Banana peel carbon quantum dot visual antibacterial preservative film and preparation method thereof

Abstract

The invention belongs to the technical field of preservative films, and discloses a banana peel carbon quantum dot visual antibacterial preservative film and a preparation method thereof.The method comprises the steps that S1, banana peel carbon quantum dot powder is prepared; s2, preparing an anthocyanin and curcumin mixed pigment; s3, preparing a gelatin solution; s4, preparing a chitosan solution; s5, mixing the gelatin solution and the chitosan solution, and adding the banana peel carbon quantum dot powder, a mixed pigment, a plasticizer and a cross-linking agent to obtain a film-forming solution; s6, adding dye, adjusting the pH value of the solution to 5.0-5.5, and removing bubbles; and S7, coating on a substrate, drying, stripping to obtain a film body, and adjusting the film body in a cabinet containing a Mg (NO3) 2 saturated solution at 25 DEG C and 50% RH for at least 48 hours to obtain the preservative film. The banana peel carbon quantum dots conform to the characteristics of a nano bacteriostatic agent, and the prepared preservative film has excellent bacteriostatic performance and better preservation effect; in the food deterioration process, the pH changes, the color of the preservative film changes accordingly, and reference can be provided for judging the deterioration condition of food packaged by the preservative film.

Description

Technical Field

[0001] The invention belongs to the technical field of cling film, and in particular relates to a banana peel carbon quantum dot visualized antibacterial cling film and a preparation method thereof. Background Art

[0002] Carbon quantum dots (CQDs), also known as carbon dots or carbon nanodots, are a class of zero-dimensional carbon nanomaterials with significant fluorescence properties. They are composed of ultrafine, dispersed, quasi-spherical carbon nanoparticles with a size of less than 10 nm.

[0003] Cling film is widely used in food preservation in refrigerators, packaging of fresh and cooked food, and in food packaging in families, supermarkets, hotels, restaurants, and industrial production. Antibacterial cling film generally adds antibacterial agents or antibacterial genes to the matrix material forming the film to inhibit or kill microorganisms such as bacteria and fungi, thereby producing an antibacterial or antibacterial effect on the packaging object to extend the shelf life of the food.

[0004] The invention provides a study on the preparation of banana peel carbon quantum dot antibacterial cling film, and obtains an antibacterial cling film with high antibacterial activity, inhibits the growth and reproduction of bacteria, and provides another idea for the antibacterial cling film. In addition, the color change property of the pigment as the pH value of the food changes when the food is spoiled is utilized to make a visual antibacterial cling film, and provides a reference for judging the spoilage of the food. Summary of the invention

[0005] The invention provides a banana peel carbon quantum dot visualized antibacterial cling film and a preparation method thereof. Banana peel is used as a raw material to prepare carbon quantum dots, which are then mixed with a gelatin solution, a chitosan solution, anthocyanin curcumin mixed pigments and the like to obtain a film-forming solution, which is finally thinly coated and dried to form a film, thereby obtaining a visualized antibacterial cling film with an antibacterial effect and capable of changing color with pH.

[0006] The present invention adopts the following technical solutions:

[0007] The preparation method of banana peel carbon quantum dot visual antibacterial cling film comprises the following steps:

[0008] S1. The dried banana peel is crushed and sieved to obtain banana peel powder, the banana peel powder is fully mixed with deionized water and then loaded into a polytetrafluoroethylene-lined hydrothermal reactor for oil bath heating, the supernatant is centrifuged after cooling, the supernatant is filtered and transferred into a dialysis bag for dialysis, and the liquid in the bag is freeze-dried after dialysis to obtain banana peel carbon quantum dot powder, which is sealed and stored below 4°C;

[0009] S2. preparing anthocyanin and curcumin mixed pigment solution;

[0010] S3. The gelatin and deionized water were mixed in a mass ratio of 1:23-27 to prepare a gelatin solution;

[0011] S4. chitosan and 2% acetic acid solution were mixed in a mass ratio of 1:45-55 to prepare a chitosan solution;

