Molecular Instruments (Shanghai) Co., Ltd.; a JSM7500F scanning electron microscope was purchased from JEOL Ltd.; a UV-visible spectrophotometer was purchased from Shanghai Uniqlo Co., Ltd.; an H3-16KR desktop high-speed refrigerated centrifuge was purchased from Hunan Kecheng Instrument Equipment Co., Ltd.; a research-grade upright fluorescence microscope was purchased from Olympus (China) Co., Ltd.; an electronic balance was purchased from Ohaus Instruments (Changzhou) Co., Ltd.; and EDTA-Na2 and citric acid were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0040] In the present invention, Origin 2023b was used for drawing, and IBM SPSS Statistics 26 was used for one-way analysis of variance and significance analysis, and P < 0.05 indicated significant differences.

[0041] The other materials used in the present invention, unless otherwise stated, can be obtained through commercial channels. Unless otherwise specified, other terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art. The present invention will be further described in detail below with reference to specific examples and data. The following examples are merely for illustration of the present invention and are not intended to limit the scope of the present invention in any way.

[0042] Example 1

[0043] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0044] 1.25 g of Pleurotus eryngii root powder, 0.5 g of EDTA-Na₂, and 0.5 g of citric acid were mixed with 60 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0045] Comparative Example 1

[0046] The steps for preparing quantum dot PER-CDs are as follows:

[0047] Mix 1.25 g of Pleurotus eryngii root powder with 60 mL of ultrapure water, and transfer the mixture to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture is then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product is centrifuged at 10,000 g, and the supernatant is collected and filtered through a 0.22 µm filter. The filtrate is purified by dialysis with a 500 Da molecular weight cutoff for 48 h. The dialyzate is lyophilized to obtain PER-CDs powder. The powder is stored in a desiccator to prevent moisture absorption.

[0048] Comparative Example 2

[0049] The steps for preparing quantum dot EPER-CDs are as follows:

[0050] 1.25 g of Pleurotus eryngii root powder, 0.5 g of EDTA-Na₂, and 60 mL of ultrapure water were mixed and transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain EPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0051] 1. Characterization of Carbon Quantum Dots

[0052] 1. Transmission electron microscopy imaging analysis

[0053] 10 mg of each lyophilized quantum dot powder was dissolved in 5 mL of deionized water. The 2 mg / mL aqueous solution of quantum dots was then sonicated for 10 minutes. Using a pipette, 10 mL of the aqueous solution was dripped onto a carbon-coated copper grid and then heated under an infrared lamp for 30 minutes until thoroughly dry. This process was repeated three times. TEM images of the quantum dots were obtained using a transmission electron microscope (HT-7700) at 80 kV.

[0054] The test results are as follows Figure 1 As shown:

[0055] The prepared quantum dots E / NPER-CDs are well-dispersed and evenly distributed spherical particles with a particle size of less than 10 nm, which is within the typical particle size range of carbon quantum dots.

[0056] 2. Nanoparticle size and Zeta potential analysis

[0057] Dissolve 20 mg of each lyophilized quantum dot powder in 20 mL of ultrapure water. The resulting 1 mg / mL aqueous solution was filtered through a 0.22 μm pore size filter. The particle size and zeta potential of the quantum dots were measured using a Nano ZS90 nanometer particle size analyzer equipped with a dedicated DTS0012 sample cell and a DST1070 Zeta potential sample cell.

[0058] The test results are shown in Table 1:

[0059] Table 1 Nanoparticle size and zeta potential of different CDs

[0060]

[0061] As shown in Table 1, the average particle sizes of PER-CDs, EPER-CDs, and E / NPER-CDs are 2.89 nm, 3.27 nm, and 6.4 nm, respectively. All carbon quantum dots are smaller than 10 nm, falling within the typical particle size distribution of CDs. The particle sizes of EPER-CDs and E / NPER-CDs synthesized by doping are significantly larger than those of PER-CDs (P < 0.05). This may be due to the richer surface functional groups of EPER-CDs and E / NPER-CDs.

[0062] The zeta potential of nanoparticles reflects the surface charge density of the particles and can be used to indicate the stability of nanoparticle solutions. Generally, a higher zeta potential indicates a more stable nanoparticle solution. The zeta value also indicates the potential for interaction between CDs and bacteria. Table 1 shows that the zeta potential of PER-CDs is -14.63 mV. After doping with EDTA-Na₂, the zeta potential decreases to -20.17 mV, likely due to the higher electronegativity of nitrogen atoms (3.04) compared to carbon atoms (2.55). However, after doping with EDTA-Na₂ and citric acid, the zeta potential increases to -6.29 mV. This is likely due to the fact that citric acid is primarily composed of carbon atoms, which increases its zeta potential.

