Preparation method of cold white photocatalytic active packaging film and application of cold white photocatalytic active packaging film in meat packaging

Abstract

The invention relates to a preparation method of a cold white photocatalytic activity packaging film and application of the cold white photocatalytic activity packaging film in meat packaging, and the cold white photocatalytic activity packaging film with self-activation and high sterilization capability is prepared by utilizing the photosensitive characteristic of cold white light excitation graphite phase carbon nitride nanosheets (g-CNN) and taking polylactic acid (PLA) as a carrier. The killing rate on food-borne harmful bacteria (taking escherichia coli and staphylococcus aureus as examples) is 99.99%, the shelf life of meat products (taking pork as examples) can be effectively prolonged by 2-3 times, and the method has a wide application prospect in the meat product industry.

Description

Technical Field

[0001] The present invention belongs to the field of food packaging technology, and particularly relates to a preparation method of a cold white light catalytically active packaging film and its application in meat packaging, especially the preparation method of the cold white light catalytically active packaging film and its continuously high bactericidal activity activated by light for meat preservation. Background Art

[0002] During the storage of meat, spoilage caused by microbial contamination will result in economic losses and pose a threat to human health. In recent years, photocatalytic sterilization technology, as a new type of non-thermal sterilization technology with low energy consumption, no chemical residues, and no environmental pollution, has attracted public attention. The photocatalytic technology relies on the reactive oxygen species (ROS) generated by light-exciting photosensitizers to attack microorganisms and cause microbial oxidative death, and has been widely studied in the fields of biology and medicine. In the food field, photocatalysis has excellent killing effects on foodborne harmful bacteria.

[0003] Graphitic carbon nitride nanosheets (g-CNN) is an inorganic non-metallic photosensitizer prepared from exfoliated graphitic carbon nitride (g-C3N4). It can absorb light energy under the irradiation of cold white light (420nm - 760nm), excite the electrons on its surface to form electron-hole pairs, and react with oxygen and water to generate reactive oxygen species such as hydroxyl radicals and superoxide anions. Poly(lactic acid) (PLA) is a new type of biodegradable material made from renewable plant resources and has good mechanical and physical properties.

[0004] CN115260682B mentions a preparation method of a recyclable photocatalytic fresh-keeping film: calcining and compounding urea with a titanium dioxide precursor to obtain carbon nitride / titanium dioxide nanoparticles; mixing a chitosan solution and a polyvinyl alcohol solution and stirring to obtain a blend solution, adding carbon nitride / titanium dioxide nanoparticles to the blend solution to obtain a film-forming solution, and then uniformly casting the film-forming solution into a mold and drying to obtain a carbon nitride / titanium dioxide / chitosan / polyvinyl alcohol photocatalytic fresh-keeping film. This film can be used in the fields of food, fruits, vegetables and fresh food preservation. CN115368602B discloses a preparation method of a green photocatalytic fresh-keeping film: using CuI as a bactericide and CuI / C3N4 as a photocatalytic composite material, and then dispersing CuI / C3N4 in a mixed solution of chitosan and polyvinyl alcohol to obtain a film-forming solution, and then preparing a carbon nitride-based green photocatalytic fresh-keeping film by phase inversion. The above patents have good fresh-keeping effects on food from the perspective of environmental protection. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a cold white light catalytically active packaging film and its application in meat packaging.

[0006] To achieve the above and other related objectives, the technical solution provided by the present invention is as follows: A preparation method of a cold white light catalytically active packaging film. Poly(lactic acid) is added to a solvent, and after stirring, a poly(lactic acid) solution is obtained; then, a graphite carbon nitride nanosheet photosensitizer capable of sterilizing with cold white light is added, and after stirring, a film-forming solution is formed; the film-forming solution is laid flat and dried to form a PLA / g-CNN film, which is the cold white light catalytically active packaging film.

[0007] The preferred technical solution is: The addition amount of the graphite carbon nitride nanosheet photosensitizer is 2-5% of the mass of the poly(lactic acid) solution.

