Preparation method of quercetin-loaded polylactic acid / chitosan composite packaging film

Abstract

The invention discloses a quercetin-loaded polylactic acid / chitosan composite packaging film as well as a preparation method and application thereof, and the method comprises the following steps: dissolving chitosan in a formic acid solution to prepare a chitosan solution; polylactic acid is dissolved in a chloroform solution and then dropwise added into the DMF solution, and a polylactic acid solution is prepared; adding a chitosan solution into the polylactic acid solution to obtain a polylactic acid / chitosan mixed solution; drying the polylactic acid / chitosan mixed solution in a container to form a thin film, and pouring absolute ethyl alcohol on the thin film to enable the thin film to fall off, so as to obtain a polylactic acid / chitosan thin film; the method comprises the following steps: dissolving quercetin in absolute ethyl alcohol to obtain a quercetin solution; and dipping the polylactic acid / chitosan film in the quercetin solution to obtain the polylactic acid / chitosan / quercetin film. The composite packaging film has better mechanical strength, biodegradability, antibacterial activity and antioxidant activity, and is beneficial to prolonging the shelf life of fresh keeping of fish meat.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film. Background Art

[0002] Food packaging materials play a vital role in food preservation. Commonly used packaging materials such as polyethylene (PE) and polypropylene (PP) are mostly made of fossil-derived polymers and additives. These plastics are difficult to degrade in the environment, and potential carcinogens such as bisphenol A can diffuse from the polymers into water and the environment, posing a serious threat to human health and the environment. Therefore, the use of biodegradable polymers is of great significance. Polylactic acid (PLA) is a thermoplastic polymer extracted from renewable resources that is compostable and biocompatible. At the same time, PLA has excellent optical transparency and moderate physical toughness, and its cost is relatively low. Therefore, PLA can be used as a substitute for some traditional petroleum-based plastics and is widely used in packaging materials and biomedical fields. However, existing PLA-based bioplastics cannot meet the needs of active packaging (antioxidant, antibacterial).

[0003] Therefore, it is necessary to develop a fresh-keeping packaging material with good mechanical strength, biodegradability, antibacterial and antioxidant activities, which can help to prolong the shelf life of fish. Summary of the invention

[0004] The present invention aims to provide a quercetin-loaded polylactic acid / chitosan composite packaging film and a preparation method and application thereof. The quercetin-loaded polylactic acid / chitosan composite packaging film has good mechanical strength, biodegradability, antibacterial and antioxidant activities, and is helpful to prolong the shelf life of fish preservation.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect of the present invention, a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film is provided, the method comprising: dissolving chitosan in a formic acid solution to prepare a chitosan solution; The polylactic acid is dissolved in a chloroform solution, and then added dropwise to a DMF solution to prepare a polylactic acid solution; adding chitosan solution to the polylactic acid solution to obtain a polylactic acid / chitosan mixed solution; The polylactic acid / chitosan mixed solution is dried in a container to form a film, and then anhydrous ethanol is poured on the film to make the film fall off, thereby obtaining a polylactic acid / chitosan film; dissolving quercetin in anhydrous ethanol to obtain a quercetin solution; The polylactic acid / chitosan film is immersed in the quercetin solution to obtain a polylactic acid / chitosan / quercetin film.

[0006] Furthermore, the concentration of the polylactic acid solution is 9 g / L-11 g / L.

[0007] Furthermore, the concentration of the chitosan solution is 4 g / L-6 g / L.

[0008] Furthermore, the volume ratio of the polylactic acid solution to the chitosan solution is (5-7):(3-5), preferably 6:(3-5).

[0009] Furthermore, the concentration of the quercetin solution is 200 mg / L-800 mg / L.

[0010] Furthermore, the speed of adding the chitosan solution to the polylactic acid solution is 0.13 mL / min-0.16 mL / min.

[0011] Furthermore, the drying temperature is 55°C-65°C.

[0012] Furthermore, the immersion time is 20 h-30 h.

[0013] In a second aspect of the present invention, a quercetin-loaded polylactic acid / chitosan composite packaging film prepared by the method is provided.

[0014] In the third aspect of the present invention, there is provided the use of the quercetin-loaded polylactic acid / chitosan composite packaging film in the preparation of food preservation packaging materials.

