Preparation method of multifunctional novel carbon dot gelatin shell chitosan-based intelligent packaging film

Abstract

The application discloses a preparation method of a multifunctional novel carbon dot gelatin / chitosan-based intelligent packaging film, relates to the technical field of packaging films, and discloses the following steps: firstly, using white hedyotis diffusa and citric acid as raw materials, multifunctional carbon dots are synthesized through a one-step hydrothermal method, and the carbon dots are uniformly dispersed in a gelatin / chitosan-based film. After the carbon dots are added, the prepared packaging film not only exhibits excellent antioxidant, antibacterial, ultraviolet-proof and pH response performances, but also has a significantly enhanced mechanical strength. The intelligent packaging film has environmental protection characteristics, helps to reduce environmental pollution, and can realize the monitoring function of the freshness of pork.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of packaging film, in particular to a preparation method of intelligent packaging film based on multifunctional novel carbon dot gelatin chitosan. BACKGROUND

[0002] With the improvement of living quality, the public's attention to food safety has gradually increased. Food packaging plays a crucial role in extending the shelf life of food and protecting its nutritional components. The current commonly used food packaging materials are mostly petroleum-derived polymers, which are difficult to degrade, leading to serious environmental problems and failing to meet environmental standards. At the same time, it is also difficult to monitor the quality change of food during storage. Therefore, there is an urgent need to develop a new type of intelligent packaging material based on natural biological materials that can indicate the freshness of food.

[0003] Carbon dots, as an innovative carbon nanomaterial with a size less than 10 nanometers, have good antioxidant, antibacterial properties, biocompatibility, and ultraviolet shielding ability. In addition, it can be used as a pH sensor, so it is an ideal additive for preparing multifunctional biological composite material films. In recent years, intelligent packaging technology based on biological polymers and carbon dots has attracted widespread attention. On the one hand, the antioxidant and antibacterial properties of carbon dots can effectively extend the shelf life of food and maintain food quality; on the other hand, carbon dots can change the fluorescence intensity according to the change of pH, that is, the freshness of food can be quickly distinguished. This visual, rapid, accurate and non-destructive food freshness discrimination technology has become the research focus in the field of intelligent packaging materials. Resveratrol is an endogenous non-flavonoid polyphenol with anti-inflammatory, antioxidant and anticancer effects. However, due to its low water solubility, poor absorption capacity, limited bioavailability and easy decomposition, the widespread application in practical application has been limited. Therefore, it is necessary to improve its water solubility and stability.

[0004] Using natural biodegradable substances to prepare biodegradable and edible new packaging materials has the advantages of convenient material acquisition, environmental protection, and diverse functions. Gelatin has excellent film-forming properties, excellent safety and moisture resistance. However, gelatin does not exhibit antibacterial, antioxidant or ultraviolet (UV) shielding properties. Chitosan has attracted widespread attention due to its excellent antibacterial activity, non-toxicity, biodegradability and biocompatibility. The complementary properties of gelatin and chitosan can be combined to produce films that can significantly improve the overall performance. However, the antibacterial and antioxidant activity of unmodified gelatin / chitosan films is still limited and cannot meet the requirements of long-term food preservation. Therefore, it is necessary to develop new, multifunctional, safe food packaging materials. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art packaging material technology, and provides a preparation method of a smart packaging film based on a multifunctional new carbon dot gelatin chitosan base, which takes gelatin and chitosan as a matrix and multifunctional carbon dots as a fluorescence intensity indicator, can increase the mechanical properties of the film while endowing the film with antibacterial, antioxidant and ultraviolet protection capabilities, and can monitor the freshness degree of pork according to the fluorescence intensity of the film.

[0006] To solve the problems in the background art, the present application adopts the following technical scheme: the specific steps are as follows:

[0007] Step one, preparation of multifunctional carbon dots: 0.2-0.7g of white propylphenol and 0.5-1.5g of citric acid are mixed and dissolved in deionized water, the temperature is 100℃, ultrasonic treatment is carried out in deionized water for 25-35min, then the mixed solution is poured into polytetrafluoroethylene, heated to 150-220℃ in an oven, heated for 4-9h, the temperature is reduced to 20-30℃, the precipitate is removed by centrifugation, the supernatant is loaded into a dialysis bag, and after dialysis and freeze-drying, white propylphenol-derived carbon dots are obtained;