[0063] 3. Fourier transform infrared spectroscopy analysis

[0064] 10 mg of each quantum dot powder was mixed evenly with 200 mg of potassium bromide (KBr) powder and then pressed into a tablet using a tableting mold. The FT-IR spectrum was measured using an iS10 Fourier transform infrared spectrometer in the spectral range of 4000-400 cm -1 .

[0065] The test results are as follows Figure 2 As shown:

[0066] The particle size distribution and zeta potential of the three carbon quantum dots are significantly different, which may be due to the different types of surface functional groups. Therefore, FT-IR spectroscopy was used to analyze the surface functional groups of the three carbon quantum dots. Figure 2 It can be seen that the three types of carbon quantum dots exist at the same time at 3278.04 cm -1 The widest peak is 2917.92cm -1 、1591.31cm -1 、1024.97cm -1 and 1403.56cm -1 The relatively narrow peaks may correspond to the OH stretching vibration peak, CH stretching vibration peak, C=O and CO stretching vibration peak and C=C stretching bending vibration peak. Based on these peaks, it is speculated that there may be carboxyl and hydroxyl groups on the surface of the three carbon quantum dots. The presence of these functional groups makes PER-CDs, EPER-CDs and E / NPER-CDs hydrophilic and water-soluble. At the same time, due to the doping of EDTA-Na2, EPER-CDs has two more obvious peaks than PER-CDs, which are 1622cm -1 and 1400cm -1The two peaks correspond to the bending vibration of NH and the stretching vibration of CN, respectively, indicating that nitrogen has been successfully introduced into the surface of EPER-CDs in the form of amine groups. E / NPER-CDs also showed two peaks similar to those of EPER-CDs, and also showed a peak at 1200 cm -1 These results are consistent with the negative charge of carbon quantum dots obtained from zeta potential analysis.

[0067] 3. Evaluation of Antioxidant Capacity in Vitro

[0068] 1. DPPH clearance rate

[0069] 100 μL of 2 mM DPPH ethanol solution and 100 μL of 2 mg / mL quantum dot solution were added to a 96-well plate and mixed thoroughly in the dark for 30 minutes. Ethanol was used instead of the quantum dot solution and DPPH ethanol solution as blank controls. The absorbance of each mixture was measured at 517 nm using a SpectraMax i3x microplate reader. The data were recorded and repeated three times. The DPPH scavenging activity of the quantum dots was calculated using the following formula:

[0070]

[0071] Wherein, A0 is the absorbance value of the quantum dot solution sample when ethanol is used instead of the quantum dot solution sample, A1 is the absorbance value of the quantum dot solution sample, and A2 is the absorbance value of the DPPH ethanol solution when ethanol is used instead of the quantum dot solution sample.

[0072] 2. O2 ·- Clearance

[0073] 30 μL of 2 mg / mL quantum dot solution, 150 μL of 50 mmol / L Tris-HCl buffer, and 30 μL of 25 mmol / L pyrogallol solution were added to a 96-well plate and mixed. The mixture was reacted at room temperature for 5 min. Finally, 15 μL of 8 mmol / L hydrochloric acid solution was added to terminate the reaction. Tris-HCl buffer was used to replace the quantum dot solution and pyrogallol solution as blank controls. The absorbance of each mixture was measured at 320 nm using a SpectraMax i3x microplate reader. The data were recorded. The experiment was repeated 3 times. The O2 of the quantum dots was calculated using the following formula: ·- Scavenging activity:

[0074]

[0075] Wherein, A0 is the absorbance value of the quantum dot solution sample replaced by Tris-HCl buffer, A1 is the absorbance value of the quantum dot solution sample, and A2 is the absorbance value of the pyrogallol solution replaced by Tris-HCl buffer.

[0076] 3. OH

[0077] The hydroxyl radical (·OH) scavenging activity of quantum dots was determined using a Fenton-based reaction. 50 μL of a 9 mM FeSO₄ solution and 50 μL of a 9 mM ethanolic salicylic acid solution were mixed with 50 μL of a 2 mg / mL quantum dot solution. 50 μL of 9 mM H₂O₂ was then added, replacing the quantum dot solution sample and H₂O₂ with distilled water. The mixture was incubated at 37°C for 30 minutes, and the absorbance at 510 nm was measured and recorded. The experiment was repeated three times. The ·OH scavenging activity of the quantum dots was calculated using the following formula.