[0008] The preferred technical solution is: The preparation method of the graphite carbon nitride nanosheet photosensitizer includes: adding g-C3N4 powder to an aqueous NaOH solution with a mass fraction of 20%-60% and performing ultrasonic treatment at room temperature for 1-3 hours; then centrifuging to obtain a precipitate, placing the precipitate in an aqueous NaOH solution with a mass fraction of 15-25%, and stirring at 50-70°C for 48-72 hours; finally, obtaining the g-CNN photosensitizer capable of utilizing cold white light through centrifugation and washing until neutral.

[0009] The preferred technical solution is: The preparation method of the g-C3N4 powder includes: synthesizing graphite carbon nitride by chemical vapor deposition: placing melamine in a covered ceramic crucible; placing it in a nitrogen atmosphere at 550°C for 3-5 h, taking out the corresponding yellow solid, and grinding to obtain g-C3N4 powder.

[0010] The preferred technical solution is: The solvent is chloroform, and the mass concentration of the poly(lactic acid) solution is 2-8%.

[0011] To achieve the above and other related objectives, the technical solution provided by the present invention is: The application of the cold white light catalytically active packaging film in meat packaging. The present invention uses PLA as the film-forming matrix of the photosensitizer g-CNN, meeting the requirements of the mechanical properties, physical properties, and green recyclability of the packaging film to achieve the extension of the shelf life of meat.

[0012] Due to the application of the above technical solution, the advantages of the present invention compared with the prior art are: 1. The present invention uses g-CNN and PLA as raw materials to prepare a photocatalytically active packaging film, which can improve the utilization rate of cold white light. Cold white light has been used in the sales process of meat, and it has excellent killing efficacy activated by cold white light against the invasion of foodborne harmful bacteria in the sales process of meat. The method for preparing the active packaging film of the present invention is simple to operate, low in cost, and can effectively preserve fresh pork.

[0013] 2. The present invention is simple and convenient, with a short processing time, low cost, green and pollution-free, and is easy to be directly applied to the sales environment of market meat products. It also has a certain control and prevention effect, providing strong technical support for maintaining public health. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the bactericidal ability against Escherichia coli in Experimental Example 2 of the present invention.

[0015] Figure 2 It is the bactericidal ability against Staphylococcus aureus in Experimental Example 3 of the present invention.

[0016] Figure 3 It is the influence on TVC during the sales of fresh pork in Comparative Example 4 of the present invention.

[0017] Figure 4 It is the influence on TVB-N during the sales of fresh pork in Comparative Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this embodiment.

[0019] Please refer to Figures 1-4 . It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have technical essential significance. Any modification of the structure, change of the proportional relationship or adjustment of the size. The following embodiments are provided to better understand the present invention, rather than to limit the present invention. The experimental materials used in the following embodiments are all obtained from conventional biochemical reagent stores without special instructions.

[0020] Example 1: Preparation Method of a Cold White Light Catalytic Active Packaging Film and Its Application in Meat Products The film matrix of the cold white light catalytic active packaging film uses green biodegradable polylactic acid.

[0021] A preparation method of a cold white light catalytic active packaging film includes the following steps: Step 1: Synthesize graphitic carbon nitride by chemical vapor deposition method: Put 2 g of melamine into a ceramic crucible with a lid. The ceramic crucible is placed in a nitrogen atmosphere at 550 °C for 4 h.

[0022] Step 2: Take out the corresponding yellow solid and grind it into g-C3N4 powder.

[0023] Step 3: Take out the g-C3N4 powder and prepare the g-CNN photosensitizer that can utilize cold white light sterilization from g-C3N4 by means of nano-exfoliation.

[0024] Step 3: Add 3 g of PLA into 100 mL of chloroform and stir magnetically for 48 h to form a 3% PLA solution. Then add 5% of g-CNN and stir for 2 h to form a film-forming solution.

[0025] Step 4: Place 10 mL of the film-forming solution in a glass petri dish with a diameter of 9 cm and dry it at 25°C to form a PLA / g-CNN film.

[0026] Example 2: Application of a cold white light catalytically active packaging film in self-starting killing of foodborne harmful bacteria, the active packaging film prepared by the preparation method of the cold white light catalytically active packaging film; select foodborne harmful bacteria; take 17.5 μL of the bacterial suspension and irradiate it on the PLA / g-CNN film for killing.