[0008] Step two, preparation of gelatin / chitosan-based coating film: 5-15g of gelatin is dissolved in deionized water, heated to 40-60℃ in a magnetic stirrer, stirred for 0.5-1.5h at a speed of 800r / min, at the same time, chitosan is mixed with acetic acid solution, heated to 70-90℃ in a magnetic stirrer, stirred for 0.5-1.5h at a speed of 800r / min, then the stirred gelatin solution and the stirred chitosan solution are mixed to obtain a mixed solution of gelatin and chitosan;

[0009] Step three, preparation of multifunctional smart active packaging film: the white propylphenol-derived carbon dots prepared in step one are dispersed in the mixed solution of gelatin and chitosan in step two, stirred in a magnetic stirrer at a temperature of 40-60℃ for 1.5-2.5h, then glycerol is added as a plasticizer, and finally the mixed solution is poured onto a glass plate and naturally dried for 45-50h to obtain a multifunctional smart active packaging film.

[0010] In the preparation of white propylphenol-derived carbon dots in step one, the concentration of white propylphenol is 5mg / mL, the concentration of citric acid is 10mg / mL, the power of the oven ultrasonic is 70-100W, and the centrifugation rate is 12000r / min.

[0011] In step one, the molecular weight of the dialysis bag is 5000Da, the dialysis time is 45-50h, the freeze-drying temperature is-30--70℃, and the freeze-drying time is 45-50h.

[0012] The concentration of gelatin in the second step is 50-100 mg / mL, the concentration of chitosan is 50-100 mg / mL, and the concentration of acetic acid solution is 1%-2%.

[0013] The heating temperature of the gelatin solution in the second step is 50 DEG C, the heating temperature of the chitosan solution is 80 DEG C, and the rotating speed of the magnetic stirrer is 800 r / min.

[0014] In the second step, the stirred gelatin solution and the stirred chitosan solution are mixed, and the mixture is continuously stirred for 0.5-1.5 h.

[0015] In the third step, the resveratrol-derived carbon dots prepared in the first step are dispersed in the mixed gelatin and chitosan solution in the second step, and the concentration of the carbon dots is 0.5%-2%.

[0016] In the third step, the rotating speed of the magnetic stirrer is 800 r / min, the heating temperature is 50 DEG C, and the stirring time is 2 h.

[0017] In the third step, the plasticizer used is glycerol with a concentration of 1%.

[0018] In the third step, the drying time is 48 h, the storage is at 25 DEG C and 50% relative humidity, the tensile strength is 50-66 MPa, and the contact angle is >= 95 DEG.

[0019] The present application has the advantages of antibacterial, antioxidant, anti-ultraviolet and pH response functions, and can be used to extend the shelf life of food and indicate the freshness of pork. The addition of resveratrol-derived carbon dots in the present application significantly improves the antioxidant, antibacterial and mechanical properties of the film, and the film inherits the pH response function of the carbon dots, which can indicate the freshness of food, and greatly improves the comprehensive performance of the prepared food packaging film.

[0020] Specifically:

[0021] 1. The intelligent active packaging provided by the present application has a tensile property of 50 Mpa or more, a water contact angle of >= 95 DEG, good mechanical properties, a tensile strength of 66.78%, and a breaking elongation of 80.21%, effectively improving the poor mechanical properties of the gelatin / chitosan-based film.

[0022] 2. The multifunctional intelligent film prepared has good antibacterial properties against E. coli and Staphylococcus aureus, and when the carbon dot addition amount is 1.5%, the antibacterial rate of the film against Staphylococcus aureus is 82.36% and 90.37% respectively, which can effectively extend the shelf life of food.

[0023] 3. The multifunctional intelligent film prepared has good antioxidant and ultraviolet resistance, and when the carbon dot addition amount is 1.5%, the DPPH and ABTS removal rates are 64.56% and 92.30% respectively, which can effectively prevent the oxidation and color change of pork during storage.

[0024] 4. The multifunctional intelligent film prepared can change the fluorescence intensity according to the change of the pH of pork, and can be used to indicate the freshness of pork.

