Method for producing antibacterial preservative film by using waste polylactic acid and waste pomelo peel as raw materials

Abstract

The invention discloses a method for producing an antibacterial preservative film by using waste polylactic acid and waste pomelo peel as raw materials. The method comprises the following steps: 1) extracting grapefruit essential oil from waste grapefruit peel; 2) degrading the waste polylactic acid to obtain a polylactic acid degradation liquid; and 3) mixing the chitosan solution with the polylactic acid degradation liquid, grapefruit essential oil and glycerol, and carrying out film casting and drying to obtain the preservative film. The waste pomelo peel and the waste polylactic acid are combined, so that resource recycling of agricultural waste and industrial plastic waste is realized, and environmental pollution and white pollution are effectively reduced; meanwhile, by introducing the chitosan and the grapefruit essential oil, the preservative film is endowed with excellent biocompatibility and remarkable antibacterial performance, by introducing the grapefruit essential oil, the antibacterial performance of the film material is enhanced, the preservation period of food is prolonged, meanwhile, the safety and functionality of the packaging material are improved, and the environment benefits and application prospects are remarkable.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a method for producing antibacterial preservation film using waste polylactic acid and waste grapefruit peel as raw materials. Background Technology

[0002] Grapefruit, a popular fruit, is widely cultivated and consumed globally. my country is one of the major grapefruit producers, generating a large amount of waste grapefruit peels annually. These peels are typically discarded as agricultural waste in fields or landfills, wasting resources and causing bacterial growth, unpleasant odors, and environmental pollution. However, grapefruit peels actually contain abundant bioactive components, such as flavonoids, polysaccharides, and essential oils, possessing antioxidant, antibacterial, and anti-inflammatory properties. Currently, the resource utilization rate of grapefruit peels is low, and their full value has not been realized.

[0003] Polylactic acid (PLA) is a biodegradable polymer material with good biocompatibility, processability, and mechanical properties, and is widely used in packaging, fiber, and medical fields. With the widespread use of PLA products, the amount of waste PLA is also increasing. Although PLA is a biodegradable bio-based material, its degradation cycle is relatively long, placing a significant burden on the environment. Therefore, how to achieve efficient recycling and resource utilization of waste PLA has become an urgent problem to be solved.

[0004] Therefore, using waste grapefruit peels and waste polylactic acid to produce food preservation film can not only reduce environmental pollution, but also meet the market demand for environmentally friendly food preservation film. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for producing antibacterial food preservation film using waste polylactic acid and waste grapefruit peel as raw materials, aiming to reduce white pollution and environmental pollution, and turn waste into treasure.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for producing antibacterial food preservation film using waste polylactic acid and waste grapefruit peel as raw materials includes the following steps:

[0008] (1) Extracting grapefruit essential oil from discarded grapefruit peels;

[0009] (2) Degrade the waste polylactic acid to obtain polylactic acid degradation liquid;

[0010] (3) Mix chitosan solution with polylactic acid degradation solution and grapefruit essential oil, then cast and dry to obtain a plastic wrap.

[0011] Preferably, the polylactic acid degradation solution is prepared by dissolving waste polylactic acid under high temperature with NaOH and then neutralizing it.

[0012] Preferably, the grapefruit essential oil is obtained by steam distillation of waste grapefruit peel.

[0013] Preferably, the above method further includes the step of adding a plasticizer.

[0014] Preferably, the plasticizer is glycerol.

[0015] Preferably, the above method includes the following steps: take 2.5 g of chitosan, dissolve it in 100 mL of 1% acetic acid solution at 50°C, and stir for 1 h; add 0.5 mL of glycerol and stir for 30 min; then add polylactic acid degradation solution and grapefruit essential oil, mix well to obtain film-forming solution, pour the film-forming solution into a mold, dry it, and obtain plastic wrap.

[0016] Preferably, the final concentration of the polylactic acid degradation solution in the film-forming solution is 5% (1 / 4MIC) by mass volume percentage.