[0078]

[0079] Where A0 is the absorbance value of the quantum dot solution sample replaced by distilled water, A1 is the absorbance value of the quantum dot solution sample, and A2 is the absorbance value of the H2O2 solution replaced by distilled water.

[0080] The test results are as follows Figure 3 As shown:

[0081] Compared with PER-CDs, EPER-CDs and E / NPER-CDs have a higher sensitivity to ·OH, and O2 ·- The scavenging ability has been significantly improved, especially for O2 ·- The removal rates of EPER-CDs and E / NPER-CDs were increased by 30.3% and 41.82%, respectively. This result shows that EPER-CDs and E / NPER-CDs have stronger electron-donating abilities, which may be related to the introduction of more amine groups. Figure 3 It can be seen that the scavenging ability of DPPH by 2 mg / mL PER-CDs, EPER-CDs and E / NPER-CDs all reached more than 90%, and the scavenging ability of hydroxyl radicals was improved, indicating that the carboxyl and hydroxyl groups on their surfaces that can provide hydrogen atoms and thus scavenge DPPH and hydroxyl radicals still exist, and there are more active sites.

[0082] IV. Evaluation of antibacterial activity

[0083] 1. Determination of minimum inhibitory concentration (MIC) by microbroth two-fold dilution method

[0084] In order to explore the antibacterial activity of the three carbon quantum dots, the minimum inhibitory concentration (MIC) was determined using the microbroth two-fold dilution method. The method is as follows: Staphylococcus aureus and Escherichia coli were cultured in a sterile LB broth medium at 37°C for 4 hours, and the concentration was diluted to 10 6CFU / mL. Add 100μL LB broth to each well of a 96-well plate, then add 100μL of three 10mg / mL carbon quantum dot solutions to the first column of wells on the left, and then dilute the three carbon quantum dots by two times. The final carbon quantum dot concentrations in each well are 4, 2, 1, 0.5, 0.25, 0.125, and 0.06125mg / mL. Finally, add the diluted bacterial solution to each well, replace the bacterial solution with LB broth as a negative control, and replace the drug solution with the bacterial solution as a positive control. Incubate in a 37°C constant temperature incubator for 16-20h, and use a microplate reader to observe the absorbance of each well at 600nm. The final inhibition rate is calculated according to the following formula:

[0085]

[0086] Where, OD 600测 Refers to the absorbance value of the experimental group at 600nm; OD 600阳对 OD refers to the absorbance value at 600nm of the control group with bacterial solution replacing drug solution; 600阴对 Refers to the absorbance value at 600nm of the control group with LB broth instead of bacterial solution; OD 600样 Refers to the absorbance value of different carbon quantum dots at 600nm.

[0087] 2. Determination of inhibition zone and antibacterial ability

[0088] Staphylococcus aureus and Escherichia coli were used as experimental bacteria for inhibition zone determination, and the diffusion method was used to detect the inhibitory effect of three types of carbon quantum dots on the two bacteria. First, 50 μL of activated and diluted to 10 6 A bacterial suspension of 100 CFU / mL was spread on MH solid culture medium. After cooling, four 9 mm small holes with equal distances and uniform distribution were punched on the medium. 50 μL of 2 mg / mL LCDs solution was added to each well, and sterile water was used as a blank control. The culture was carried out in a constant temperature incubator at 37°C for 12 h, and the diameter of the inhibition zone was calculated using an automatic colony counter.

[0089] Dilute 300 μL to 10 6 A bacterial solution containing 100 CFU / mL of IgG was mixed with 300 μL of a 2 mg / mL CDs solution and incubated at 37°C with shaking. 50 μL of the solution was then evenly spread on the surface of a MH agar medium. The mixture was incubated at 37°C for 24 hours and its antibacterial activity was observed.

