Preparation method of intelligent packaging film based on multifunctional novel carbon dot gelatin chitosan base

Abstract

The invention discloses a preparation method of an intelligent packaging film based on a multifunctional novel carbon dot gelatin chitosan base, and relates to the technical field of packaging films.The method comprises the steps that resveratrol and citric acid serve as raw materials, multifunctional carbon dots are synthesized through a one-step hydrothermal method, and the carbon dots are evenly dispersed in a gelatin / chitosan base film; after the carbon dots are added, the prepared packaging film not only shows excellent antioxidant, antibacterial, ultraviolet-proof and pH-responsive properties, but also has significantly enhanced mechanical strength. The intelligent packaging film has the characteristic of environmental protection, is beneficial to reducing environmental pollution, and can realize the function of monitoring the freshness of pork.

Description

Technical Field

[0001] The invention relates to the technical field of packaging films, and in particular to a method for preparing a multifunctional novel carbon dot gelatin chitosan-based intelligent packaging film. Background Art

[0002] As the quality of life improves, the public's attention to food safety is gradually increasing. Food packaging plays a vital role in extending the shelf life of food and protecting its nutrients. Currently, the commonly used food packaging materials are mostly petroleum-derived polymer plastics, which are difficult to degrade, leading to serious environmental problems and unable to meet environmental standards. At the same time, it is also difficult to monitor the quality changes of food during storage. Therefore, there is an urgent need to develop an intelligent packaging material based on natural biomaterials that can indicate the freshness of food.

[0003] As an innovative carbon nanomaterial with a size of less than 10 nanometers, carbon dots have good antioxidant, antibacterial properties, biocompatibility, and UV shielding capabilities. In addition, it can be used as a pH sensor, so it is an ideal additive for preparing multifunctional biocomposite films. In recent years, smart packaging technology based on biopolymers and carbon dots has received 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 acid-base changes, which can quickly identify the freshness of food. This visual, fast, accurate and non-destructive food freshness identification technology has become a research focus in the field of smart packaging materials. Resveratrol is an endogenous non-flavonoid polyphenol with anti-inflammatory, antioxidant and anti-cancer effects. However, due to its low water solubility, poor absorption capacity, limited bioavailability and easy decomposition, the wide application of resveratrol in practical applications is limited. Therefore, it is necessary to improve its water solubility and stability.

[0004] The use of natural biodegradable substances to prepare new biodegradable and edible 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 significantly improve overall performance. However, the antibacterial and antioxidant activities of unmodified gelatin / chitosan films are still limited and cannot meet the requirements of long-term food preservation. Therefore, new, multifunctional, and safe food packaging materials must be developed. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of existing packaging material technology and to provide a method for preparing an intelligent packaging film based on a multifunctional novel carbon dot gelatin chitosan. The method uses gelatin and chitosan as a matrix and multifunctional carbon dots as a fluorescence intensity indicator. While giving the film antibacterial, antioxidant and UV protection capabilities, it increases the mechanical properties of the film and can monitor the freshness of pork according to the fluorescence intensity of the film.

[0006] In order to solve the problems existing in the background technology, the present invention adopts the following technical solution: 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, heated to 150-220° C. in an oven for 4-9 h, and the temperature was 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 gelatin / chitosan-based coating: dissolving 5-15 g of gelatin in deionized water, heating to 40-60° C. in a magnetic stirrer, stirring for 0.5-1.5 h at a speed of 800 r / min, at the same time, mixing chitosan with acetic acid solution, heating 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: prepare a multifunctional intelligent active packaging film: disperse the resveratrol-derived carbon dots prepared in step 1 in the mixed solution of gelatin and chitosan in step 2, stir in a magnetic stirring pot at a temperature of 40-60°C for 1.5-2.5 hours, then add plasticizer glycerol, and finally pour the mixed solution onto a glass plate and dry naturally for 45-50 hours to obtain a multifunctional intelligent active packaging film.

[0007] In the step 1 for preparing resveratrol-derived carbon dots, the concentration of resveratrol is 5 mg / mL, the concentration of citric acid is 10 mg / mL; the power of the ultrasound in the oven is 70-100W, and the centrifugal speed is 12000r / min.

[0008] 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.

[0009] 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%.

[0010] In the step 2, the optimal heating temperature of the gelatin solution is 50° C., the optimal heating temperature of the chitosan solution is 80° C., and the speed of the magnetic stirrer is 800 r / min.