[0017] Preferably, the final concentration of grapefruit essential oil in the film-forming solution is 15% by volume.

[0018] On the other hand, the present invention also provides a food preservation film prepared according to the above method.

[0019] On the other hand, the present invention also provides the application of the plastic wrap in food preservation.

[0020] This invention provides a method for producing antibacterial food preservation film using waste polylactic acid and waste grapefruit peel as raw materials. Its beneficial effects are as follows: by combining waste grapefruit peel with waste polylactic acid, not only is the resource recycling of agricultural waste and industrial plastic waste achieved, effectively reducing environmental pollution and "white pollution"; simultaneously, by introducing chitosan and grapefruit essential oil, the food preservation film is endowed with excellent biocompatibility and significant antibacterial properties. The introduction of grapefruit essential oil enhances the antibacterial properties of the film material, extends the shelf life of food, and improves the safety and functionality of packaging materials, demonstrating significant environmental benefits and application prospects. Attached Figure Description

[0021] Figure 1 Image showing the antibacterial effect of grapefruit oil-polylactic acid (PLA) plastic wrap. CK indicates bacterial growth without the film; +1 / 4MIC indicates chitosan plastic wrap containing 1 / 4MIC PLA alkaline degradation solution; +1 / 4MIC+grapefruit oil indicates chitosan plastic wrap containing 15% grapefruit oil and 1 / 4MIC PLA alkaline degradation solution. Detailed Implementation

[0022] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0023] Example 1

[0024] 1. Preparation of grapefruit essential oil

[0025] The essential oil extracted from waste grapefruit peel using the steam extraction method includes the following steps: Fresh waste grapefruit peel is washed, sliced, dried in an oven at 55℃ to constant weight, and then pulverized through a 40-mesh sieve to obtain dried grapefruit peel powder; the dried grapefruit peel powder and deionized water are added to a distillation vessel at a material-to-liquid ratio of 1 g: 10 mL, soaked for 30 min, heated to a gentle boil, and continuously distilled for 4 h, allowing the steam to carry the essential oil through a condenser. The distillate is collected, the upper oil phase is separated using a separatory funnel, anhydrous sodium sulfate is added and dried overnight, the desiccant is filtered off, and the grapefruit essential oil is obtained and stored in a sealed container at 4℃ away from light.

[0026] 2. Preparation of PLA degradation solution

[0027] Waste PLA was washed, dried, and cut into fragments ≤5 mm × 5 mm. The fragments were added to a 0.5 mol / L NaOH solution at a solid-liquid ratio of 1 g: 10 mL and stirred at 180℃ for 2 h until completely dissolved. The solution was filtered while hot to remove insoluble impurities, yielding a clear PLA alkaline hydrolysis solution. After cooling to room temperature in an ice-water bath, 1 mol / L HCl was added dropwise while stirring to adjust the pH to 6.5-7.0, thus obtaining the PLA degradation solution. The solution was sealed and stored at 4℃ for later use.

[0028] 3. Determination of the minimum inhibitory concentration (MIC) of PLA degradation solution

[0029] 10 μL of Staphylococcus aureus and Escherichia coli suspension (OD) 600 =1) Add to a 96-well plate containing PLA degradation solution of different concentrations diluted by the double-soup method, and incubate at 37°C for 24 h. The minimum inhibitory concentration (MIC) is the concentration at which no visible bacterial growth is observed.

[0030] The results showed that the minimum inhibitory concentration (MIC) of PLA degradation solution against Staphylococcus aureus and Escherichia coli was 20% (200 mg / mL).

[0031] 4. Preparation of plastic wrap

[0032] (1) Preparation of chitosan + grapefruit essential oil - polylactic acid plastic wrap

[0033] 2.5 g of chitosan was dissolved in 100 mL of 1% (w / v) acetic acid solution at 50 °C and stirred thoroughly for 1 h. Then, 0.5 mL of glycerol was added and stirred for 30 min. A certain amount of PLA degradation solution and grapefruit essential oil were added and mixed well to obtain a film-forming solution. 20 mL of the film-forming solution was poured into a film-forming mold and placed in an oven at 45 °C for 48 h to obtain a plastic wrap. The final concentration of PLA degradation solution in the film-forming solution was 1 / 4 MIC (i.e., 5% or 50 mg / mL), and the final concentration of grapefruit essential oil in the film-forming solution was 15% (v / v).