[0027] Preferably, the bacteria in food that can be killed include: Escherichia coli, Staphylococcus aureus; when performing irradiation, select a cold white light source and the irradiation time is 15 - 45 min.

[0028] Example 3: Application of a cold white light catalytically active packaging film in the preservation of meat products. Taking the actual sales scenario of pork as an example, wrap the fresh pork with a PLA / g-CNN film (relative humidity = 40%, temperature = 20°C). Use cold white light to irradiate the pork, measure the preservation indicators, and evaluate its preservation effect: Preferably, the food pork preservation indicators are: total viable count and total volatile basic nitrogen.

[0029] Comparative Example 1: Do not perform any treatment.

[0030] Comparative Example 2: Perform light treatment on fresh pork.

[0031] Comparative Example 3: Wrap the pork with a PLA / g-CNN active packaging film without performing light treatment.

[0032] Comparative Example 4: A single PLA film.

[0033] Comparative Example 5: Perform light treatment on the PLA film.

[0034] Experimental Example 1: Select Escherichia coli ( E. coli: ATCC 25922)As a representative bacterium of Gram-negative bacteria. According to the above method, the bacterial suspension was diluted to 1.0 × 10 7 CFU mL −1 with PBS (0.01 M, pH = 7.4). Take 17.5 μL of the bacterial suspension and drop it on a PLA / g-CNN membrane with a diameter of 10 mm, and irradiate it with cold white light for 15, 30, and 45 min respectively. Wash the residual bacteria on the membrane surface with PBS (200 μL, 0.01M, pH = 7.4). Subsequently, spread the mixed solution of PBS and the remaining bacteria on an LB plate and incubate it at 37 °C for 24 h to evaluate the self-activating bactericidal ability of the membrane. Then, comparative experiments were carried out in Comparative Example 1, Comparative Example 2, and Comparative Example 3 in the same manner as above, and the experimental results are as Figure 1 shown.

[0035] Figure 1 shown that there was no significant reduction in the number of Escherichia coli colonies in Comparative Example 3 or Comparative Example 2. However, as the irradiation time of Example 2 increased, the number of Escherichia coli gradually decreased, indicating that light could activate the PLA / g-CNN membrane to produce bactericidal activity. When the irradiation time was extended to 45 min, Escherichia coli had been completely killed, indicating that the membrane could produce excellent bactericidal performance through self-activation. To verify whether Comparative Example 4 had bactericidal activity, Comparative Example 4 was tested. The results showed that under cold white light irradiation, Comparative Example 4 had no self-activating bactericidal activity. The bactericidal performance of the membrane was derived from g-CNN, which produced ROS through the oxidation of oxygen and water under light irradiation conditions.

[0036] Experimental Example 2: Staphylococcus aureus ( S. aureus: ATCC 29213 was selected as the representative bacterium of Gram-positive bacteria. According to the above method, the bacterial suspension was diluted to 1.0 × 10 7 CFU mL −1 with PBS (0.01 M, pH = 7.4). Take 17.5 μL of the bacterial suspension and drop it on a PLA / g-CNN membrane with a diameter of 10 mm, and irradiate it with cold white light for 15, 30, and 45 min respectively. Wash the residual bacteria on the membrane surface with PBS (200 μL, 0.01 M, pH = 7.4). Subsequently, spread the mixed solution of PBS and the remaining bacteria on an LB plate and incubate it at 37 °C for 24 h to evaluate the self-activating bactericidal ability of the membrane. Then, comparative experiments were carried out in Comparative Example 1, Comparative Example 2, and Comparative Example 3 in the same manner as above, and the experimental results are as Figure 2 shown.

[0037] As Figure 2 shown, Example 2 also showed excellent bactericidal effects against Staphylococcus aureus, confirming the broad-spectrum bactericidal effect of the membrane in Example 2.

