Carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid, food packaging film and preparation method and application of food fresh-keeping liquid and food packaging film

Abstract

The invention discloses carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid, a food packaging film as well as a preparation method and application of the food packaging film, and belongs to the field of food packaging materials. The food fresh-keeping liquid is characterized by comprising the following components in parts by weight: 0.1-1.5 parts of chitosan quaternary ammonium salt; 0.1 to 1.5 parts of gelatin; 0.01 to 0.2 part of carbon quantum dots; 97 to 99 parts of deionized water; the carbon quantum dots are prepared from edible natural raw materials through a hydrothermal method, and have good biocompatibility and safety; the food packaging film comprises the following components in parts by weight: 98-100 parts of the food fresh-keeping liquid; and 0-2 parts of glycerol. The invention also discloses a preparation method of the food fresh-keeping liquid and the food packaging film. The preparation method comprises the following steps: S1, preparing a chitosan quaternary ammonium salt solution; s2, preparing a gelatin solution; s3, preparing carbon quantum dots; s4, mixing the chitosan quaternary ammonium salt solution, the gelatin solution and the carbon quantum dots to prepare a food fresh-keeping solution; and S5, adding glycerol into the food fresh-keeping liquid, and drying to obtain the multifunctional active food packaging film. The carbon quantum dots not only have excellent oxidation resistance and ultraviolet absorption performance, but also can significantly improve the antibacterial property of food fresh-keeping liquid and food packaging films prepared from chitosan quaternary ammonium salt and gelatin. When the food packaging film is used for preserving cherries and tomatoes and the food preservation liquid is used for preserving litchis, the preservation time of fruits can be obviously prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid, a food packaging film and a preparation method and application thereof, and belongs to the field of food packaging materials. BACKGROUND

[0002] Food is rich in various nutrients, but during storage and transportation, it is prone to deterioration due to microbial contamination, oxidation and other factors, which not only reduces the edible value of the food, but also causes a large amount of food waste. Packaging food with packaging materials can block the influence of external adverse factors to a certain extent, prolong the preservation time of the food, and thus reduce waste.

[0003] Traditional plastic packaging materials have the advantages of light weight and low cost, but due to the lack of key active functions such as antibacterial, antioxidant, ultraviolet blocking and degradable, they are difficult to meet the requirements of modern food packaging in terms of prolonging the shelf life of food, ensuring food safety and environmental protection, and their application range is greatly limited.

[0004] Under this circumstance, it has become a research hotspot in this field to prepare packaging materials with active functions such as antibacterial and antioxidant by using natural degradable polymer compounds as substrates and adding active functional substances. Since food packaging materials are often in direct contact with food, they have very high safety requirements. Among them, natural edible substances with active functions have shown great application potential in the preparation of multifunctional food packaging materials due to their good biocompatibility and safety. For example, the patent (application number: 202411358441.9) of Nuna et al. discloses a packaging film prepared by using the extract of Saposhnikovia divaricata as an active ingredient. The film has certain antioxidant properties and can effectively inhibit the oxidation of food. The patent (application number: 202310817923.5) of Daxi Ren et al. reports that a preservative liquid is prepared by using chitosan, tea polyphenol and carvacrol as natural substances, and after being applied to the preservation of black-bone chicken meat, the oxidation and decay of the black-bone chicken meat are delayed, and the preservation period is prolonged.

[0005] However, natural edible substances with active functions have the disadvantages of single function and relatively few types, which greatly limits the further development and application of such food packaging materials. Therefore, it is an urgent need in the food industry and the field of material science to prepare substances with multiple active functions by using natural edible substances as raw materials, and then to prepare multifunctional food packaging materials. SUMMARY

[0006] The purpose of the present application is to solve the problems in the prior art, and a carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid and a food packaging film are disclosed. According to weight parts, the food preservative liquid comprises:

[0007] Chitosan quaternary ammonium salt: 0.1-1.5 parts;

[0008] Gelatin: 0.1-1.5 parts;

[0009] Carbon quantum dots: 0.01-0.2 parts;

[0010] Deionized water: 97-99 parts;

[0011] The carbon quantum dots are prepared by a hydrothermal method using edible natural raw materials and have good biocompatibility and safety;

[0012] The food packaging film comprises:

[0013] The above food fresh-keeping liquid: 98-100 parts;

[0014] Glycerol: 0-2 parts.