[0015] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, wherein polylactic acid and chitosan are blended to improve mechanical strength and thermal stability. In order to further optimize the antibacterial and antioxidant properties of the composite film, the phenolic compound quercetin is mixed therewith to form an active composite film, which not only gives the food packaging material multifunctionality, but also helps to extend the shelf life of the food. In addition, the present application finds that the quercetin-loaded polylactic acid / chitosan composite packaging film prepared by combining quercetin, polylactic acid and chitosan has a synergistic and unexpected effect, improves the fresh-keeping performance, and extends the shelf life of fish. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 The results of testing the mechanical properties of the composite films of Examples 1 to 3 using a universal mechanical testing machine; Figure 2 The antioxidant test results of Experimental Example 3; Figure 3 This is the infrared characterization result; Figure 4 The antibacterial test results of Experimental Example 4; (a) blank control, (b) antibacterial results of the polylactic acid / chitosan film in Comparative Example 2 and (c) polylactic acid / chitosan / quercetin film in Example 1; Figure 5 The results of the fish preservation test of Experimental Example 5. Photos of the changes in fish meat during the sealed storage process of (a) the polyethylene film of Comparative Example 1, (b) the polylactic acid / chitosan film of Comparative Example 2, and (c) the polylactic acid / chitosan / quercetin film of Example 1; Figure 6 The results show the changes in fish meat pH, thiobarbituric acid (TBARS) (Figure a), volatile basic nitrogen (TVB-N) (Figure b), pH (Figure c) and total colony count (Figure d). DETAILED DESCRIPTION

[0018] The present invention will be described in detail below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are used to illustrate the present invention, rather than to limit the present invention.

[0019] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0020] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or obtained by existing methods.

[0021] The technical solution of the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows: According to a typical embodiment of the present invention, a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film is provided, the method comprising: S1, dissolving chitosan in a formic acid solution to prepare a chitosan solution; In the step S1, The concentration of the chitosan solution is 4 g / L-6 g / L. If the concentration is too high, the viscosity will increase, which is not conducive to extrusion; if it is too low, it will have an adverse effect of reducing the composite efficiency and the toughness of the composite film; S2, dissolving polylactic acid in a chloroform solution, and then adding dropwise to a DMF solution to prepare a polylactic acid solution; In step S2, chitosan may also be dissolved with acetic acid, and chloroform may also be dichloromethane.

[0022] The concentration of the polylactic acid solution is 9 g / L-11 g / L. If the concentration is too high, the composite film may be too brittle, and if it is too low, the composite film may have poor mechanical strength. S3, adding chitosan solution to the polylactic acid solution to obtain a polylactic acid / chitosan mixed solution; In the step S3, The volume ratio of the polylactic acid solution to the chitosan solution is (5-7): (3-5); if the volume ratio is too large, the brittleness of the composite film will increase, and if it is too small, the interface compatibility of the composite film will deteriorate. The speed of adding the chitosan solution to the polylactic acid solution is 0.13 mL / min-0.16 mL / min. Specifically, a syringe pump can be used for adding. If the adding speed is too high, the solution will be mixed unevenly and chitosan will precipitate. If it is too low, the heating time will be too long and the solvent will evaporate. S4, drying the polylactic acid / chitosan mixed solution in a container to form a film, and then pouring anhydrous ethanol on the film to make the film fall off, thereby obtaining a polylactic acid / chitosan film; In the step S4, The drying temperature is 55°C-65°C.

[0023] The immersion time is 20 h-30 h.

[0024] The preparation method of a quercetin-loaded polylactic acid / chitosan composite packaging film of the present application will be described in detail below in combination with examples, comparative examples and experimental data.

[0025] Example 1 The embodiment of the present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, comprising the following steps: 1. Experimental reagents Chitosan (200-600 mPa.s) was purchased from Tokyo Chemical Industry Co., Ltd. (TCI, Shanghai). Quercetin was purchased from Sigma-Aldrich. Polylactic acid (PLA) was purchased from Nature Works 2003D.

[0026] 2. Preparation of polylactic acid / chitosan / quercetin composite packaging film (1) Dissolve chitosan in formic acid solution to prepare a 5 g / L chitosan solution, and then stir with a magnetic stirrer until the chitosan is completely dissolved.

[0027] (2) Dissolve polylactic acid in chloroform solution and stir until polylactic acid is completely dissolved. Then, add the solution dropwise to an equal volume of DMF solution to prepare a 10 g / L polylactic acid solution. After mixing evenly, add 2% by volume of Span 80.

[0028] (3) The PLA solution was stirred at 60 °C and 1000 rpm, and then the chitosan solution was added to the PLA solution at a rate of 0.145 mL / min using a syringe pump to prepare a PLA / chitosan mixed solution with a volume ratio of 6:3.

[0029] (4) Pour the mixed solution into a petri dish and dry it in an oven at 60 °C. Then, pour anhydrous ethanol on the film to make the film fall off completely, forming a polylactic acid / chitosan film.