[0090] 3. Scanning electron microscopy imaging analysis of bacteria

[0091] The morphology of bacteria was evaluated by SEM. Staphylococcus aureus and Escherichia coli were activated in LB broth for 4 h and then diluted to 10 8CFU / mL, add carbon quantum dot solution and 3mL bacterial solution to a 10mL sterile centrifuge tube to make the final concentration of CDs solution 2mg / mL, and incubate in a 37℃ bacterial incubator for 12h. Centrifuge at 2500r / min for 5min, discard the supernatant, and wash three times with sterile 0.2M PBS (pH=7.4) buffer to remove the residual culture medium. Dilute the bacteria to 10 with PBS buffer. 9 CFU / mL, take 0.5mL of the suspension and fix it with 2% glutaraldehyde overnight. In a clean bench, take 50μL of the fixed bacterial suspension and drop it onto a glass slide. After it dries, wash it three times with PBS buffer, fix it with osmium phosphate for 1 hour, wash it three times with PBS buffer, and then dry it with a gradient of 30%, 50%, 70%, and 90% ethanol. Finally, fix it with anhydrous ethanol and repeat three times. Remove the glass slide and place it in a CO2 critical dryer to dry, spray it with gold, and observe it using a scanning electron microscope.

[0092] The test results are as follows Figures 4-6 And as shown in Table 2:

[0093] Table 2 Inhibition zone size of different carbon quantum dots

[0094]

[0095] Testing the minimum inhibitory concentration (MIC) of antibacterial substances against bacteria is a standard method for studying their antibacterial activity. Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) were selected as the two foodborne pathogens to test the MIC of carbon quantum dots. Figure 4 It can be seen that the three types of carbon quantum dots have different antibacterial abilities and the same type of carbon quantum dots have different inhibitory abilities against different types of bacteria. PER-CDs did not show any inhibitory effect on the two bacteria, while EPER-CDs and E / NPER-CDs had significant antibacterial activity, and the activity was positively correlated with concentration. At a concentration of 2 mg / mL, the inhibition rate of EPER-CDs against the two bacteria reached 60.66% (Staphylococcus aureus) and 56.58% (Escherichia coli), while the inhibition rate of E / NPER-CDs against the two bacteria was as high as 92.36% (Staphylococcus aureus) and 85.15% (Escherichia coli).

[0096] In order to further evaluate the antibacterial activity of carbon quantum dots, the antibacterial effect of carbon quantum dots (2 mg / mL) on Staphylococcus aureus and Escherichia coli was evaluated by the perforation diffusion method and the plate coating method, and sterile water was used as a control. Figure 4 、 Figure 5It can be seen that 2 mg / mL PER-CDs had almost no inhibitory effect on E. coli and Staphylococcus aureus, while EPER-CDs and E / NPER-CDs solutions had significant antibacterial effects on Staphylococcus aureus and E. coli. The above results show that after doping, carbon quantum dots are endowed with stronger antibacterial effects.

[0097] Scanning electron microscopy (SEM) was used to observe the morphological changes of Escherichia coli and Staphylococcus aureus after treatment with three types of quantum dots, and the antibacterial effect of carbon quantum dots was explored at the microscopic level. Figure 6 As can be seen, the morphology of untreated and PER-CD-treated Staphylococcus aureus and Escherichia coli remained unchanged, with smooth bacterial surfaces. However, the morphology of Staphylococcus aureus and Escherichia coli treated with EPER-CDs and E / NPER-CDs changed significantly compared to the original treatment. Their bacterial membranes were disrupted, with irregular cell morphology, membrane invaginations, and even membrane disruption and fragmentation. These results suggest that EPER-CDs and E / NPER-CDs can kill bacteria by disrupting their cell membranes, with E / NPER-CDs showing the greatest efficacy. This may be due to the significant role of amide bonds and amino groups on the surface of nitrogen-doped carbon quantum dots in enhancing their antibacterial properties. The protonated form of these groups generates electrostatic interactions with the phospholipids of the bacterial cell membrane, leading to membrane damage, cytoplasm leakage, and bacterial death.

[0098] Example 2

[0099] Prepare chitosan / quantum dot coating solution, the steps are as follows:

[0100] At 60°C, 1g of chitosan (90% deacetylation) was dissolved in 99mL of 1% (v / v) acetic acid to prepare a 1% (v) chitosan solution. PER-CDs, EPER-CDs, and E / NPER-CDs powders were dissolved in a 100mg / mL aqueous solution, and 2mL of this solution was added to 98mL of the chitosan solution and stirred for 10 minutes to prepare 2% (v) chitosan / quantum dot coating solutions, namely, CS / PER-CDs coating solutions, CS / EPER-CDs coating solutions, and CS / E / NPER-CDs coating solutions.