[0011] In the step 2, the stirred gelatin solution and the stirred chitosan solution are mixed, and the stirring is continued after mixing, and the stirring time is 0.5 to 1.5 hours.

[0012] In the step three, the resveratrol-derived carbon dots prepared in the step one are dispersed in the mixed solution of gelatin and chitosan in the step two, wherein the concentration of the carbon dots is 0.5% to 2%.

[0013] In the step 3, the rotation speed of the magnetic stirrer is 800 r / min, the heating temperature is optimally 50° C., and the stirring time is optimally 2 h.

[0014] The plasticizer used in the step 3 is glycerol with a concentration of 1%.

[0015] The optimal drying time in step 3 is 48 hours. When stored at 25°C and 50% relative humidity, the tensile strength is 50-66 MPa and the contact angle is ≧95°.

[0016] The beneficial effects of the present invention are: having antibacterial, antioxidant, UV protection 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 invention significantly improves the antioxidant, antibacterial and mechanical properties of the film. At the same time, the film inherits the pH response function of the carbon dots, can indicate the freshness of food, and greatly improves the comprehensive performance of the prepared food packaging film.

[0017] Specific: 1. The tensile properties of the smart active packaging provided by the present invention are above 50 Mpa, the water contact angle is ≧95°, and it has good mechanical properties, a tensile strength of 66.78%, and a breaking elongation of 80.21%, which effectively improves the problem of poor mechanical properties of gelatin / chitosan-based films.

[0018] 2. The prepared multifunctional smart film has good antibacterial properties against Escherichia coli and Staphylococcus aureus. When the carbon dot addition amount is 1.5%, the antibacterial rates of the film against Staphylococcus aureus are 82.36% and 90.37%, respectively, which can effectively extend the shelf life of food.

[0019] 3. The prepared multifunctional smart film has good antioxidant and UV resistance. 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 pork from oxidation and color changes during storage.

[0020] 4. The prepared multifunctional smart film can change the fluorescence intensity according to the change of pH of pork, and can be used to indicate the freshness of pork.

[0021] 5. The preparation process of the present invention is simple and has good repeatability. The prepared film is green and environmentally friendly, which is conducive to large-scale production and provides new ideas for the development of intelligent active packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The film diagrams of the control example and embodiments 1 to 4; Figure 2 It is a comparison diagram of the mechanical strength of the control example and embodiments 1 to 4; Figure 3 It is a comparison chart of the antibacterial rate of the control example and embodiments 1 to 4; Figure 4 It is a comparison chart of the antioxidant performance of the control example and Examples 1 to 4; Figure 5 It is a comparative diagram of the anti-ultraviolet rays of the control example and embodiments 1 to 4; Figure 6 This is a graph showing the changes in pH value of pork during storage; Figure 7 This is the response diagram of Example 3 as the pH of pork changes. DETAILED DESCRIPTION

[0023] With reference to the figures, the present invention specifically adopts the following implementation mode: 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, heated to 150-220° C. in an oven for 4-9 h, and the temperature was 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 gelatin / chitosan-based coating: dissolving 5-15 g of gelatin in deionized water, heating to 40-60° C. in a magnetic stirrer, stirring for 0.5-1.5 h at a speed of 800 r / min, at the same time, mixing chitosan with acetic acid solution, heating 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: prepare a multifunctional intelligent active packaging film: disperse the resveratrol-derived carbon dots prepared in step 1 in the mixed solution of gelatin and chitosan in step 2, stir in a magnetic stirring pot at a temperature of 40-60°C for 1.5-2.5 hours, then add plasticizer glycerol, and finally pour the mixed solution onto a glass plate and dry naturally for 45-50 hours to obtain a multifunctional intelligent active packaging film.