[0038] Experimental Example 3: Simulate the application scenario in the actual pork sales process, wrap the fresh pork with Example 4 (relative humidity = 40%, temperature = 20 °C). Irradiate the pork with cold white light, measure the following indicators, and evaluate its total viable count: The total number of colonies was determined according to the Chinese national standard (GB 4789.2-2016). Take 30 g of meat sample, add 40 mL of normal saline to homogenize in a sterile centrifuge tube. After continuously diluting the bacterial solution by decimal point for 100 μL, transfer it to a medium at 37 °C and incubate at a constant temperature for 48 h. The results are expressed as Log CFU / g of meat sample.

[0039] The TVC values of 5 groups of pork samples gradually increased within 7 days of storage ( Figure 3 ). Compared with the blank control group, the treatments of other groups all had a significant inhibitory effect on the growth of pork bacteria (p<0.05), and among them, Example 4 had the best antibacterial effect. According to the Chinese national standard (GB / T 9959.2-2008), the number of microorganisms detected in fresh pork should be less than 10 6 CFU / g. On the 5th day of storage, the TVC value of Comparative Example 1 reached 6.33 log CFU / g. The TVC value of Example 4 was the lowest, and the TVC value was less than 4 log CFU / g on the 7th day of storage. Therefore, it can be concluded that the PLA / g-CNN film can achieve ultra-long-lasting freshness of pork by effectively inhibiting bacteria under cold white light.

[0040] Experimental Example 4: Simulate the application scenario in the actual pork sales process, wrap the fresh pork with Example 4 (relative humidity = 40%, temperature = 20 °C). Irradiate the pork with cold white light, measure the following indicators, and evaluate its total volatile basic nitrogen: The TVB-N value was calculated according to the Chinese national standard (GB 5009.228-2016) using an automatic Kjeldahl nitrogen analyzer.

[0041] During the storage of pork, due to the action of microorganisms and enzymes, alkaline nitrogen-containing substances, namely total volatile basic nitrogen (TVB-N), will be produced. According to the Chinese national standard (GB 5009.228-2016), when the TVB-N content of fresh pork exceeds 15 mg / 100g, it is considered spoiled. As Figure 3 shown, during the storage period of 0-7 d, the production rate of TVB-N in Comparative Example 1 was significantly higher than that of other groups. The TVB-N produced by the pork samples treated with Example 4 on the 3rd day was significantly lower than that of other treatment groups (p<0.05), and the TVB-N was less than 15 mg / 100g on the 7th day. The experimental results show that the combination of the composite film and cold white light can significantly delay the spoilage process of pork.

[0042] Example 4: Preparation Method of a Cold White Light Catalytically Active Packaging Film and Its Application in Meat Packaging A preparation method of a cold white light catalytically active packaging film, comprising adding polylactic acid into a solvent, stirring to obtain a polylactic acid solution; then adding a graphite phase carbon nitride nanosheet photosensitizer capable of sterilizing by cold white light, and stirring to form a film-forming solution; spreading the film-forming solution, and drying to form a PLA / g-CNN film, which is the cold white light catalytically active packaging film.

[0043] The preferred embodiment is that the addition amount of the graphite phase carbon nitride nanosheet photosensitizer is 2% of the mass of the polylactic acid solution.

[0044] The preferred embodiment is that the preparation method of the graphite phase carbon nitride nanosheet photosensitizer comprises: adding g-C3N4 powder into an aqueous NaOH solution with a mass fraction of 20% and performing ultrasonic treatment at room temperature for 1 hour; then centrifuging to obtain a precipitate, placing the precipitate in an aqueous NaOH solution with a mass fraction of 15%, and stirring at 50 °C for 48 hours; finally, obtaining the g-CNN photosensitizer capable of using cold white light through centrifugation and washing until neutral.

[0045] The preferred embodiment is that the preparation method of the g-C3N4 powder comprises: synthesizing graphite phase carbon nitride by chemical vapor deposition: putting melamine into a covered ceramic crucible; placing it in a nitrogen atmosphere at 550 °C for 3 h, taking out the corresponding yellow solid, and grinding to obtain g-C3N4 powder.

[0046] The preferred embodiment is that the solvent is chloroform, and the mass concentration of the polylactic acid solution is 2%.