[0012] S5. The gelatin solution and the chitosan solution were mixed in a ratio of 1:1, banana peel carbon quantum dot powder was added, a mixed pigment solution, a plasticizer, and a cross-linking agent were added, and the mixture was stirred at 45°C to obtain a film-forming solution;

[0013] S6. Add dye to the film-forming solution, adjust the pH value of the solution to 5.0-5.5, and vacuum degas to remove bubbles;

[0014] S7. Apply the defoamed solution to the substrate, peel it off after drying to obtain a film body, and adjust the mold body in a cabinet containing a saturated solution of Mg(NO3)2 at 25°C and 50% RH for at least 48 hours to obtain a cling film.

[0015] Preferably, in S5, the mass ratio of banana peel carbon quantum dot powder to chitosan is 1:13-40.

[0016] Preferably, the chitosan in S4 has a deacetylation degree of 85% and a diameter of 141,000 Da.

[0017] Preferably, the ratio of gelatin to deionized water in S3 is 1:25, and the ratio of chitosan to acetic acid solution in S3 is 1:50.

[0018] Preferably, the preparation process of anthocyanin and curcumin mixed pigment is as follows:

[0019] The grape skin was dried at room temperature and ground into powder, and the grape skin powder was added into acidified ethanol (ethanol: 1 mol / L hydrochloric acid = 85:15), the mass ratio of grape skin powder to acidified ethanol was 1:20, the solution was stored at 4°C in the dark for 24 hours, and then ultrasonically extracted at 50°C with a power of 270W for 30 minutes, after ultrasonic treatment, the mixture was filtered to collect the supernatant, and then rotary evaporated at 45°C to remove ethanol, and then the solution was freeze-dried to obtain a powder, which was stored in a brown reagent bottle at 4°C for use;

[0020] Dissolve curcumin powder in 75% ethanol solution to prepare curcumin solution, the mass ratio of curcumin powder to ethanol solution is 1:40, and store at 4°C in the dark;

[0021] The grape skin extract and the curcumin solution were mixed in a mass ratio of 1:20 to obtain a mixed pigment solution, which was stored at 4° C. in the dark.

[0022] Preferably, in S5, the volume ratio of the added mixed pigment solution to the chitosan solution is 2-3:100.

[0023] Preferably, in S5, the cross-linking agent is a 0.25% sodium tripolyphosphate solution, and the added amount accounts for 1%-3% of the volume of the mixed solution.

[0024] Preferably, the pH is adjusted to 5.3 in S6.

[0025] The present invention also provides a banana peel carbon quantum dot visualized antibacterial fresh-keeping film prepared by the method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The banana peel carbon quantum dots prepared by the preparation method meet the characteristics of nano antibacterial agents, and the product banana peel carbon quantum dots visualized antibacterial cling film has excellent antibacterial properties, thus being able to play a longer-term and better preservation role compared to ordinary cling film;

[0028] Under different pH environments, the change in the molecular structure of the two pigments will cause the plastic wrap to undergo visible color changes. When the pH value is less than 3.0, it is orange-red; when the pH value is between 3.0-6.0, it changes from orange-red to yellow; when the pH value is greater than 6.0, it changes to green; as the pH of food deteriorates, the color of the plastic wrap also changes accordingly. This can provide a reference for judging the deterioration of food wrapped in plastic wrap. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below. Unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are conventional methods in the art. The embodiments described below are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0030] Embodiment 1

[0031] Hydrothermal synthesis of carbon quantum dots:

[0032] The dried banana peels are crushed with a crusher and sieved to obtain banana peel powder;

[0033] Take banana peel powder, add deionized water, mix thoroughly, load it into a polytetrafluoroethylene-lined hydrothermal reactor, and then heat the reactor in a 100°C oil bath for 4 hours. After cooling, take out the reaction product and centrifuge it at 9000rpm for 30 minutes, and keep the supernatant.