[0101] 5. Storage test of fresh-cut pears

[0102] Fresh Crown pears were peeled, cored, and cut into pieces. The pieces were then immersed in distilled water (CK), CS / PER-CDs coating solution, CS / EPER-CDs coating solution, and CS / E / NPER-CDs coating solution for 3 minutes. The soaked fresh-cut pear samples were then placed in a dry environment and dried for 10 minutes to form a uniform coating on the surface. The samples were then transferred to a fresh-keeping box and stored at 4°C for 5 days. Samples were collected and analyzed on days 0, 1, 2, 3, 4, and 5.

[0103] 1. Determination of total bacterial count during storage of fresh-cut pears

[0104] The total colony count was determined according to GB4789.2-2016 standard.

[0105] 15g of fresh-cut pear pulp tissue from different treatment groups was placed in 150mL of 0.9% saline and shaken for 3 minutes. 10-fold serial dilutions were prepared by shaking. When performing a 10-fold dilution, 1mL of the sample solution was inoculated into a plate count agar medium. The plate was then rotated to mix it evenly. Sterile saline was used instead of the dilution solution as a blank control. After incubation in a constant temperature incubator at 28°C for 48 hours, the colonies on the plate were counted. This experiment was repeated three times, and the results were expressed as log CFU g -1 .

[0106] The test results are as follows Figure 7 As shown:

[0107] The total colony count (CAC) of fresh-cut pears in all treatment groups gradually increased during storage. The CAC counts of fresh-cut pears treated with CS / EPER-CDs and CS / E / NPER-CDs were significantly lower than those of the control and CS / PER-CDs-treated samples. Notably, on day 0 of storage, the CAC counts of fresh-cut pears treated with CS / EPER-CDs and CS / E / NPER-CDs were 3.96 log CFU / g and 3.79 log CFU / g, respectively, significantly lower than the control's CAC count of 4.46 log CFU / g. By day 4 of storage, the CAC count of the control had reached 6.56 log CFU / g. A CAC count exceeding 6 log CFU / g in food is considered to exceed the food safety threshold. At the end of storage, the CAC counts of fresh-cut pears treated with CS / EPER-CDs and CS / E / NPER-CDs were 5.87 log CFU / g and 5.59 log CFU / g, respectively. The total bacterial count in the CS / E / NPER-CDs-treated group at the end of storage was significantly lower than that in the other groups. This indicates that both CS / EPER-CDs and CS / E / NPER-CDs treatments can inhibit the growth of microorganisms in fresh-cut pears during storage, with the CS / E / NPER-CDs treatment being more effective.

[0108] 2. Antioxidants in the pulp tissue of fresh-cut pears during storage

[0109] (1) Determination of ascorbic acid content

[0110] The ascorbic acid content of fresh-cut pear samples was determined using the 2,6-dichlorophenol indophenol titration method. All reagents were prepared with double-distilled water. The 2,6-dichlorophenol indophenol used was calibrated with a 0.1 mg / mL standard ascorbic acid solution before titration. 20 g of pulp sample was placed in oxalic acid (20 g / L), ground and homogenized in an ice bath, and the volume was adjusted to a 100 mL brown volumetric flask. The filtrate was collected by filtration, and 10 mL of the filtrate was titrated with the calibrated 2,6-dichlorophenol indophenol. When the solution turned slightly red and did not fade within 15 seconds, the titration end point was reached. Oxalic acid solution was used as a blank control. The titration process was controlled within 2 minutes to prevent the reduced ascorbic acid from being oxidized. The experimental data was recorded and repeated three times. The ascorbic acid content was calculated according to the following formula:

[0111]

[0112] Where, V1 is the volume of 2,6-dichlorophenol indophenol consumed in the sample titration, mL; V0 is the volume of 2,6-dichlorophenol indophenol consumed in the blank titration, mL; ρ is the content of ascorbic acid equivalent to 1 mL of 2,6-dichlorophenol indophenol, mg / mL; V sis the volume of the sample taken during titration, mL; m is the mass of the sample taken, g; V is the total volume of the sample extract, mL.