[0047] Application of the cold white light catalytically active packaging film in meat packaging. In the present invention, PLA is used as the film-forming matrix of the photosensitizer g-CNN, meeting the requirements of the mechanical properties, physical properties and green recyclability of the packaging film to achieve the extension of the shelf life of meat.

[0048] Example 5: Preparation Method of a Cold White Light Catalytically Active Packaging Film and Its Application in Meat Packaging A preparation method of a cold white light catalytically active packaging film, comprising adding polylactic acid into a solvent, stirring to obtain a polylactic acid solution; then adding a graphite phase carbon nitride nanosheet photosensitizer capable of sterilizing by cold white light, and stirring to form a film-forming solution; spreading the film-forming solution, and drying to form a PLA / g-CNN film, which is the cold white light catalytically active packaging film.

[0049] The preferred embodiment is that the addition amount of the graphite phase carbon nitride nanosheet photosensitizer is 5% of the mass of the polylactic acid solution.

[0050] The preferred embodiment is that the preparation method of the graphitic carbon nitride nanosheet photosensitizer includes: adding g-C3N4 powder into an aqueous NaOH solution with a mass fraction of 60% and performing ultrasonic treatment at room temperature for 3 hours; then centrifuging to obtain a precipitate, placing the precipitate in an aqueous NaOH solution with a mass fraction of 25%, and stirring at 70 °C for 72 hours; finally, obtaining the g-CNN photosensitizer that can utilize cold white light through centrifugation and washing until neutral.

[0051] The preferred embodiment is that the preparation method of the g-C3N4 powder includes: synthesizing graphitic carbon nitride by chemical vapor deposition: putting melamine into a covered ceramic crucible; placing it in a nitrogen atmosphere at 550 °C for 5 h, taking out the corresponding yellow solid, and grinding to obtain the g-C3N4 powder.

[0052] The preferred embodiment is that the solvent is chloroform and the mass concentration of the polylactic acid solution is 8%.

[0053] The above are only preferred embodiments for explaining the present invention and are not intended to limit the present invention in any form. Therefore, any modifications or changes to the present invention made under the same inventive spirit should still be included in the scope intended to be protected by the present invention.

Claims

1. A preparation method of a cold white light catalytically active packaging film, characterized in that: Add polylactic acid into a solvent, and stir to obtain a polylactic acid solution; then add a graphite-phase carbon nitride nanosheet photosensitizer that can sterilize with cold white light, and stir to form a film-forming solution; spread the film-forming solution flat and dry to form a PLA / g-CNN film, which is a cold white light catalytically active packaging film.

2. The preparation method of the cold white light-catalyzed active packaging film according to claim 1, characterized in that: The addition amount of the graphite-phase carbon nitride nanosheet photosensitizer is 2-5% of the mass of the polylactic acid solution.

3. The preparation method of the cold white light catalytic active packaging film according to claim 1, wherein: The preparation method of the graphite-phase carbon nitride nanosheet photosensitizer includes: adding g-C3N4 powder into an aqueous NaOH solution with a mass fraction of 20%-60% and ultrasonically treating it at room temperature for 1-3 hours; then centrifuging to obtain a precipitate, placing the precipitate in an aqueous NaOH solution with a mass fraction of 15-25%, and stirring at 50-70°C for 48-72 hours; finally, obtaining a g-CNN photosensitizer that can utilize cold white light through centrifugation and washing until neutral.

4. The preparation method of the cold white light catalytic active packaging film according to claim 1, characterized in that: The preparation method of g-C3N4 powder includes: synthesizing graphite-phase carbon nitride by chemical vapor deposition: putting melamine into a covered ceramic crucible; placing it in a nitrogen atmosphere at 550°C for 3-5 h, taking out the corresponding yellow solid, and grinding to obtain g-C3N4 powder.

5. The preparation method of the cold white light catalytic active packaging film according to claim 1, wherein: The solvent is chloroform, and the mass concentration of the polylactic acid solution is 2-8%.

6. Application of the cold white light catalytically active packaging film according to any one of claims 1-5 in meat packaging.

Images