[0015] In some preferred embodiments, the carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid and food packaging film are characterized in that the carbon quantum dots not only have excellent antioxidant properties, but also can significantly improve the antibacterial, antioxidant and ultraviolet blocking properties of the food fresh-keeping liquid and packaging film made of chitosan quaternary ammonium salt and gelatin.

[0016] The application also discloses a preparation method of a carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid and food packaging film, and the steps are as follows:

[0017] S1: preparing a chitosan quaternary ammonium salt solution;

[0018] S2: preparing a gelatin solution;

[0019] S3: preparing carbon quantum dots;

[0020] S4: mixing the chitosan quaternary ammonium salt solution, the gelatin solution and the carbon quantum dots to prepare a food fresh-keeping liquid;

[0021] S5: adding glycerol to the food fresh-keeping liquid and drying to obtain a multifunctional active food packaging film.

[0022] In some preferred embodiments, the preparation method of the chitosan quaternary ammonium salt solution is as follows: chitosan quaternary ammonium salt is dissolved in deionized water, stirred at 50 DEG C for 2 h, and a chitosan quaternary ammonium salt solution is prepared.

[0023] In some preferred embodiments, the preparation method of the gelatin solution is as follows: gelatin is added to deionized water, stirred at 50 DEG C for 2 h, and a gelatin solution is prepared.

[0024] In some preferred embodiments, the preparation method of the carbon quantum dots is as follows: citric acid and citrulline are uniformly dispersed in deionized water, then transferred to a high-pressure reaction tube, and reacted under stirring and temperature control, then the product is filtered through a 0.22 μm filter membrane after cooling, then dialyzed in deionized water for 48 h, and then freeze-dried for standby.

[0025] The application also discloses application of the carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid and food packaging film in fruit and vegetable preservation.

[0026] The application uses natural edible citric acid and citrulline as raw materials, and prepares carbon quantum dots with excellent antioxidant capacity by a hydrothermal method, and then the carbon quantum dots are compounded with chitosan quaternary ammonium salt and gelatin to prepare multifunctional active food preservative liquid and food packaging film with antibacterial and antioxidant properties. The natural edible citric acid and citrulline do not have antioxidant capacity, but the carbon quantum dots prepared by the hydrothermal method have excellent antioxidant capacity. The raw materials are edible, and the preparation process is green, so that the obtained carbon quantum dots have good biocompatibility and safety. The carbon quantum dots prepared in the application not only have antioxidant and ultraviolet absorption properties, but also can enhance the antibacterial property of chitosan quaternary ammonium salt. Therefore, after the carbon quantum dots are added as active functional substances into the chitosan quaternary ammonium salt and gelatin composite film, the film is endowed with excellent antioxidant property and certain ultraviolet blocking capacity, and the antibacterial property of the composite film is significantly enhanced. The chitosan quaternary ammonium salt and gelatin composite film has the defects of weak ultraviolet blocking capacity, poor antioxidant capacity and weak antibacterial property. When the food packaging film is used for cherry tomato preservation, and the food preservative liquid is used for litchi preservation, the fruit preservation time can be obviously prolonged. Meanwhile, the carbon quantum dots, chitosan quaternary ammonium salt and gelatin synthesized in the application are edible materials, and can be directly contacted with food. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is an appearance diagram of the chitosan quaternary ammonium salt / gelatin / carbon quantum dot food packaging film

[0028] Figure 2 It is an ultraviolet transmittance diagram of the chitosan quaternary ammonium salt / gelatin / carbon quantum dot food packaging film

[0029] Figure 3 It is a DPPH free radical scavenging rate diagram of the chitosan quaternary ammonium salt / gelatin / carbon quantum dot food packaging film

[0030] Figure 4 It is a litchi preservation effect diagram of the chitosan quaternary ammonium salt / gelatin / carbon quantum dot preservative liquid packaging

[0031] Figure 5 It is a cherry tomato preservation effect diagram of the chitosan quaternary ammonium salt / gelatin / carbon quantum dot food packaging film packaging DETAILED DESCRIPTION

[0032] The application will be described in detail below with examples. It is necessary to point out that the specific examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application. Some non-essential improvements and adjustments made by the skilled in the art according to the content of the application above should all belong to the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

[0033] I. Preparation of carbon quantum dots

[0034] 2.101 g of citric acid and 1.752 g of citrulline were dispersed in 20 ml of deionized water by stirring, then transferred to a 50 ml high-pressure reaction tube, heated to 200℃ for 12 h, and then the product was filtered through a 0.22 μm filter membrane after cooling. Then, it was dialyzed in water for 48 h, and then freeze-dried to collect the powder for use.