[0025] 5. The preparation process of the present application is simple, reproducible, and the prepared film is green and environmentally friendly, which is conducive to large-scale production and provides a new idea for the development of intelligent active packaging. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The film diagram of the control example and examples 1-4;

[0027] Figure 2 The mechanical strength comparison diagram of the control example and examples 1-4;

[0028] Figure 3 The antibacterial rate comparison diagram of the control example and examples 1-4;

[0029] Figure 4 The antioxidant performance comparison diagram of the control example and examples 1-4;

[0030] Figure 5 The ultraviolet resistance comparison diagram of the control example and examples 1-4;

[0031] Figure 6 The change diagram of the pH value of pork during storage;

[0032] Figure 7 The response diagram of example 3 with the change of the pH of pork. DETAILED DESCRIPTION

[0033] With reference to the drawings, the present application specifically adopts the following implementation manner: the specific steps are as follows:

[0034] Step one, preparing multifunctional carbon dots: 0.2-0.7g of white wine and 0.5-1.5g of citric acid are mixed and dissolved in deionized water, the temperature is 100℃, ultrasonic treatment is carried out in deionized water for 25-35min, then the mixed solution is poured into polytetrafluoroethylene, heated to 150-220℃ in an oven, heated for 4-9h, the temperature is reduced to 20-30℃, the precipitate is removed by centrifugation, and the supernatant is loaded into a dialysis bag, and after dialysis and freeze-drying, white wine derived carbon dots are obtained;

[0035] Step two, preparation of gelatin / chitosan-based coating film: 5-15 g of gelatin was dissolved in deionized water, heated to 40-60°C in a magnetic stirrer, and stirred for 0.5-1.5 h at a speed of 800 r / min, while chitosan was mixed with acetic acid solution, heated to 70-90°C in a magnetic stirrer, and stirred for 0.5-1.5 h at a speed of 800 r / min, then the stirred gelatin solution and the stirred chitosan solution were mixed to obtain a mixed solution of gelatin and chitosan;

[0036] Step three, preparation of multifunctional intelligent active packaging film: the resveratrol-derived carbon dots prepared in step one were dispersed in the mixed solution of gelatin and chitosan in step two, stirred in a magnetic stirrer at a temperature of 40-60°C for 1.5-2.5 h, then glycerol was added as a plasticizer, and finally the mixed solution was poured onto a glass plate and naturally dried for 45-50 h to obtain a multifunctional intelligent active packaging film.

[0037] In the preparation of resveratrol-derived carbon dots in step one, the concentration of resveratrol was 5 mg / mL and the concentration of citric acid was 10 mg / mL; the power of the ultrasonic oven was 70-100 W and the centrifugal speed was 12000 r / min. In step one, the molecular weight of the dialysis bag was 5000 Da, the dialysis time was 45-50 h, the freeze-drying temperature was -30 to -70°C, and the freeze-drying time was 45-50 h. In step two, the concentration of gelatin was 50-100 mg / mL, the concentration of chitosan was 50-100 mg / mL, and the concentration of acetic acid solution was 1%-2%. In step two, the heating temperature of the gelatin solution was 50°C and the heating temperature of the chitosan solution was 80°C, and the speed of the magnetic stirrer was 800 r / min. In step two, the stirred gelatin solution and the stirred chitosan solution were mixed and continued to be stirred for 0.5-1.5 h after mixing. In step three, the resveratrol-derived carbon dots prepared in step one were dispersed in the mixed solution of gelatin and chitosan in step two, and the concentration of the carbon dots was 0.5%-2%. In step three, the speed of the magnetic stirrer was 800 r / min, the heating temperature was 50°C, and the stirring time was 2 h. In step three, the plasticizer used was glycerol with a concentration of 1%. In step three, the drying time was 48 h, the storage was at 25°C and 50% relative humidity, the tensile strength was 50-66 MPa, and the contact angle was ≧95°.

[0038] Referring to Figure 6 and Figure 7 , the pH value of pork will also rise with the extension of storage time, and the fluorescence intensity of the film will decrease with the rise of pH value, so as to indicate the freshness of pork.

[0039] The thin film has three components, one is gelatin, one is chitosan, and the other is added carbon dots. Chitosan itself has a certain antibacterial effect, but the effect is not significant, and the main role is played by the added carbon dots.

[0040] The application will be further described below in conjunction with the accompanying drawings: Embodiment

[0041] A preparation method of a multifunctional novel carbon dot gelatin / chitosan-based intelligent packaging film is as follows:

[0042] Step one: 0.5g of white resveratrol and 1g of citric acid are dissolved in 100mL of deionized water (temperature 100℃) and ultrasonically treated for 30min, then the mixed solution is poured into polytetrafluoroethylene, heated in an oven at 200℃ for 8h. Remove the precipitate by centrifugation at 12000r / min, and then put the supernatant into a dialysis bag with a molecular weight of 5000Da and dialyze for 48h, then put it in a refrigerator at-80℃ for 12h, freeze-dry at-50℃, and after 48h of freeze-drying, white resveratrol derivative carbon dots are obtained.