[0113] (2) Determination of total phenol content

[0114] The total phenols in fresh-cut pear samples were extracted using 1% HCl-methanol solution. 3g of fresh-cut pear pulp tissue was added to 8mL of 1% HCl-methanol solution in an ice bath, ground, and then diluted to a 25mL brown volumetric flask. Extraction was performed at 4°C in the dark for 20min, shaken and filtered, and the absorbance of the filtrate was measured at a wavelength of 280nm. The absorbance was adjusted to zero with 1% HCl-methanol solution, and the data were recorded. The measurement was repeated three times. The total phenol content was expressed as the absorbance value per gram of fresh-cut pear pulp tissue at a wavelength of 280nm, which is OD 280 / g.

[0115] (3) Determination of glutathione content

[0116] Glutathione was determined using the method provided by Nanjing Jiancheng Glutathione Kit, and the content was expressed in mg / kg.

[0117] The test results are as follows Figure 8 As shown:

[0118] Phenolic substances, ascorbic acid (AsA), and glutathione (GSH) are the main antioxidants in crown pear fruit that have the function of scavenging ROS. Figure 8 As shown in the figure, the three antioxidant substances showed a downward trend after the storage of fresh-cut pears.

[0119] Depend on Figure 8 aIt can be seen that the polyphenol content of fresh-cut pears in the different quantum dot coating liquid treatment groups showed a trend of first increasing and then decreasing, and the treated groups were always higher than the control group during storage. The reason for this may be that the fresh-cut pears were mechanically damaged during processing, resulting in secondary metabolic reactions, and phenolic substances are the most widely present secondary metabolites in plants; on the other hand, oxidized phenolic substances can be reduced back to phenolic substances under the reducing effect of ascorbic acid. Therefore, at the beginning of storage, the total phenol content of the different treatment groups still showed an upward trend and maintained a relatively high level. The experimental results show that the addition of the three quantum dots can effectively enhance the retention of phenolic substances in fresh-cut pears by chitosan coating during storage. In comparison, the chitosan coating with the addition of E / NPER-CDs can more effectively slow down the consumption of phenolic substances in fresh-cut pears during storage. After 5 days of storage, the total phenol content of the CS / E / NPER-CDs coating treatment group was 0.28OD 280 / g, which is 1.4 times that of the control group.

[0120] Ascorbic acid is an important nutrient in fresh-cut pears, and the change in its content during storage of fresh-cut fruits and vegetables is an important indicator for measuring the preservation effect. Figure 8 As shown in Figure b, the ascorbic acid content of fresh-cut pears decreased continuously during storage, likely due to ascorbic acid's participation in the reduction of quinones. The control group experienced the greatest and fastest decline. By day 5 of storage, the ascorbic acid content in the control group had decreased by 68.1%, while the ascorbic acid content in the CS / E / NPER-CDs coating group had only decreased by 39.5% after the end of storage. These results demonstrate that the CS / E / NPER-CDs coating effectively reduces ascorbic acid loss in fresh-cut pears.

[0121] Depend on Figure 8 As shown in Figure 3, GSH content in fresh-cut pears showed a downward trend across all treatment groups. GSH content in the CS / PER-CDs, CS / EPER-CDs, and CS / E / NPER-CDs coating groups was significantly (P < 0.05) higher than in the control group. After five days of storage, GSH content in the control group was only 78.64%, 72.78%, and 70.67% of that in the CS / PER-CDs, CS / EPER-CDs, and CS / E / NPER-CDs coating groups, respectively. CS / E / NPER-CDs coating was the most effective in reducing GSH loss in fresh-cut pears.

[0122] 3. ROS content determination

[0123] (1) Determination of H2O2 content

[0124] The H2O2 content in fresh-cut pear tissue was determined using the method provided by the Nanjing Jiancheng Hydrogen Peroxide Assay Kit. The final H2O2 content was expressed in nmol g -1 FW said.

[0125] (2)O2 ·- Content determination

[0126] O2 ·- The determination of O2 was carried out according to the existing literature [Fungal Biology, 2018, 122(5): 310-321] with slight modifications. 0.15g of fresh-cut pear pulp tissue was taken to determine the final O2 ·- The content is expressed as nmol g -1 FW min -1 .