[0034] The supernatant was filtered through a filter and transferred to a dialysis bag for dialysis. After dialysis, the liquid in the bag was lyophilized and the resulting powder was sealed in a plastic bag and stored at 4°C.

[0035] Preparation of anthocyanin and curcumin mixed pigment:

[0036] The grape skins were dried at room temperature and ground into powder;

[0037] 2.5 g of grape skin powder was added to 50 mL of acidified ethanol (ethanol: 1 mol / L hydrochloric acid = 85:15), the solution was stored at 4°C in the dark for 24 hours, and then ultrasonically extracted at 50°C with a power of 270 W for 30 min. After ultrasonic treatment, the mixture was filtered to collect the supernatant, and then rotary evaporated at 45°C to remove the ethanol; the solution was freeze-dried, and the obtained powder was stored in a brown reagent bottle at 4°C for use;

[0038] Dissolve 0.5 g of curcumin powder in 20 ml of 75% ethanol solution to prepare curcumin solution, and store at 4 °C in the dark;

[0039] 0.5 g of grape skin extract and 10 ml of curcumin solution were mixed to obtain a mixed pigment, which was stored at 4° C. in the dark.

[0040] Prepare gelatin solution:

[0041] A single gelatin solution was prepared by dissolving 4 g of gelatin (G) in 100 g of deionized water and then continuously stirring at 45°C for 30 min.

[0042] Prepare chitosan solution:

[0043] 2 g of chitosan with a deacetylation degree of 85% and a molecular weight of 141,000 Da (Ch) was dissolved in 100 g of a 2% acetic acid solution (v / w), stirred at 450 rpm for 12 hours, and then filtered through a micron wire mesh to remove impurities, thereby preparing a chitosan solution.

[0044] The gelatin solution and the chitosan solution were mixed, 0.05 g of banana peel carbon quantum dot powder (3 wt% based on G+Gh) and 2-3 ml of mixed pigment were added, 1.8 g of glycerol was added as a plasticizer, 4 ml of 0.25% sodium tripolyphosphate solution was added as a cross-linking agent, and the mixture was heated and stirred at 45° C. for 30 minutes to obtain a film-forming solution;

[0045] Then, 4% (v / v) of the dye was added to the film-forming solution, and the pH value of the solution was adjusted to 5.3 and stirred with a magnetic stirrer for 2 hours. The film-forming solution was then degassed under vacuum for 15 minutes to remove bubbles.

[0046] Then, an aliquot of the defoamed film-forming solution was poured into a polystyrene petri dish and dried at 23-25°C for 48 hours. The dried film was peeled off the plate and then conditioned in a cabinet containing a saturated solution of Mg(NO3)2 at 25°C and 50% RH for 48 hours.

[0047] The obtained banana peel carbon quantum dot visualized antibacterial cling film has good antibacterial properties. In addition, under different pH environments, the color of the cling film changes due to the changes in the molecular structures of the two pigments themselves: when the pH value is less than 3.0, the cling film is orange-red; when the pH value is between 3.0 and 6.0, the cling film is yellow; when the pH value is greater than 6.0, the cling film is green. The reason is that anthocyanidins mainly exist in the form of red yellow salt anthocyanins under acidic conditions, while curcumin is yellow, and the mixture shows orange-red; as the acidity gradually weakens, anthocyanidins are transformed into pseudoalkalis or chalcone, the red color fades, and the yellow color of curcumin gradually appears; when the pH value rises to neutral, anthocyanidins are transformed into blue quinone glycosides, which work together with brown-yellow curcumin to show green.

[0048] Antimicrobial performance tests are divided into antibacterial tests and antifungal tests.

[0049] Antibacterial test:

[0050] Main tools:

[0051] Constant temperature incubator (37±1)℃, refrigerator 0℃~5℃, clean workbench, biological optical microscope, pressure steam sterilizer electric drying oven, sterilized plates, sterilized test tubes, sterilized pipettes, inoculation loops, alcohol lamp, and polyethylene film covering film.