[0043] Step two: 10g of gelatin (240 Bloom) is dissolved in 200mL of deionized water and stirred at 800r / min in a magnetic stirrer at 50℃ for 1h. In addition, 5g of chitosan (viscosity 200-800 Pas) is dissolved in 100mL of 1% acetic acid solution and continuously stirred at 800r / min in a magnetic stirrer at 80℃ for 1h. Then, the gelatin solution and chitosan solution are mixed.

[0044] Step three: 1.5g of white resveratrol derivative carbon dots prepared in step one are dispersed in the mixed solution of gelatin and chitosan, and stirred at 800r / min in a magnetic stirrer at 50℃ for 2h, then 3ml of glycerol is added. Pour the mixed solution onto a glass plate and naturally dry for 48h to obtain a multifunctional intelligent active packaging film. Embodiment

[0045] A preparation method of a multifunctional novel carbon dot gelatin / chitosan-based intelligent packaging film is as follows:

[0046] Step one: 0.5g of white resveratrol and 1g of citric acid are dissolved in 100mL of deionized water (temperature 100℃) and ultrasonically treated for 30min, then the mixed solution is poured into polytetrafluoroethylene, heated in an oven at 200℃ for 8h. Remove the precipitate by centrifugation at 12000r / min, and then put the supernatant into a dialysis bag with a molecular weight of 5000Da and dialyze for 48h, then put it in a refrigerator at-80℃ for 12h, freeze-dry at-50℃, and after 48h of freeze-drying, white resveratrol derivative carbon dots are obtained.

[0047] Step 2: Dissolve 10g of gelatin (240 Bloom) in 200mL of deionized water and stir at 800rpm in a magnetic stirrer at 50°C for 1 hour. Separately, dissolve 5g of chitosan (viscosity 200-800 Pas) in 100mL of 1% acetic acid solution and stir continuously at 800rpm in a magnetic stirrer at 80°C for 1 hour. Then, mix the gelatin and chitosan solutions.

[0048] Step 3: Disperse 3g of the resveratrol-derived carbon dots prepared in Step 1 into a mixed solution of gelatin and chitosan. Stir the mixture at 800 rpm in a magnetic stirrer at 50°C for 2 hours. Then, add 3ml of glycerol. Pour the mixture onto a glass plate and air-dry for 48 hours to obtain a multifunctional smart active packaging film. Example

[0049] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows:

[0050] Step 1: Dissolve 0.5g of resveratrol and 1g of citric acid in 100mL of deionized water (100°C) and sonicate for 30 minutes. The mixture is then poured into a polytetrafluoroethylene container and heated in an oven at 200°C for 8 hours. Centrifuge at 12,000 rpm to remove the precipitate. The supernatant is then placed in a 5,000Da dialysis bag and dialyzed for 48 hours. The solution is then placed in a -80°C freezer for 12 hours and freeze-dried at -50°C for 48 hours to yield resveratrol-derived carbon dots.

[0051] Step 2: Dissolve 10g of gelatin (240Bloom) in 200mL of deionized water and stir at 800rpm in a magnetic stirrer at 50°C for 1 hour. Separately, dissolve 5g of chitosan (viscosity 200-800 Pas) in 100mL of 1% acetic acid solution and stir continuously at 800rpm in a magnetic stirrer at 80°C for 1 hour. Then, mix the gelatin and chitosan solutions.

[0052] Step 3: Disperse 4.5g of the resveratrol-derived carbon dots prepared in Step 1 into a mixed solution of gelatin and chitosan. Stir the mixture at 800 rpm in a magnetic stirrer at 50°C for 2 hours. Then, add 3ml of glycerol. Pour the mixture onto a glass plate and air-dry for 48 hours to obtain a multifunctional smart active packaging film. Example

[0053] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows:

[0054] Step 1: 0.5 g of resveratrol and 1 g of citric acid were dissolved in 100 mL of deionized water (temperature 100°C) under ultrasonic for 30 min, and then the mixed solution was poured into polytetrafluoroethylene, heated in an oven at 200°C for 8 h. The precipitate was removed by centrifugation at 12000 r / min, and the supernatant was loaded into a dialysis bag with a molecular weight of 5000 Da for dialysis for 48 h, then placed in a refrigerator at -80°C for 12 h, and freeze-dried at -50°C for 48 h to obtain resveratrol-derived carbon dots.