[0127] The test results are as follows Figure 9 As shown:

[0128] H2O2、O2 ·-Excessive accumulation of can cause peroxidation of cell membrane lipids in fresh-cut pears, accelerating the aging and browning of fresh-cut pears. - The impact of Figure 9 As shown, H2O2 content and O2 ·- The contents of H2O2 and O2 in fresh-cut pears treated with CS / EPER-CDs and CS / E / NPER-CDs coatings showed a trend of increasing first and then decreasing. ·- The results were significantly lower than those in the control group, which may be due to the fact that EPER-CDs and E / NPER-CDs played a role in clearing H2O2 and O2 ·- During the entire storage period, the CS / EPER-CDs and CS / E / NPER-CDs coatings delayed the H2O2 and O2 ·- The peak of H2O2 and O2 ·- The peak value of free radical content was observed in the treatment with CS / E / NPER-CDs film. The above results showed that CS / E / NPER-CDs film could effectively inhibit the accumulation of free radicals in fresh-cut pears during storage.

[0129] 4. Determination of ROS metabolism-related enzyme activities

[0130] (1) SOD activity determination

[0131] The SOD activity in fresh-cut pear pulp tissue was determined using the method for determining SOD in plant tissue provided in the Nanjing Jiancheng kit, and the results were expressed as U mg -1 , where U is the amount of enzyme corresponding to 50% SOD inhibition rate in the reaction system, that is, one SOD activity unit.

[0132] (2) CAT activity assay

[0133] Catalase activity in fresh-cut pear pulp tissue was determined using the method for determining CAT in plant tissues provided in the Solebro kit, and the results were expressed as U mg -1 .

[0134] (3) POD activity assay

[0135] Peroxidase activity in fresh-cut pear pulp tissue was determined using the method for determining POD in plant tissue provided by Nanjing Jiancheng kit, and the results were expressed as U mg -1 .

[0136] (4) PPO activity determination

[0137] Determination of polyphenol oxidase The activity of PPO in fresh-cut pear pulp tissue was determined using the method for determining PPO in plant tissue provided by Nanjing Jiancheng kit, and the results were expressed as U mg -1 .

[0138] (5) APX activity assay

[0139] Ascorbate peroxidase activity in fresh-cut pear pulp tissue was determined using the method for determining APX in plant tissue provided in the Nanjing Jiancheng kit. The results were expressed as U mg -1 .

[0140] The test results are as follows Figure 10 As shown:

[0141] Superoxide dismutase (SOD) and catalase (CAT) are important antioxidant enzymes in the crown pear. Within the pear's direct antioxidant system, the clearance of reactive oxygen species (ROS) is primarily related to antioxidant enzyme activity. SOD catalyzes the conversion of O2·- to H2O2, while CAT decomposes the resulting H2O2 into H2O and CO2. Peroxidase (POD) is a type of oxidase present in pears that acts synergistically with SOD and CAT. It can also serve as a physiological indicator of tissue aging. APX (ascorbic acid oxidase) catalyzes the conversion of ascorbic acid and H2O2 to H2O. Polyphenol oxidase (PPO) is a metalloproteinase in pear flesh that oxidizes phenolic compounds into quinones.

[0142] Depend on Figure 10 a and Figure 10 b It can be seen that during the storage period, the activities of SOD and CAT in the pulp tissue of fresh-cut pears treated with different quantum dot coatings showed a trend of first increasing and then decreasing. Compared with the control group, the CS / PER-CDs, CS / EPER-CDs and CS / E / NPER-CDs coating treatments reduced the activities of SOD and CAT to varying degrees, among which the CS / E / NPER-CDs coating treatment delayed the arrival of the peak activities of SOD and CAT enzymes. Until the fourth day of storage, the SOD activity of the CS / E / NPER-CDs coating treatment group reached 87.82U / mg, which was only 86.5% of the peak value of the control group. This result is consistent with the previous different treatments on the O2 ·- The results of the content echo each other, O2 ·- The content increased rapidly, resulting in a rapid increase in SOD activity. On the second day of storage, the O2 ·- The content and SOD enzyme activity reached the peak value. In contrast, in the CS / E / NPER-CDs coating treatment group, the O2 ·-The accumulation process of O2 ·- The content reached a peak, and the SOD activity reached a peak on the 4th day.

[0143] Depend on Figure 10 c. Figure 10 d and Figure 10 It can be seen that during the storage period, the POD and APX activities of the different treatment groups first increased and then decreased, while the PPO activity showed an upward trend. However, the POD, APX and PPO activities of the groups treated with CS / PER-CDs, CS / EPER-CDs and CS / E / NPER-CDs coatings were significantly lower than those of the control group, among which the CS / E / NPER-CDs coating group had the lowest POD, APX and PPO activities. This may be because E / NPER-CDs has good oxidative activity, which plays a role in scavenging some free radicals, and chitosan can form a thin film on the surface of fresh-cut pears that can block oxygen, effectively protecting the membrane structure of fresh-cut pears and inhibiting O2 ·- and H2O2 accumulation, thereby reducing the activity of POD, APX and PPO. In the later storage period, POD and APX can maintain a high activity and thus have a strong scavenging effect on free radicals, which is conducive to maintaining good storage quality of fresh-cut pears.