[0030] (5) Quercetin was dissolved in anhydrous ethanol to prepare a quercetin solution with a concentration of 500 mg / L. The polylactic acid / chitosan film was immersed in the quercetin solution for 24 h to obtain a polylactic acid / chitosan / quercetin composite film.

[0031] Example 2 The embodiment of the present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, except that the volume ratio of the polylactic acid solution to the chitosan solution is changed to 6:4, and other preparation methods are the same as those in Example 1.

[0032] Example 3 The embodiment of the present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, except that the volume ratio of the polylactic acid solution to the chitosan solution is changed to 6:5, and other preparation methods are the same as those in Example 1.

[0033] Example 4 The embodiment of the present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, which is different from Example 1 in that the concentration of quercetin is 800 mg / L, and the other preparation methods are the same as Example 1.

[0034] Example 5 The embodiment of the present invention provides a method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, which is different from Example 1 in that the concentration of quercetin is 600 mg / L, and the other preparation methods are the same as Example 1.

[0035] Comparative Example 1 In this comparative example, the film was a polyethylene film.

[0036] Comparative Example 2 This comparative example is the polylactic acid / chitosan film prepared in step 4 of the embodiment.

[0037] Comparative Example 3 The difference between this comparative example and Example 1 is that the concentration of quercetin is 200 mg / L, and the other preparation methods are the same as Example 1.

[0038] Experimental Example 1: Infrared Characterization The structures and components of polylactic acid, chitosan, quercetin and the polylactic acid / chitosan / quercetin composite film prepared in Example 1 were studied by Fourier transform infrared spectrometer (FTIR).

[0039] The results are as follows Figure 3 As shown, for the polylactic acid / chitosan / quercetin film, the -1 A broad NH and OH stretch overlap region was found nearby, which was attributed to chitosan. -1 The peaks at 1454 and 1380 cm represent the stretching vibration peaks of polylactic acid C=O. -1 The peaks at 1666 cm represent the symmetric and asymmetric bending vibrations of CH. -1 The peak at corresponds to the absorption peak of C=C in the aromatic ring, indicating the successful loading of quercetin.

[0040] Experimental Example 2: Tensile Test The mechanical properties of the composite films of Examples 1 to 3 were tested using a universal mechanical testing machine at a tensile speed of 2 mm / min. The blending of polylactic acid and chitosan is beneficial to improving its mechanical properties.

[0041] The results are as follows Figure 1 As shown, when the tensile stress (TS) is 13.2 MPa, the elongation at break of pure chitosan film reaches 5%.

[0042] As the proportion of polylactic acid increases, the elongation at break of the polylactic acid / chitosan composite film gradually increases. The ratio of polylactic acid to chitosan is selected to be 6:3-5. When the ratio of polylactic acid to chitosan reaches 6:3, the elongation at break reaches a maximum value of about 55%, and the stress value that can be tolerated is about 11.3 MPa. Therefore, the ratio of polylactic acid to chitosan is preferably 6:3.

[0043] Experimental Example 3: Antioxidant Test The ABTS method was used to evaluate the effects of adding different proportions of quercetin, 0 (Comparative Example 2), 200 (Comparative Example 3), 500 (Example 1) and 800 mg / L (Example 4), on the antioxidant properties of the polylactic acid / chitosan composite film.

[0044] Table 1 Group ABTS free radical scavenging rate (%) Comparative Example 2 81.2±1.1% Comparative Example 3 87.5±0.2% Example 1 92.2±0.2% Example 4 98.4±0.3% The results are as follows Figure 2 It shows that the ABTS radical scavenging rate of the polylactic acid / chitosan composite film without quercetin is about 81.2%. As the concentration of quercetin increases, the ABTS radical scavenging rate gradually increases. The quercetin concentration is preferably 500-800 mg / L. When the quercetin concentration is 500 mg / L, the ABTS radical scavenging rate of the polylactic acid / chitosan / quercetin composite film reaches a maximum value of about 98%, and then tends to stabilize. Therefore, the quercetin concentration is preferably 500 mg / L.

[0045] Experimental Example 4: Antibacterial Test The in vitro antibacterial activity of the composite film was tested by the plate coating counting method. The test method was as follows: Escherichia coli or Staphylococcus aureus was taken into the liquid culture medium with an inoculation loop and cultured at 37 °C for 12-16 h. The polylactic acid / chitosan / quercetin film was cut into a circle with a diameter of 6 mm and sterilized under ultraviolet light on both sides for 30 min. After sterilization, the polylactic acid / chitosan / quercetin film was added to the solution diluted to 10 -3 The reaction was carried out at 37 °C and 200 rpm for 24 h. After the reaction solution was diluted to an appropriate concentration, 100 μL of the solution was spread on the plate. After incubation at 37 °C for 24 h, the total number of colonies was determined by the plate counting method.