[0024] When preparing resveratrol-derived carbon dots in step 1, the concentration of resveratrol is 5 mg / mL, the concentration of citric acid is 10 mg / mL; the power of the ultrasound in the oven is 70-100W, and the centrifugal speed is 12000r / min. In step 1, the molecular weight of the dialysis bag is 5000 Da, the dialysis time is 45-50h, the freeze-drying temperature is -30--70℃, and the freeze-drying time is 45-50h. In 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%. In step 2, the best heating temperature of the gelatin solution is 50℃, the best heating temperature of the chitosan solution is 80℃, and the speed of the magnetic stirrer is 800r / min. In step 2, the stirred gelatin solution and the stirred chitosan solution are mixed, and stirring is continued after mixing, and the stirring time is 0.5-1.5h. In the step 3, the resveratrol-derived carbon dots prepared in step 1 are dispersed in the gelatin and chitosan mixed solution in step 2, wherein the concentration of the carbon dots is 0.5% to 2%. In the step 3, the speed of the magnetic stirrer is 800 r / min, the heating temperature is optimally 50°C, and the stirring time is optimally 2h. The plasticizer used in the step 3 is 1% glycerol. In the step 3, the drying time is optimally 48h, and when stored at 25°C and 50% relative humidity, the tensile strength is 50 to 66MPa, and the contact angle is ≧95°.

[0025] Reference Figure 6 and Figure 7 As the storage time of pork increases, its pH value will also increase, and the fluorescence intensity of the film will decrease as the pH value increases, thereby indicating the freshness of the pork.

[0026] The 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 added carbon dots play a major role.

[0027] The present invention will be further described below in conjunction with the accompanying drawings: Example

[0028] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows: Step 1: Dissolve 0.5g resveratrol and 1g citric acid in 100mL deionized water (temperature 100℃) and ultrasonicate for 30min, then pour the mixed solution into polytetrafluoroethylene and heat it in an oven at 200℃ for 8h. Centrifuge at 12000r / min to remove the precipitate, and place the supernatant into a dialysis bag with a molecular weight of 5000Da for 48h, then place it in a refrigerator at -80℃ for 12h, freeze-dry at -50℃, and freeze-dry for 48h to obtain resveratrol-derived carbon dots.

[0029] Step 2: Dissolve 10g of gelatin (240Bloom) in 200mL of deionized water and stir at 800r / min for 1h in a magnetic stirrer at 50℃. Separately, dissolve 5g of chitosan (viscosity 200-800 Pas) in 100mL of 1% acetic acid solution and stir continuously at 800r / min for 1h in a magnetic stirrer at 80℃. Then, mix the gelatin solution and the chitosan solution.

[0030] Step 3: Disperse 1.5 g of the resveratrol-derived carbon dots prepared in step 1 in a mixed solution of gelatin and chitosan, stir at 800 r / min for 2 h in a magnetic stirring pot at 50 °C, and then add 3 ml of glycerol. Pour the mixed solution onto a glass plate and dry it naturally for 48 h to obtain a multifunctional smart active packaging film. Example

[0031] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows: Step 1: Dissolve 0.5g resveratrol and 1g citric acid in 100mL deionized water (temperature 100℃) and ultrasonicate for 30min, then pour the mixed solution into polytetrafluoroethylene and heat it in an oven at 200℃ for 8h. Centrifuge at 12000r / min to remove the precipitate, and place the supernatant into a dialysis bag with a molecular weight of 5000Da for 48h, then place it in a refrigerator at -80℃ for 12h, freeze-dry at -50℃, and freeze-dry for 48h to obtain resveratrol-derived carbon dots.

[0032] Step 2: Dissolve 10 g of gelatin (240 Bloom) in 200 mL of deionized water and stir at 800 r / min for 1 h in a magnetic stirrer at 50°C. Separately, dissolve 5 g of chitosan (viscosity 200-800 Pas) in 100 mL of 1% acetic acid solution and stir continuously at 800 r / min for 1 h in a magnetic stirrer at 80°C. Then, mix the gelatin solution and the chitosan solution.

[0033] Step 3: Disperse 3 g of the resveratrol-derived carbon dots prepared in step 1 in a mixed solution of gelatin and chitosan, stir at 800 r / min for 2 h in a magnetic stirring pot at 50°C, and then add 3 ml of glycerol. Pour the mixed solution onto a glass plate and dry it naturally for 48 h to obtain a multifunctional smart active packaging film. Example

[0034] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows: Step 1: Dissolve 0.5g resveratrol and 1g citric acid in 100mL deionized water (temperature 100℃) and ultrasonicate for 30min, then pour the mixed solution into polytetrafluoroethylene and heat it in an oven at 200℃ for 8h. Centrifuge at 12000r / min to remove the precipitate, and place the supernatant into a dialysis bag with a molecular weight of 5000Da for 48h, then place it in a refrigerator at -80℃ for 12h, freeze-dry at -50℃, and freeze-dry for 48h to obtain resveratrol-derived carbon dots.