[0055] Step 2: 10 g of gelatin (240 Bloom) was dissolved in 200 mL of deionized water, stirred at 800 r / min in a magnetic stirrer at 50°C for 1 h. In addition, 5 g of chitosan (viscosity 200-800 Pas) was dissolved in 100 mL of 1% acetic acid solution, continuously stirred at 800 r / min in a magnetic stirrer at 80°C for 1 h. Then, the gelatin solution and chitosan solution were mixed.

[0056] Step 3: 4.5 g of resveratrol-derived carbon dots prepared in step 1 were dispersed in the mixed solution of gelatin and chitosan, stirred at 800 r / min in a magnetic stirrer at 50°C for 2 h, and then 3 ml of glycerol was added. The mixed solution was poured onto a glass plate and naturally dried for 48 h to obtain a multifunctional intelligent active packaging film.

[0057] Comparative Example

[0058] Preparation of gelatin / chitosan-based film

[0059] 10 g of gelatin (240 Bloom) was dissolved in 200 mL of deionized water, stirred at 800 r / min in a magnetic stirrer at 50°C for 1 h. In addition, 5 g of chitosan (viscosity 200-800 Pas) was dissolved in 100 mL of 1% acetic acid solution, continuously stirred at 800 r / min in a magnetic stirrer at 80°C for 1 h. Then, the gelatin solution and chitosan solution were mixed, stirred at 800 r / min in a magnetic stirrer at 50°C for 2 h, and then 3 ml of glycerol was added. The mixed solution was poured onto a glass plate and naturally dried for 48 h to obtain a gelatin / chitosan-based film.

[0060] The multifunctional novel carbon dots prepared in Examples 1-4 and the gelatin / chitosan-based film obtained in Comparative Example 1 were tested for antibacterial ability.

[0061] I. Test method of antibacterial flat plate experiment

[0062] The antibacterial ability of the films was evaluated by measuring the number of colonies after direct contact with the films. The films of Examples 1-4 and the control group were irradiated with UV light for 30 min, and Staphylococcus aureus or Escherichia coli was cultured in a liquid medium (Luria-Bertani) at 37°C for 24 h. The OD value of the bacterial suspension was adjusted to 0.1 at 600 nm, and then diluted 100-fold. Then, 1 mL of the bacterial solution was added to the 96-well plate containing the films of Examples 1-4 and the control group. After co-culturing at 37°C for 24 h, the OD value of each group was measured, and the antibacterial rate was calculated according to the following formula:

[0063] OD600-1 refers to the OD value at 600 nm after the Example group and the control group were co-incubated with bacteria for 24 h, and OD600-2 is the OD value at 600 nm of the blank experiment (bacteria cultured for 24 h).

[0064] (1− OD600-1 / OD600-2) × 100% (1)

[0065] II. Antioxidant performance test method

[0066] 50 mg of the films of Examples 1-4 and the control group were added to 10 mL of DPPH or ABTS solution, and the absorbance value was 0.7 ± 0.02. After reacting in the dark for 30 min, the absorbance was measured at 515 or 734 nm.

[0067] (A1− A2) / A1 × 100% (2)

[0068] where A1 and A2 represent the absorbance values at 515 nm / 734 nm of the blank control and the control group, respectively.

[0069] According to the above formula, the clearance rate corresponding to the absorbance value:

[0070] The DPPH clearance rate corresponds to the value:

[0071] Control group: A1 = 0.699, A2 = 0.336, A2 = 0.332, A2 = 0.335, average A2 = 0.610, DPPH clearance rate = 12.73%.

[0072] Example 1: A1 = 0.699, A2 = 0.338, A2 = 0.334, A2 = 0.337, average A2 = 0.336, DPPH clearance rate = 51.93%.

[0073] Example 2: A1 = 0.699, A2 = 0.298, A2 = 0.300, A2 = 0.297, average A2 = 0.298, DPPH clearance rate = 57.37%.

[0074] Example 3: A1=0.699, A2=0.247, A2=0.246, A2=0.248, average A2=0.247, the clearance rate of DPPH is 64.66%.

[0075] Example 4: A1=0.699, A2=0.241, A2=0.243, A2=0.239, average A2=0.241, the clearance rate of DPPH is 65.52%.

[0076] According to the above formula, the ABTS clearance rate corresponds to the value:

[0077] Control group: A1=0.701, A2=0.537, A2=0.561, A2=0.562, average A2=0.553, the clearance rate of ABTS is 21.13%.

[0078] Example 1: A1=0.701, A2=0.348, A2=0.352, A2=0.349, average A2=0.350, the clearance rate of ABTS is 50.07%.