[0052] Control sample: ordinary cling film, 50mm*50mm, thickness about 0.01mm.

[0053] Test sample: antibacterial cling film, 50mm*50mm, thickness about 0.01mm.

[0054] Before the test, the sample surface was wiped with 70% ethanol solution, rinsed with sterile water after 1 min, and dried naturally.

[0055] Nutritious broth

[0056] Take 5.0g of beef extract, 10.0g of peptone and 5.0g of sodium chloride and add them to 1000mL of distilled water. Heat to dissolve, adjust the pH to 7.0-7.2 after sterilization with 0.1mol / L sodium hydroxide solution, divide the mixture into portions and place them in a pressure steam sterilizer, and sterilize at 121℃ for 30min.

[0057] Nutrient agar medium

[0058] Add 15 g of agar to 1000 mL of nutrient broth, heat to dissolve, adjust the pH to 7.0-7.2 with 0.1 mol / L sodium hydroxide solution after sterilization, divide into portions and place in a pressure steam sterilizer, sterilize at 121°C for 30 min.

[0059] Disinfectants

[0060] 70% ethanol solution

[0061] Eluent

[0062] Physiological saline containing 0.80% sodium chloride. A small amount of sterile surfactant can be added to facilitate elution. Use 0.1 mol / L sodium hydroxide solution or 0.1 mol / L hydrochloric acid solution to adjust the pH to 7.0-7.2 after sterilization. Place the aliquots in a pressure steam sterilizer and sterilize at 121℃ for 30 minutes.

[0063] Test strains

[0064] Staphylococcus aureus

[0065] Escherichia coli

[0066] Culture medium

[0067] Nutrient broth / physiological saline solution. The concentration for Escherichia coli is 1 / 500, and the concentration for Staphylococcus aureus is 1 / 100. A small amount of non-toxic surfactant can be added to facilitate bacterial dispersion. Use 0.1 mol / L sodium hydroxide solution or 0.1 mol / L hydrochloric acid solution to adjust the pH to 7.0-7.2 after sterilization, and place in a pressure steam sterilizer after packaging, and sterilize at 121℃ for 30 minutes.

[0068] Procedure

[0069] Strain preservation

[0070] The strain was inoculated on a slant of nutrient agar medium, cultured at (37+1)°C for 24 hours, and then stored at 0-5°C as slant-preserved bacteria.

[0071] Bacteria activation

[0072] Transfer the slant-preserved bacteria to a nutrient agar plate and culture at (37±1)℃ for 24h, transferring once a day. The bacterial culture after two consecutive transfers should be used in the test.

[0073] Preparation of bacterial suspension

[0074] Use an inoculation loop to take a small amount (scrape 1-2 loops) of fresh bacteria from the culture medium, add it to the culture medium, and make 10-fold incremental dilutions in sequence, selecting a bacterial solution concentration of 5.0x10 5 cfu / mL~10.0x10 5 The dilution with the concentration of cfu / mL was used as the test bacterial solution and the test was carried out according to the method of GB / T 4789.2.

[0075] Sample test

[0076] Take 0.2 mL of the test bacterial solution and drop it on the blank control sample and the antibacterial cling film sample respectively, and make 5 parallels for each sample.

[0077] Cover the samples with sterile covering films, spread them flat so that the bacteria are evenly in contact with the samples, place them in sterile plates, and culture them at (37±1)℃ and relative humidity greater than 90% for 24 hours. Take out the samples that have been cultured for 24 hours, add 20mL of eluent respectively, wash the samples and covering films repeatedly, shake well, take a certain amount and inoculate it in nutrient agar medium, culture them at (37±1)℃ for 24 to 48 hours, and count the live bacteria. Determine the number of live bacteria according to the method of GB / T4789.2.

[0078] Test result calculation

[0079] The measured viable bacterial count result was multiplied by 100 to obtain the actual number of viable bacteria recovered after 24 hours of sample culture.