[0035] Step 2: Dissolve 10g of gelatin (240Bloom) in 200mL of deionized water and stir at 800r / min for 1h in a magnetic stirrer at 50℃. In addition, dissolve 5g of chitosan (viscosity 200-800Pas) in 100mL of 1% acetic acid solution and stir continuously at 800r / min for 1h in a magnetic stirrer at 80℃. Then, mix the gelatin solution and the chitosan solution.

[0036] Step 3: Disperse 4.5 g of the resveratrol-derived carbon dots prepared in step 1 in a mixed solution of gelatin and chitosan, stir at 800 r / min for 2 h in a magnetic stirring pot at 50 °C, and then add 3 ml of glycerol. Pour the mixed solution onto a glass plate and dry it naturally for 48 h to obtain a multifunctional smart active packaging film. Example

[0037] A method for preparing a multifunctional novel carbon dot gelatin / chitosan-based smart packaging film, the specific steps are as follows: Step 1: Dissolve 0.5g resveratrol and 1g citric acid in 100mL deionized water (temperature 100℃) and ultrasonicate for 30min, then pour the mixed solution into polytetrafluoroethylene and heat it in an oven at 200℃ for 8h. Centrifuge at 12000r / min to remove the precipitate, and place the supernatant into a dialysis bag with a molecular weight of 5000Da for 48h, then place it in a refrigerator at -80℃ for 12h, freeze-dry at -50℃, and freeze-dry for 48h to obtain resveratrol-derived carbon dots.

[0038] Step 2: Dissolve 10g of gelatin (240Bloom) in 200mL of deionized water and stir at 800r / min for 1h in a magnetic stirrer at 50℃. In addition, dissolve 5g of chitosan (viscosity 200-800Pas) in 100mL of 1% acetic acid solution and stir continuously at 800r / min for 1h in a magnetic stirrer at 80℃. Then, mix the gelatin solution and the chitosan solution.

[0039] Step 3: Disperse 4.5 g of the resveratrol-derived carbon dots prepared in step 1 in a mixed solution of gelatin and chitosan, stir at 800 r / min for 2 h in a magnetic stirring pot at 50 °C, and then add 3 ml of glycerol. Pour the mixed solution onto a glass plate and dry it naturally for 48 h to obtain a multifunctional smart active packaging film.

[0040] Comparison Example Preparation of gelatin / chitosan-based films 10 g of gelatin (240 Bloom) was dissolved in 200 mL of deionized water and stirred at 800 r / min for 1 h in a magnetic stirrer at 50 °C. In addition, 5 g of chitosan (viscosity 200-800 Pas) was dissolved in 100 mL of 1% acetic acid solution and stirred continuously at 800 r / min for 1 h in a magnetic stirrer at 80 °C. Then, the gelatin solution and the chitosan solution were mixed, stirred at 800 r / min for 2 h in a magnetic stirring pot at 50 °C, and then 3 ml of glycerol was added. The mixed solution was poured onto a glass plate and dried naturally for 48 h to obtain a gelatin / chitosan-based film.

[0041] The antibacterial ability of the intelligent active packaging of the multifunctional novel carbon dots prepared in Examples 1 to 4 and the gelatin / chitosan-based film obtained in Control Example 1 was tested.

[0042] 1. Antibacterial plate test method The antibacterial ability of the film was evaluated by measuring the number of colonies after direct contact with the film. The films of Examples 1-4 and the control group were irradiated with ultraviolet light for 30 minutes, and Staphylococcus aureus or Escherichia coli were cultured in a liquid culture medium (Luria-Bertani) at 37°C for 24 hours. The OD value of the bacterial suspension was adjusted to 0.1 at 600nm and then diluted 100 times. Then, 1mL of the bacterial solution was added to a 96-well plate (containing the films of Examples 1-4 and the control example) and the OD value of each group was measured after co-culture at 37°C for 24 hours. The antibacterial rate was calculated as follows: OD600-1 refers to the OD value at 600 nm of the example group and the control group after incubation with bacteria for 24 h, and OD600-2 refers to the OD value at 600 nm of the blank experiment (bacterial incubation for 24 h).

[0043] (1− OD600-1 / OD600-2)×100% (1) 2. Antioxidant performance test method 50 mg of the film of Examples 1-4 and the control group were added to 10 mL of DPPH or ABTS solution, respectively, and the absorbance value was 0.7±0.02. After reacting in the dark for 30 minutes, the absorbance was measured at 515 or 734 m.