[0035] II. Preparation of food fresh-keeping liquid

[0036] 1. Preparation of carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid (experimental group): A measured amount of chitosan quaternary ammonium salt was added to a measured amount of deionized water and stirred at 50℃ for 2 h to prepare a chitosan quaternary ammonium salt solution. At the same time, a measured amount of gelatin was added to a measured amount of deionized water and stirred at 50℃ for 2 h to prepare a gelatin solution. The chitosan solution and the gelatin solution were mixed, and a measured amount of carbon quantum dots (CDs) was added, then stirred at room temperature for 1 h, and then ultrasonicated for 20 min to obtain a uniform fresh-keeping liquid. The prepared fresh-keeping liquid was tested for its fresh-keeping performance on lychees.

[0037] The specific embodiment formula of the carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid is shown in Table 1:

[0038] Table 1

[0039]

[0040]

[0041] 2. Preparation of chitosan quaternary ammonium salt and gelatin food fresh-keeping liquid (control group): A measured amount of chitosan quaternary ammonium salt was added to a measured amount of deionized water and stirred at 50℃ for 2 h to prepare a chitosan quaternary ammonium salt solution. At the same time, a measured amount of gelatin was added to a measured amount of deionized water and stirred at 50℃ for 2 h to prepare a gelatin solution. The chitosan solution and the gelatin solution were mixed, and a measured amount of citric acid or citrulline was added, then stirred at room temperature for 1 h, and then ultrasonicated for 20 min to obtain a uniform fresh-keeping liquid. The prepared fresh-keeping liquid was tested for its fresh-keeping performance on lychees.

[0042] The formula of the chitosan quaternary ammonium salt and gelatin food preservation liquid is shown in Table 2:

[0043] Table 2

[0044]

[0045] III. Preparation of food packaging film

[0046] 1. Preparation of carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food packaging film (experimental group): A measured amount of chitosan quaternary ammonium salt was added to a measured amount of deionized water and stirred at 50°C for 2h to prepare a chitosan quaternary ammonium salt solution. At the same time, a measured amount of gelatin was added to a measured amount of deionized water and stirred at 50°C for 2h to prepare a gelatin solution. The chitosan quaternary ammonium salt solution and the gelatin solution were mixed, a measured amount of carbon quantum dots (CDs) was added, and then stirred at room temperature for 1h and ultrasonicated for 20min to obtain a uniform preservation liquid. A measured amount of glycerol was added to the preservation liquid, and then stirred at room temperature for 1h and ultrasonicated for 20min to obtain a uniform film-forming solution. 30ml of the film-forming solution was poured into a plastic petri dish with a diameter of 120mm, the petri dish was placed in a 35°C oven for drying, and then placed in a 20°C, 50% RH constant temperature and humidity box for 3 days of equilibrium to prepare a food packaging film. The prepared film was tested for appearance, ultraviolet resistance, antioxidant properties, antibacterial properties, and preservation performance on cherry tomatoes, etc.

[0047] The formula of the carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food packaging film is shown in Table 3:

[0048] Table 3

[0049]

[0050]

[0051] 2. Preparation of chitosan quaternary ammonium salt and gelatin food packaging film (control group): A measured amount of chitosan quaternary ammonium salt was added to a measured amount of deionized water and stirred at 50°C for 2h to prepare a chitosan quaternary ammonium salt solution. At the same time, a measured amount of gelatin was added to a measured amount of deionized water and stirred at 50°C for 2h to prepare a gelatin solution. The chitosan quaternary ammonium salt solution and the gelatin solution were mixed, a measured amount of citric acid or citrulline was added, and then stirred at room temperature for 1h and ultrasonicated for 20min to obtain a uniform preservation liquid. A measured amount of glycerol was added to the preservation liquid, and then stirred at room temperature for 1h and ultrasonicated for 20min to obtain a uniform film-forming solution. 30ml of the film-forming solution was poured into a plastic petri dish with a diameter of 120mm, the petri dish was placed in a 35°C oven for drying, and then placed in a 20°C, 50% RH constant temperature and humidity box for 3 days of equilibrium to prepare a food packaging film. The prepared film was tested for appearance, ultraviolet resistance, antioxidant properties, antibacterial properties, and preservation performance on cherry tomatoes, etc.

