Composite film, preparation method and application

Abstract

The invention provides a composite film, a preparation method and application. Specifically, the composite film is prepared from 30 to 70 parts of pectin, 400 to 500 parts of chitosan quaternary ammonium salt, 0.03 to 0.7 part of riboflavin, 300 to 400 parts of glycerol and 100 to 200 parts of water. The pectin, the chitosan quaternary ammonium salt, the riboflavin and the glycerol form the composite film, so that the composite film has excellent moisture absorption, antifogging and antibacterial effects, the possibility of moisture condensation caused by respiration of fruits and vegetables can be reduced under the condition of avoiding water loss and wilting of the fruits and vegetables, and meanwhile, the growth of microorganisms is inhibited, so that the shelf life of the fruits and vegetables is prolonged.

Description

Technical Field

[0001] The present disclosure relates to the technical field of food packaging materials, and in particular to a composite film, a preparation method and an application thereof. Background Art

[0002] my country is one of the origins of rapeseed, which can be traced back to the Illustrated Book of Materia Medica, which records that rapeseed is similar to Chinese cabbage, has tiny thorns on its leaves, and can be eaten as a vegetable. With the advancement of science and technology, relevant studies have confirmed that rapeseed is rich in nutrients such as vitamins, minerals, and dietary fiber, which can not only improve immunity, but also prevent diseases such as cancer. However, due to the large surface area of ​​rapeseed leaves, high water content, and tender leaf tissue, mechanical damage, leaf shrinkage, yellowing, and rotting are prone to occur during post-harvest storage, which not only increases the storage and transportation costs of rapeseed, but also reduces the shelf life of rapeseed, affecting the scale and scope of rapeseed production and operation. Summary of the invention

[0003] In view of this, the purpose of the present disclosure is to provide a composite film, a preparation method and an application.

[0004] Based on the above purpose, the present disclosure provides a composite film, which includes 30-70 parts of pectin, 400-500 parts of chitosan quaternary ammonium salt, 0.03-0.7 parts of riboflavin, 300-400 parts of glycerol and 100-200 parts of water.

[0005] In some embodiments, the water contact angle of the composite film is no more than 67°.

[0006] In some embodiments, the composite film includes 50-60 parts of pectin, 430-460 parts of chitosan quaternary ammonium salt, 0.1-0.2 parts of riboflavin, 330-360 parts of glycerol and 120-170 parts of water.

[0007] Based on the same inventive concept, the present disclosure also provides a method for preparing a composite film, comprising:

[0008] S1: dissolving chitosan quaternary ammonium salt, pectin and riboflavin in water respectively to obtain chitosan quaternary ammonium salt solution, pectin solution and riboflavin solution;

[0009] S2: at a preset temperature, adding pectin solution, riboflavin solution and glycerol to the chitosan quaternary ammonium salt solution in sequence, and mixing in the dark to obtain a mixed solution;

[0010] S3: Casting and drying the mixed solution after removing bubbles to obtain the composite film.

[0011] In some embodiments, the mass concentration of chitosan quaternary ammonium salt in the chitosan quaternary ammonium salt solution is 0.015 g / mL to 0.025 g / mL; and / or

[0012] The mass concentration of pectin in the pectin solution is 0.005 g / mL to 0.015 g / mL; wherein the temperature of the water dissolving the pectin is 45° C. to 55° C.; and / or;

[0013] The mass concentration of riboflavin in the riboflavin solution is 0.1-0.2 mg / mL, wherein the temperature of the water dissolving the riboflavin is 50° C.-60° C.

[0014] In some embodiments, the preset temperature is 45°C to 55°C.

[0015] In some embodiments, the water content of the composite film is not higher than 20%.

[0016] In some embodiments, the volume ratio of the chitosan quaternary ammonium salt solution to the pectin solution in step S2 is 1:0.11 to 1:0.66; and / or

[0017] The volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the glycerol is 1:0.005 to 1:0.02; and / or

[0018] The volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the volume of the riboflavin solution is 1:0.001 to 1:0.20.

[0019] In some embodiments, step S2 is mixed by magnetic stirring; wherein the magnetic stirring time is 20 min to 40 min, and the rotation speed is 200 rpm / min to 500 rpm / min.

[0020] In some embodiments, in step S3, the bubbles are removed by ultrasound; wherein the power of the ultrasound is 200W to 500W, and the time is 10min to 30min; and / or

[0021] The drying temperature is 20° C. to 60° C., and the drying time is 10 h to 30 h.

[0022] In some embodiments, the cast support is an acrylic plate.

[0023] Based on the same inventive concept, the embodiments of the present disclosure also provide the use of the composite film obtained by any of the above-mentioned composite films or any of the preparation methods in food packaging.