[0044] (A1 − A2) / A1 × 100% (2) Wherein A1 and A2 represent the absorbance values ​​of blank control and control example and embodiment at 515nm / 734nm respectively.

[0045] According to the above formula, the clearance rate corresponding to the absorbance value is: DPPH clearance corresponding value: Control group: A1=0.699, A2=0.336, A2=0.332, A2=0.335, average value A2=0.610, the DPPH clearance rate was 12.73%.

[0046] Example 1: A1=0.699, A2=0.338, A2=0.334, A2=0.337, average value A2=0.336, the DPPH removal rate is 51.93%.

[0047] Example 2: A1=0.699, A2=0.298, A2=0.300, A2=0.297, average value A2=0.298, the removal rate of DPPH is 57.37%.

[0048] Example 3: A1=0.699, A2=0.247, A2=0.246, A2=0.248, average value A2=0.247, the removal rate of DPPH is 64.66%.

[0049] Example 4: A1=0.699, A2=0.241, A2=0.243, A2=0.239, average value A2=0.241, the removal rate of DPPH is 65.52%.

[0050] According to the above formula, the corresponding value of ABTS clearance rate is: Control group: A1=0.701, A2=0.537, A2=0.561, A2=0.562, average value A2=0.553, the clearance rate of ABTS was 21.13%.

[0051] Example 1: A1=0.701, A2=0.348, A2=0.352, A2=0.349, average value A2=0.350, the clearance rate of ABTS is 50.07%.

[0052] Example 2: A1=0.701, A2=0.147, A2=0.140, A2=0.145, average value A2=0.144, the clearance rate of ABTS is 79.46%.

[0053] Example 3: A1=0.701, A2=0.050, A2=0.056, A2=0.056, average value A2=0.054, the clearance rate of ABTS is 92.30%.

[0054] Example 4: A1=0.701, A2=0.048, A2=0.049, A2=0.052, average value A2=0.050, the clearance rate of ABTS is 92.88%.

[0055] The present invention 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, UV protection and pH response functions. It can effectively extend the shelf life of the product and detect the freshness of the food.

[0056] In summary, the preparation method of the multifunctional novel carbon dot gelatin chitosan-based intelligent packaging film has antibacterial, antioxidant, UV protection 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 invention significantly improves the antioxidant, antibacterial and mechanical properties of the film. At the same time, the film inherits the pH response function of the carbon dots, which can indicate the freshness of the food and greatly improve the comprehensive performance of the prepared food packaging film.

Claims

1. A method for preparing a multifunctional novel carbon dot gelatin chitosan-based intelligent 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, heated to 150-220° C. in an oven for 4-9 h, and the temperature was 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 gelatin / chitosan-based coating: dissolving 5-15 g of gelatin in deionized water, heating to 40-60° C. in a magnetic stirrer, stirring for 0.5-1.5 h at a speed of 800 r / min, at the same time, mixing chitosan with acetic acid solution, heating 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: prepare a multifunctional intelligent active packaging film: disperse the resveratrol-derived carbon dots prepared in step 1 in the mixed solution of gelatin and chitosan in step 2, stir in a magnetic stirring pot at a temperature of 40-60°C for 1.5-2.5 hours, then add plasticizer glycerol, and finally pour the mixed solution onto a glass plate and dry naturally for 45-50 hours to obtain a multifunctional intelligent active packaging film.

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 concentration of resveratrol is 5 mg / mL, the concentration of citric acid is 10 mg / mL; the power of the ultrasound in the oven is 70-100W, and the centrifugal speed is 12000r / min.

3. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based intelligent 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 intelligent 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 intelligent packaging film according to claim 1, characterized in that: In the step 2, the optimal heating temperature of the gelatin solution is 50° C., the optimal heating temperature of the chitosan solution is 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 intelligent 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 stirring is continued after mixing, and the stirring time is 0.5 to 1.5 hours.

7. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based intelligent packaging film according to claim 1, characterized in that: In the step three, the resveratrol-derived carbon dots prepared in the step one are dispersed in the mixed solution of gelatin and chitosan in the step two, wherein the concentration of the carbon dots is 0.5% to 2%.

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

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

10. The method for preparing a multifunctional novel carbon dot gelatin chitosan-based intelligent packaging film according to claim 1, characterized in that: The optimal drying time in step 3 is 48 hours. When 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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