[0052] The formula of the chitosan quaternary ammonium salt and gelatin food preservation liquid is shown in Table 4:

[0053] Table 4

[0054]

[0055] Four, appearance test of food packaging film, ultraviolet resistance, antioxidant, antibacterial property, preservation performance test of cherry tomato and preservation performance test of food preservation liquid on litchi

[0056] 1. Appearance test of food packaging film

[0057] Place the film on an A4 paper containing a LOGO, and use a camera to record the appearance of each sample.

[0058] 1. Ultraviolet resistance test of food packaging film

[0059] Cut the film into 3x6cm rectangular strips with scissors, then place the samples in the sample holder of the ultraviolet spectrophotometer. Use the ultraviolet spectrophotometer to measure the ultraviolet transmission spectrum of the film in the range of 200-800nm, to evaluate the shielding ability of the film to ultraviolet. And take the ultraviolet transmittance values at 450, 600nm for evaluation of the visible light transmittance performance of the film.

[0060] 2. Antioxidant test of food packaging film

[0061] Place the composite film sample in deionized water and dissolve at 35℃ for 4h, then take 0.5ml supernatant and mix with 2.5ml ethanol, DPPH solution respectively, use ultraviolet spectrophotometer to measure the absorbance, then calculate the clearance rate of the film to DPPH free radical by formula:

[0062] DPPH free radical clearance rate = [1-(A i -A j ) / A0]x100%

[0063] Where A i represents the absorbance of the supernatant of the sample film solution and the DPPH ethanol solution, A j represents the absorbance of 0.5ml sample film solution supernatant and 2.5ml ethanol, A0 represents the absorbance of 0.5ml ethanol and 2.5ml DPPH ethanol solution.

[0064] 3. Antibacterial performance test of food packaging film

[0065] Take 15 mg of film and 1 ml of bacterial solution into 100 ml of physiological saline, shake in a shaking bed at 37°C, 150 rpm for 3h, then dilute the incubated liquid to a certain multiple and spread on the plate, cultivate for 24h, then count the growth of bacterial colonies, the blank control group without any film, calculate the inhibition rate by formula, formula:

[0066] Inhibition rate = (A0-A1) / A0x100%

[0067] Where A0 represents the number of colonies of the blank control group, and A1 represents the number of colonies of the sample film group.

[0068] 4. Food preservation liquid on litchi preservation performance test

[0069] Fresh litchi was soaked in a beaker containing food preservation liquid for 30s, then taken out and placed in a 9mm culture dish, and litchi without any food preservation liquid was used as a blank group. Then stored at 25°C, 80% RH, and the camera recorded the deterioration process of cherry tomato, and when the litchi skin color appeared discoloration and the flesh was not fresh, the litchi was considered to be rotten.

[0070] 5. Food packaging film on cherry tomato preservation performance test

[0071] Fresh cherry tomato was placed in a 9mm culture dish, and the composite film was covered on the culture dish to seal, and the cherry tomato without any composite film was used as a blank group. Then stored at 25°C, 80% RH, and the camera recorded the deterioration process of cherry tomato, and when the cherry tomato skin appeared wrinkles, the cherry tomato was considered to be rotten.

[0072] Four, results

[0073] The food preservation liquid of the example group on the preservation performance test of litchi is shown in Table 5:

[0074] Table 5

[0075] Examples Freshness time (d) 1 3 2 3 3 4 4 5

[0076] The food preservation liquid of the control group on the preservation performance test of litchi is shown in Table 6:

[0077] Table 6

[0078] Control group Freshness time (d) 1 2 2 2 3 2

[0079] The food packaging film of the example group on the preservation performance test of cherry tomato is shown in Table 7:

[0080] Table 7

[0081]

[0082] The anti-ultraviolet, antioxidant, antibacterial properties of the control group food packaging film and the preservation performance of cherry tomatoes were tested, as shown in Table 8:

[0083] Table 8

[0084]

[0085]

[0086] As can be seen from Tables 5 and 6, the higher the concentration of carbon quantum dots in the food preservative solution, the more significant the preservation effect on fruits. The litchi preserved by the high-concentration quantum dot example is fresher than that by other low-concentration examples and the control groups 1-3, indicating that the high-concentration example can effectively prolong the shelf life of litchi and is suitable for litchi preservation.