[0144] It can be seen that CS / E / NPER-CDs coating can significantly reduce the activities of SOD, CAT, POD, APX and PPO in fresh-cut pears and delay the arrival of the peak activities of SOD, CAT, POD and APX. This also proves that CS / E / NPER-CDs coating can effectively delay O2 ·- The accumulation level of H2O2 reduces the oxidative damage of the fruit caused by active oxygen, achieving the effect of preserving freshness.

[0145] In summary, CS / E / NPER-CDs coating treatment can significantly inhibit ROS (O2 ·- and H2O2), delaying the degradation of total phenols, ascorbic acid (AsA), and glutathione (GSH), while significantly reducing the activities of SOD, CAT, POD, APX, and PPO, and delaying the peaks of SOD, CAT, POD, and APX, so as to achieve the effect of improving the quality of fresh-cut pears during storage, and has broad application prospects.

[0146] The present invention also provides other feasible embodiments, as shown below:

[0147] Example 3

[0148] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0149] 1.5 g of Pleurotus eryngii root powder, 0.7 g of EDTA-Na₂, and 0.6 g of citric acid were mixed with 70 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0150] Example 4

[0151] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0152] 1.0 g of Pleurotus eryngii root powder, 0.4 g of EDTA-Na₂, and 0.4 g of citric acid were mixed with 60 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0153] Example 5

[0154] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0155] 2.0 g of Pleurotus eryngii root powder, 0.8 g of EDTA-Na₂, and 0.8 g of citric acid were mixed with 100 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0156] Example 6

[0157] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0158] 1.0 g of Pleurotus eryngii root powder, 0.2 g of EDTA-Na₂, and 0.2 g of citric acid were mixed with 50 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0159] Example 7

[0160] Preparation of quantum dots E / NPER-CDs, the steps are as follows:

[0161] 2.5 g of Pleurotus eryngii root powder, 1.0 g of EDTA-Na₂, and 1.0 g of citric acid were mixed with 110 mL of ultrapure water. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor. The mixture was then placed in a high-temperature drying oven at 180°C for 8 h. The resulting product was centrifuged at 10,000 g, and the supernatant was collected and filtered through a 0.22 μm filter. The filtrate was purified by dialysis with a molecular weight cutoff of 500 Da for 48 h. The dialyzate was lyophilized to obtain E / NPER-CDs powder. The powder was stored in a desiccator to prevent moisture absorption.

[0162] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for preparing quantum dot E / NPER-CDs, characterized in that: The steps include: Pleurotus eryngii root powder, EDTA-Na2 and citric acid were added to water and reacted at high temperature. After the reaction was completed, the mixture was centrifuged and the supernatant was dialyzed. The dialyzate was then freeze-dried to obtain quantum dots E / NPER-CDs. The mass ratio of the Pleurotus eryngii root powder, EDTA-Na2 and citric acid is selected from 4~6: 1~3: 1~3; the mass volume ratio of the Pleurotus eryngii root powder to water is selected from 1:40~64, g / mL; the conditions of the high temperature reaction are selected from: treatment at 140~200°C for 2~10h.

2. Quantum dot E / NPER-CDs prepared by the method of claim 1.

3. Use of the quantum dot E / NPER-CDs according to claim 2 in food antioxidant and / or antibacterial properties.

4. A chitosan / quantum dot coating solution, characterized in that: The method is as follows: the quantum dot E / NPER-CDs solution according to claim 2 is mixed with a chitosan solution, and the mixture is stirred to obtain a chitosan / quantum dot coating solution.

5. The chitosan / quantum dot coating solution according to claim 4, characterized in that The concentration of the chitosan solution is selected from 0.8 to 1.2%.

6. The chitosan / quantum dot coating solution according to claim 4, characterized in that The concentration of the quantum dot E / NPER-CDs solution is selected from 80 to 120 mg / mL.

7. Use of the quantum dot E / NPER-CDs according to claim 2 or the chitosan / quantum dot coating solution according to any one of claims 4 to 6 in food preservation.

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