[0034] (2) Preparation of chitosan preservation film containing 1 / 4MIC PLA alkaline degradation solution

[0035] Take 2.5 g of chitosan and dissolve it in 100 mL of 1% (mass fraction) acetic acid solution at 50℃, and stir thoroughly for 1 h. Then add 0.5 mL of glycerol and stir for 30 min. Add a certain amount of PLA degradation solution and mix well to obtain the film-forming solution. Take 20 mL of the film-forming solution and pour it into a film-forming container, and place it in an oven at 45℃ for 48 h to obtain the plastic wrap. The final concentration of PLA degradation solution in the film-forming solution is 1 / 4 MIC concentration (i.e., 5% or 50 mg / mL).

[0036] 5. Biofilm antibacterial verification

[0037] The membrane was sterilized under ultraviolet light for 1 hour, and 0.8 g of the membrane was added to a solution containing 10 mL of OD. 600 In a 0.3% concentration of either *E. coli* or *Staphylococcus aureus* bacterial suspension, the bacterial solution without biological preservation film served as the control (CK). The mixture was incubated with shaking at 37°C for 4 hours, and then diluted 10⁻⁶ times. 4 Then, 50 μL was placed on an LB agar plate and incubated at 37°C for 24 h to observe the colony density.

[0038] Figure 1 The figure shows the antibacterial effect of grapefruit essential oil-polylactic acid (PLA) plastic wrap. As can be seen from the figure, the chitosan plastic wrap containing both 15% grapefruit essential oil and 1 / 4 MIC PLA alkaline degradation solution has the best antibacterial effect, which is significantly better than the chitosan plastic wrap containing only +1 / 4 MIC PLA alkaline degradation solution. This result indicates that grapefruit essential oil can significantly improve the antibacterial effect of plastic wrap.

[0039] The above detailed description is a specific description of the embodiments of the present invention. These embodiments are not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included in the patent scope of this case.

Claims

1. A method for producing an antibacterial food preservation film using waste polylactic acid and waste grapefruit peel as raw materials, characterized in that, Includes the following steps: (1) Extracting grapefruit essential oil from discarded grapefruit peels; (2) Degrade the waste polylactic acid to obtain polylactic acid degradation liquid; (3) Mix chitosan solution with polylactic acid degradation solution and grapefruit essential oil, then cast and dry to obtain a plastic wrap.

2. The method according to claim 1, characterized in that, The polylactic acid degradation solution is prepared by dissolving waste polylactic acid under high temperature with NaOH and then neutralizing it.

3. The method according to claim 1, characterized in that, The grapefruit essential oil is obtained by steam distillation of waste grapefruit peel.

4. The method according to claim 1, characterized in that, It also includes the step of adding plasticizers.

5. The method according to claim 4, characterized in that, The plasticizer is glycerol.

6. The method according to claim 5, characterized in that, The process includes the following steps: Take 2.5 g of chitosan, dissolve it in 100 mL of 1% acetic acid solution at 50℃, and stir for 1 h; add 0.5 mL of glycerol and stir for 30 min; then add polylactic acid degradation solution and grapefruit essential oil, mix well to obtain film-forming solution, pour the film-forming solution into a mold, dry it, and obtain plastic wrap.

7. The method according to claim 6, characterized in that, The final concentration of the polylactic acid degradation solution in the film-forming solution is 5% by mass / volume.

8. The method according to claim 6, characterized in that, The final concentration of grapefruit essential oil in the film-forming solution is 15% by volume.

9. The food preservation film prepared by the method according to any one of claims 1-8.

10. The application of the plastic wrap according to claim 9 in food preservation.

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