[0087] As can be seen from Tables 7 and 8, compared with the control group, the composite film in the example is more excellent in terms of ultraviolet barrier, antioxidant and antibacterial properties, and has a longer preservation time for cherry tomatoes. At the same time, as the content of carbon quantum dots in the example increases, the ultraviolet barrier, antioxidant and antibacterial abilities of the film are significantly enhanced, and the preservation time for cherry tomatoes is also correspondingly prolonged. The specific performance is as follows:

[0088] 1) As the concentration of carbon quantum dots increases, the ultraviolet transmittance significantly decreases, and the barrier rate of the final composite film in the 200-400 nm ultraviolet range exceeds 85%;

[0089] 2) As the concentration of carbon quantum dots increases, the DPPH clearance rate of the film significantly improves, and finally reaches 47.8%, showing excellent antioxidant properties;

[0090] 3) The antibacterial rates of the composite film on E. coli and S. aureus are 79.7% and 94.6% respectively, showing strong antibacterial properties;

[0091] 4) The preservation time of the composite film for cherry tomatoes can reach 8 days, and the preservation effect is outstanding.

[0092] Appendix Figures 1-5 The appearance pictures, ultraviolet barrier performance chart, antioxidant performance chart, litchi preservation effect picture and cherry tomato preservation effect picture of some examples and the control group are shown.

[0093] In summary, according to the results of Tables 5, 6, 7, 8 and the results of the appendix Figures 1-5 It can be seen that the carbon quantum dots prepared by the present application have excellent antioxidant and ultraviolet absorption properties; the food preservative solution and food packaging film prepared by the present application exhibit excellent antibacterial, antioxidant and ultraviolet barrier properties. When the food packaging film is applied to cherry tomato preservation and the food preservative solution is applied to litchi preservation, the preservation time of fruits can be significantly prolonged.

Claims

1. A carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food preservative liquid, food packaging film, characterized in that, The food fresh-keeping liquid comprises, in parts by weight: Chitosan quaternary ammonium salt: 0.1-1.5 parts; Gelatin: 0.1-1.5 parts; Carbon quantum dots: 0.01-0.2 parts; Deionized water: 97-99 parts; The carbon quantum dots are prepared by a hydrothermal method from edible natural raw materials, and have good biocompatibility and safety; The food packaging film comprises: The above food fresh-keeping liquid: 98-100 parts; Glycerol: 0-2 parts.

2. The carbon quantum dots enhanced antibacterial and antioxidant multifunctional active food preservative liquid, food packaging film according to claim 1, characterized in that, The carbon quantum dots not only have excellent antioxidant properties themselves, but also can significantly improve the antibacterial, antioxidant and ultraviolet blocking properties of the food fresh-keeping liquid and packaging film made of chitosan quaternary ammonium salt and gelatin.

3. A method for preparing carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid and food packaging film, characterized in that, The method comprises the following steps: S1: preparing a chitosan quaternary ammonium salt solution; S2: preparing a gelatin solution; S3: preparing carbon quantum dots; S4: mixing the chitosan quaternary ammonium salt solution, the gelatin solution and the carbon quantum dots to prepare a food fresh-keeping liquid; S5: adding glycerol to the food fresh-keeping liquid to prepare a multifunctional active food packaging film.

4. The method for preparing a carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid and food packaging film according to claim 3, characterized in that, The preparation method of the chitosan quaternary ammonium salt solution is as follows: chitosan quaternary ammonium salt is dissolved in deionized water, stirred at 50°C for 2h, and a chitosan quaternary ammonium salt solution is prepared.

5. The method for preparing a carbon quantum dot enhanced antibacterial and antioxidant multifunctional active food preservative liquid and food packaging film according to claim 3, characterized in that, The preparation method of the gelatin solution is as follows: gelatin is dissolved in deionized water, stirred at 50°C for 2h, and a gelatin solution is prepared.

6. The method for preparing a carbon quantum dots enhanced antibacterial and antioxidant multifunctional active food preservative liquid and food packaging film according to claim 3, characterized in that, The preparation method of the carbon quantum dots is as follows: citric acid and citrulline are uniformly dispersed in deionized water, then transferred to a high-pressure reaction tube, and reacted under stirring and temperature control, then the product is filtered through a 0.22μm filter membrane, then dialyzed in deionized water for 48h, and then freeze-dried for standby.

7. Use of the carbon quantum dot-enhanced antibacterial and antioxidant multifunctional active food fresh-keeping liquid and food packaging film according to any one of claims 1-6 in fruit and vegetable preservation.

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