[0080] The antibacterial rate is calculated according to the formula:

[0081] R(%)=(BC) / Bx100

[0082] In the formula: R--antibacterial rate, %; B--average number of recovered bacteria in blank control samples, cfu / piece; C--average number of recovered bacteria in antibacterial cling film samples, cfu / piece.

[0083] The test results showed that the antibacterial rate was 99.2%.

[0084] Anti-mold test, by directly observing the degree of mold growth to evaluate the mold growth level of antibacterial plastics

[0085] Main Equipment

[0086] Constant temperature and humidity incubator (28±1)℃ and relative humidity greater than 90%, refrigerator 0℃~10℃, clean bench, centrifuge, biological optical microscope, pressure steam sterilizer, electric drying oven, blood cell counting plate, sterile plates, sterile test tubes, sterile pipettes, sterile centrifuge tubes, sterile conical flasks, inoculation loops, alcohol lamp.

[0087] Control sample: ordinary cling film, 50mm*50mm, thickness about 0.01mm.

[0088] Antibacterial plastic sample: antibacterial cling film, 50mm*50mm, thickness about 0.01mm.

[0089] All samples should be disinfected before testing. Wipe the sample surface with disinfectant (70% ethanol solution), rinse with sterile water after 1 minute, and dry naturally.

[0090] Reagents and media

[0091] Nutrient salt culture medium

[0092] Take 2.0g of sodium nitrate, 2.0g of potassium dihydrogen phosphate, 0.3g of dipotassium hydrogen phosphate, 0.5g of potassium chloride, 0.5g of magnesium sulfate, 0.01g of ferrous sulfate, and 30g of sucrose, add to 1000mL of 0.05% wetting agent aqueous solution, heat to dissolve, adjust the pH with 0.1mol / L sodium hydroxide solution to pH 6.0-6.5 after sterilization, and sterilize in a pressure steam sterilizer at 115℃ for 30min.

[0093] Nutrient salt agar medium

[0094] Add 15g of agar to 1000mL of nutrient salt culture medium, heat to dissolve, adjust the pH with 0.1mol / L sodium hydroxide solution to pH6.0-6.5 after sterilization, and sterilize in a pressure steam sterilizer at 115℃ for 30min after packaging. Potato-glucose agar medium (PDA) Wash the potatoes with water, peel and cut into small pieces. Weigh 200g, add 1000mL of distilled water, and heat to boil for 1h. Then squeeze out the filtrate with double gauze, add 1000mL of distilled water to the filtrate, add 20g of glucose and 20g of agar, heat to dissolve, adjust the pH with 0.1mol / L sodium hydroxide solution to pH6.0-6.5 after sterilization, and sterilize at 115℃ for 30min.

[0095] Disinfectants

[0096] 70% ethanol solution.

[0097] Eluent

[0098] A 0.05% aqueous solution of TUV DIMETHICONE was prepared. The pH was adjusted to 6.0-6.5 after sterilization and sterilized at 115℃ for 30 minutes.

[0099] Bacteria

[0100] Aspergillus niger, Aspergillus terreus, Paecilomyces variotii, Penicillium cordiformis, Budding short stalk, Chaetomium globosum

[0101] Procedure

[0102] Strain preservation

[0103] The strains were inoculated on potato-glucose agar medium slants, cultured at 28°C to 30°C for 7 days, and then stored at 5°C to 10°C as preserved bacteria.

[0104] Bacteria activation

[0105] Inoculate the preserved bacteria in a PDA slant medium test tube and culture for 7 days to generate a large number of spores. Do not remove the cotton plug before preparing the spore suspension. Each opening of a tube is only for preparing one suspension, and each time the spore suspension is prepared, freshly cultured mold spores must be used.

[0106] Spore suspension preparation

[0107] Add a small amount of sterile distilled water to the PDA slant culture medium within 7 days of culture, gently scrape the fresh mold spores on the surface with a sterilized inoculation needle, place the spore suspension in a 250mL conical flask, and then inject 40mL of eluent.