[0046] Figure 4 The antibacterial results of (a) blank control, (b) polylactic acid / chitosan film in comparative example 2 and (c) polylactic acid / chitosan / quercetin film in example 1 show that the antibacterial rate of polylactic acid / chitosan / quercetin film against Escherichia coli reaches 87.6%, and the antibacterial rate against Staphylococcus aureus reaches 80.5%.

[0047] Experimental Example 5: Fish preservation test The head, tail and viscera of fresh crucian carp were removed, and 20 g of fish meat was weighed and placed in a test tube, which was sealed with polyethylene film, polylactic acid / chitosan film and polylactic acid / chitosan / quercetin film, respectively, and then stored in a refrigerator at 4 °C. The changes in fish pH, ​​thiobarbituric acid (TBARS), volatile basic nitrogen (TVB-N) and total bacterial count were tested every day. Figure 5 The photos are respectively showing the changes of fish meat during the sealed storage of (a) polyethylene film of comparative example 1, (b) polylactic acid / chitosan film of comparative example 2 and (c) polylactic acid / chitosan / quercetin film of example 1.

[0048] TBRAS is an important parameter for evaluating the oxidation process of fish fat. During storage, fish fat is broken down into aldehydes, ketones and other substances, resulting in deterioration of fish quality.

[0049] Figure 6 a shows that the TBARS values ​​of samples treated with polylactic acid / chitosan / quercetin film were always lower than those of the control group, which may be due to the release of quercetin during the treatment process, which inhibited the oxidation of unsaturated fatty acids in grass carp meat.

[0050] Figure 6 b shows that there was no difference in the initial TVB-N content of all samples. As time went on, the TVB-N content of the three groups of samples gradually increased. On the 6th day, the TVB-N content of the sample treated with PE film reached 40.58 mg N / 100g, which was higher than the acceptable maximum TVB-N limit (35 mg N / 100g). On the 8th day, the TVB-N content of the samples treated with polylactic acid / chitosan and polylactic acid / chitosan / quercetin films reached 38.47 and 35.45 mg N / 100g, respectively, indicating that the fish meat was spoiled.

[0051] Figure 6 c shows that the pH changes of the three groups of samples within 9 days generally showed a trend of first decreasing and then increasing. On days 6-8, the pH of the samples treated with polylactic acid / chitosan / quercetin film was lower than that of the samples treated with polylactic acid / chitosan film, which may be due to the fact that quercetin inhibited the degradation of amino acids and the formation of biogenic amines.

[0052] Figure 6 d shows the change in total colony count. The TVC value of the sample treated with polyethylene film reached 7.1 log CFU / g on the 3rd day, exceeding the maximum limit (7 log CFU / g). On the 5th day, the TVC values ​​of the samples treated with polylactic acid / chitosan and polylactic acid / chitosan / quercetin films were 7.23 and 7.02 log CFU / g, respectively, both exceeding the TVC maximum limit.

[0053] The above results show that the polylactic acid / chitosan / quercetin film has the best preservation performance and can extend the shelf life of fish by two days.

[0054] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article, or apparatus.

[0055] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0056] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film, characterized in that: The method comprises: dissolving chitosan in a formic acid solution to prepare a chitosan solution; The polylactic acid is dissolved in a chloroform solution, and then added dropwise to a DMF solution to prepare a polylactic acid solution; adding chitosan solution to the polylactic acid solution to obtain a polylactic acid / chitosan mixed solution; The polylactic acid / chitosan mixed solution is dried in a container to form a film, and then anhydrous ethanol is poured on the film to make the film fall off, thereby obtaining a polylactic acid / chitosan film; dissolving quercetin in anhydrous ethanol to obtain a quercetin solution; The polylactic acid / chitosan film is immersed in the quercetin solution to obtain a polylactic acid / chitosan / quercetin film.

2. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The concentration of the polylactic acid solution is 9 g / L-11 g / L.

3. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The concentration of the chitosan solution is 4 g / L-6 g / L.

4. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The volume ratio of the polylactic acid solution to the chitosan solution is (5-7): (3-5).

5. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The concentration of the quercetin solution is 200 mg / L-800 mg / L.

6. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The speed of adding the chitosan solution to the polylactic acid solution is 0.13 mL / min-0.16 mL / min.

7. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The drying temperature is 55°C-65°C.

8. The method for preparing a quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 1, characterized in that: The immersion time is 20 h-30 h.

9. The quercetin-loaded polylactic acid / chitosan composite packaging film prepared according to the method according to any one of claims 1 to 8.

10. Use of the quercetin-loaded polylactic acid / chitosan composite packaging film according to claim 9 in preparing food preservation packaging materials.

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