[0079] Example 2: A1=0.701, A2=0.147, A2=0.140, A2=0.145, average A2=0.144, the clearance rate of ABTS is 79.46%.

[0080] Example 3: A1=0.701, A2=0.050, A2=0.056, A2=0.056, average A2=0.054, the clearance rate of ABTS is 92.30%.

[0081] Example 4: A1=0.701, A2=0.048, A2=0.049, A2=0.052, average A2=0.050, the clearance rate of ABTS is 92.88%.

[0082] The application provides a gelatin / chitosan-based intelligent active packaging film based on multifunctional carbon dots, which is green, environmentally friendly and degradable, and has excellent antibacterial, antioxidant, ultraviolet-proof and pH-responsive functions. The film can effectively prolong the shelf life of products and detect the freshness of food.

[0083] In summary, the preparation method of the intelligent packaging film based on the multifunctional novel carbon dot gelatin chitosan base has antibacterial, antioxidant, ultraviolet-proof and pH-responsive functions, and can be used to prolong the shelf life of food and indicate the freshness of pork. The addition of resveratrol-derived carbon dots in the application significantly improves the antioxidant property, antibacterial property and mechanical property of the film, and the film inherits the pH-responsive function of carbon dots, which can indicate the freshness of food, and greatly improves the comprehensive performance of the prepared food packaging film.

Claims

1. A method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film, characterized in that: The specific steps are as follows: Step 1: Preparation of multifunctional carbon dots: 0.2-0.7 g of resveratrol and 0.5-1.5 g of citric acid were mixed and dissolved in deionized water at 100°C, and ultrasonicated in deionized water for 25-35 min. The mixed solution was then poured into polytetrafluoroethylene and heated in an oven to 150-220°C for 4-9 h. The temperature was then lowered to 20-30°C and centrifuged to remove the precipitate. The supernatant was placed in a dialysis bag, dialyzed, and freeze-dried to obtain resveratrol-derived carbon dots. Step 2: preparing a gelatin / chitosan-based coating: dissolving 5-15 g of gelatin in deionized water, heating the mixture to 40-60° C. in a magnetic stirrer, stirring for 0.5-1.5 h at a speed of 800 r / min, and at the same time, mixing chitosan with an acetic acid solution, heating the mixture to 70-90° C. in a magnetic stirrer, stirring for 0.5-1.5 h at a speed of 800 r / min, and then mixing the stirred gelatin solution and the stirred chitosan solution to obtain a mixed solution of gelatin and chitosan; Step 3: Preparing a multifunctional smart active packaging film: dispersing the resveratrol-derived carbon dots prepared in step 1 in the mixed solution of gelatin and chitosan prepared in step 2, stirring the mixture in a magnetic stirring pot at a temperature of 40-60°C for 1.5-2.5 hours, then adding plasticizer glycerol, and finally pouring the mixed solution onto a glass plate and naturally drying it for 45-50 hours to obtain a multifunctional smart active packaging film; In the step three, the resveratrol-derived carbon dots prepared in the step one are dispersed in the gelatin and chitosan mixed solution in the step two, wherein the concentration of the carbon dots is 0.5% to 2%.

2. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 1 for preparing resveratrol-derived carbon dots, the resveratrol concentration is 5 mg / mL, the citric acid concentration is 10 mg / mL, the ultrasonic power is 70-100 W, and the centrifugal speed is 12000 r / min.

3. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 1, the molecular weight of the dialysis bag is 5000 Da, the dialysis time is 45 to 50 hours, the freeze-drying temperature is -30 to -70°C, and the freeze-drying time is 45 to 50 hours.

4. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 2, the concentration of gelatin is 50-100 mg / mL, the concentration of chitosan is 50-100 mg / mL, and the concentration of acetic acid solution is 1%-2%.

5. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 2, the gelatin solution is heated to 50° C., the chitosan solution is heated to 80° C., and the speed of the magnetic stirrer is 800 r / min.

6. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 2, the stirred gelatin solution and the stirred chitosan solution are mixed, and the mixture is continued to be stirred for 0.5 to 1.5 hours.

7. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: In the step 3, the speed of the magnetic stirrer is 800 r / min, the heating temperature is 50° C., and the stirring time is 2 h.

8. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: The plasticizer used in the step 3 is glycerol with a concentration of 1%.

9. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based smart packaging film according to claim 1, characterized in that: The drying time in step 3 is 48 hours, and the product is stored at 25°C and 50% relative humidity. The tensile strength is 50-66 MPa and the contact angle is ≥95°.

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