[0108] Add 15 glass beads with a diameter of 5 mm to the conical flask and mix with the spores. After sealing, place it in a water bath oscillator and oscillate continuously to disperse the clumped spores. Then filter it with a single layer of gauze to remove the hyphae. Put it into a sterile centrifuge tube, separate the precipitated spores with a centrifuge, and remove the supernatant. Then add 40 mL of the eluent and repeat the centrifugation operation 3 times.

[0109] Dilute the spore suspension with nutrient solution and count with a hemocytometer to make a concentration of (1X10 5 ±2x10 5 )spores / mL of fungal spore suspension.

[0110] The spore suspensions of the six fungi were prepared using the above method. The spore suspensions were mixed together and fully shaken to make them evenly dispersed.

[0111] The mixed spore suspension should be used on the same day.

[0112] Plate culture medium preparation

[0113] Inject nutrient salt agar medium into a sterile plate with a thickness of 3-6 mm and set aside after solidification (use within 48 hours).

[0114] Sample test

[0115] The blank control sample and the antibacterial cling film sample were spread on the flat culture medium respectively, and the spore suspension was sprayed so that it was fully and evenly sprayed on the culture medium and the sample. Five parallels were made for each sample.

[0116] The above samples were cultured for 28 days at a temperature of 28°C and a relative humidity greater than 90%.

[0117] The above experiment was repeated twice.

[0118] The samples must be observed immediately after they are taken out. The moldy area of ​​the blank control sample should not be less than 10%, otherwise it cannot be used as the blank control sample for the test.

[0119] Sample mold growth level:

[0120] Level 0: No growth, i.e. no growth observed under a microscope (magnification 50 times):

[0121] Level 1: trace growth, i.e. growth is visible to the naked eye, but the growth covers less than 10% of the area;

[0122] Level 2: Growth coverage is not less than 10%.

[0123] The test results showed that the mold growth level of the antibacterial plastic wrap was level 0.

[0124] Visual color change test

[0125] Acidic and alkaline solutions with gradient pH values ​​were prepared and applied to test the color change of the plastic wrap. The color change in the test was in line with expectations.

[0126] Test Supplies

[0127] Fresh apples, visual antibacterial cling film (thickness 0.01mm)

[0128] Test steps

[0129] Rinse the skin of two fresh, whole apples of similar size and cut each into four pieces. Wrap each piece tightly with plastic wrap, for a total of 8 groups. Place the wrapped apples at 28°C.

[0130] The plastic wrap was originally yellow. One hour after wrapping the apple, the yellow color of the part that was in contact with the cut surface of the apple slightly deepened, and then the color did not change significantly for a short period of time. Thereafter, the color of the plastic wrap in that part was observed every 24 hours.

[0131] Test results

[0132] There was no significant change in the color of the plastic wrap during the first three days; from the fourth to the seventh day, the yellow color of the plastic wrap became darker and gradually darker, until it turned into orange-red on the seventh day. Moldy growth could be observed on the cut surface of the apple on the sixth day.

[0133] This indicates that the visual antibacterial cling film obtained by the present invention can reflect the deterioration of food to a certain extent, and can provide a reference for judging the deterioration of food.

[0134] Embodiment 2

[0135] The preparation and test process were the same as those in Example 1, except that: during the preparation process, after the gelatin solution and the chitosan solution were mixed, 0.10 g of banana peel carbon quantum dot powder was added.

[0136] Antibacterial test results

[0137] The antibacterial rate is 99.9% and the mold growth level is 0.

[0138] Visualize color change test results

[0139] The color change of the plastic wrap was tested by brushing with acid and alkaline solutions with stepwise pH values. The color change in the test was as expected; the color of the plastic wrap darkened as the apples deteriorated.

[0140] Embodiment 3

[0141] The preparation and test process were the same as in Example 1, except that: during the preparation process, after the gelatin solution and the chitosan solution were mixed, 0.15 g of banana peel carbon quantum dot powder was added.

[0142] Antibacterial test results

[0143] The antibacterial rate is 99.8% and the mold growth level is 0.

[0144] Visualize color change test results

[0145] The color change of the plastic wrap was tested by brushing with acid and alkaline solutions with stepwise pH values. The color change in the test was as expected; the color of the plastic wrap darkened as the apples deteriorated.

[0146] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the above embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a banana peel carbon quantum dot visual antibacterial cling film, characterized in that: The following steps are involved: S1. The dried banana peel is crushed and sieved to obtain banana peel powder, the banana peel powder is fully mixed with deionized water and then loaded into a polytetrafluoroethylene-lined hydrothermal reactor for oil bath heating, the supernatant is centrifuged after cooling, the supernatant is filtered and transferred into a dialysis bag for dialysis, and the liquid in the bag is freeze-dried after dialysis to obtain banana peel carbon quantum dot powder, which is sealed and stored below 4°C; S2. preparing anthocyanin and curcumin mixed pigment solution; S3. The gelatin and deionized water were mixed in a mass ratio of 1:23-27 to prepare a gelatin solution; S4. chitosan and 2% acetic acid solution were mixed in a mass ratio of 1:45-55 to prepare a chitosan solution; S5. The gelatin solution and the chitosan solution were mixed in a ratio of 1:1, banana peel carbon quantum dot powder was added, a mixed pigment solution, a plasticizer, and a cross-linking agent were added, and the mixture was stirred at 45°C to obtain a film-forming solution; S6. Add dye to the film-forming solution, adjust the pH value of the solution to 5.0-5.5, and vacuum degas to remove bubbles; S7. Apply the defoamed solution to the substrate, peel it off after drying to obtain a film body, and adjust the mold body in a cabinet containing a saturated solution of Mg(NO3)2 at 25°C and 50% RH for at least 48 hours to obtain a cling film.

2. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 1, characterized in that: In S5, the mass ratio of banana peel carbon quantum dot powder to chitosan is 1:13-40.

3. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 1, characterized in that: The chitosan in S4 has a deacetylation degree of 85% and a size of 141,000 Da.

4. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 3, characterized in that: The ratio of gelatin to deionized water in S3 was 1:25, and the ratio of chitosan to acetic acid solution in S3 was 1:

50.

5. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 1, characterized in that: Preparation process of anthocyanin and curcumin mixed pigment: The grape skin was dried at room temperature and ground into powder, and the grape skin powder was added into acidified ethanol (ethanol: 1 mol / L hydrochloric acid = 85:15), the mass ratio of grape skin powder to acidified ethanol was 1:20, the solution was stored at 4°C in the dark for 24 hours, and then ultrasonically extracted at 50°C with a power of 270W for 30 minutes, after ultrasonic treatment, the mixture was filtered to collect the supernatant, and then rotary evaporated at 45°C to remove ethanol, and then the solution was freeze-dried to obtain a powder, which was stored in a brown reagent bottle at 4°C for use; Dissolve curcumin powder in 75% ethanol solution to prepare curcumin solution, the mass ratio of curcumin powder to ethanol solution is 1:35-45, and store at 4°C in the dark; The grape skin extract and the curcumin solution were mixed in a mass ratio of 1:15-25 to obtain a mixed pigment solution, which was stored at 4° C. in the dark.

6. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 5, characterized in that: In S5, the volume ratio of the added mixed pigment solution to the chitosan solution is 2-3:

100.

7. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 1, characterized in that: In S5, the cross-linking agent is a 0.25% sodium tripolyphosphate solution, and the amount of the cross-linking agent added accounts for 1%-3% of the volume of the mixed solution.

8. The method for preparing the banana peel carbon quantum dot visual antibacterial cling film according to claim 1, characterized in that: The pH was adjusted to 5.3 in S6.

9. A banana peel carbon quantum dot visualized antibacterial cling film prepared by the method for preparing a banana peel carbon quantum dot visualized antibacterial cling film according to any one of claims 1 to 8.