[0024] From the above description, it can be seen that the composite film, preparation method and application provided by the embodiments of the present disclosure form a composite film through pectin, chitosan quaternary ammonium salt, riboflavin and glycerol, so that the composite film has excellent moisture absorption, anti-fog and antibacterial effects, can reduce the possibility of water condensation generated by the respiration of fruits and vegetables while avoiding water loss and wilting of fruits and vegetables, and inhibit the growth of microorganisms, thereby extending the shelf life of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the present disclosure or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 Showing the actual photographs of the composite films obtained in Examples 1 to 5 of the present disclosure and Comparative Example 1;

[0027] Figure 2 The mechanical properties of the composite films obtained in Examples 1 to 5 and Comparative Example 1 of the present disclosure are shown;

[0028] Figure 3 The thermal stability performance result graphs of the composite films obtained in Examples 1 to 5 and Comparative Example 1 of the present disclosure are shown; wherein (a) represents the thermogravimetric curve, and (b) represents the first-order derivative curve;

[0029] Figure 4 The water contact angle results of the composite films prepared in Examples 1 to 5 and Comparative Example 1 of the present disclosure are shown;

[0030] Figure 5 The anti-fog performance results of the composite films prepared in Examples 1 to 5 of the present disclosure and Comparative Example 1 are shown;

[0031] Figure 6 A bar chart showing the inhibition rates of five types of bacteria of the composite films prepared in Examples 1 to 5 of the present disclosure and Comparative Example 1;

[0032] Figure 7 The graph shows the test results of the freshness-keeping performance of the composite films prepared in Example 3 and Comparative Example 1 of the present disclosure on rapeseed. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0034] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present disclosure should have the common meanings understood by persons having ordinary skills in the field to which the present disclosure belongs.

[0035] The "range" used in the embodiments of the present disclosure is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 130 and 70 to 120 is listed for a particular parameter, it is understood that a range of 60 to 120 and 70 to 130 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present disclosure, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] If not otherwise specified, all embodiments and optional embodiments of the present disclosure may be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form a new technical solution.

[0038] If there is no special explanation, the "include" and "comprising" mentioned in the present disclosure represent open or closed forms. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0039] If not specifically stated, in the present disclosure, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B".

[0040] In the related art, the commonly used preservation methods for rapeseed are chemical preservation and physical preservation. Among them, chemical preservation mainly uses chemical preservatives (for example, 1-methylcyclopropene, ozone and calcium chloride, etc.) to fumigate and soak the rapeseed, which is easy to cause the residue of chemical components and endanger human health. Physical preservation mainly involves low-temperature storage and controlled atmosphere storage after wrapping with plastic wrap. When using packaging materials (such as plastic wrap, etc.) to wrap rapeseed, although it can alleviate the water loss of leaves to a certain extent, the moisture produced by the respiration of rapeseed cannot be discharged in time, and it is easy to form water droplets on the surface of the plastic wrap and drip on the surface of the leaves, causing the growth of corrupt microorganisms and the rot of the leaves. In addition, petroleum-based plastic wrap is not easy to degrade, and excessive use will cause serious environmental pollution.

[0041] In view of this, the embodiments of the present disclosure provide a composite film, a preparation method and an application. Specifically, the composite film includes 30 to 70 parts of pectin, 400 to 500 parts of chitosan quaternary ammonium salt, 0.03 to 0.7 parts of riboflavin, 300 to 400 parts of glycerol and 100 to 200 parts of water. The composite film is formed by pectin, chitosan quaternary ammonium salt, riboflavin and glycerol, so that the composite film has excellent moisture absorption, anti-fog and antibacterial effects, and can reduce the possibility of water condensation generated by the respiration of fruits and vegetables while avoiding the loss of water and wilting of fruits and vegetables, and inhibit the growth of microorganisms, thereby extending the shelf life of fruits and vegetables.

[0042] In a first aspect, an embodiment of the present disclosure provides a composite film comprising 30 to 70 parts of pectin, 400 to 500 parts of chitosan quaternary ammonium salt, 0.03 to 0.7 parts of riboflavin, 300 to 400 parts of glycerol and 100 to 200 parts of water.

[0043] Here, pectin and chitosan quaternary ammonium salts as film-forming matrices are biodegradable, which fundamentally solves the problem that petroleum-based cling film is not easy to degrade and easily causes white pollution to the environment. The addition of riboflavin can not only play its own antibacterial and anti-ultraviolet effects, but also reduce the water contact angle of the composite film, improve the hydrophilicity, and make the composite film have excellent moisture absorption, anti-fog and antibacterial effects. It can reduce the possibility of condensation of water produced by the respiration of fruits and vegetables while avoiding the loss of water and wilting of fruits and vegetables, thereby reducing the possibility of water droplets dripping on the surface of fruits and vegetables to breed microorganisms, while inhibiting the growth of microorganisms, further extending the shelf life of fruits and vegetables.

[0044] In some embodiments, the water contact angle of the composite film does not exceed 67°, such as 66°, 60°, 53°, 50°, 48°, 46°, etc. Compared with the composite film without riboflavin, the composite film provided by the embodiment of the present disclosure has a smaller water contact angle, which is conducive to absorbing moisture and preventing water mist condensation.

[0045] In some optional embodiments, the composite film includes 50-60 parts of pectin, 430-460 parts of chitosan quaternary ammonium salt, 0.1-0.2 parts of riboflavin, 330-360 parts of glycerol and 120-170 parts of water.

[0046] In some optional embodiments, the composite film includes 50-60 parts of pectin, 430-460 parts of chitosan quaternary ammonium salt, 0.1-0.2 parts of riboflavin, 330-360 parts of glycerol and 120-170 parts of water.

[0047] In some optional embodiments, the composite film includes 55-57 parts of pectin, 440-450 parts of chitosan quaternary ammonium salt, 0.1-0.15 parts of riboflavin, 350-360 parts of glycerol and 140-150 parts of water. Such a composite film not only has excellent moisture absorption, anti-fogging and antibacterial effects, but also has excellent mechanical properties.

[0048] In a second aspect, the present disclosure also provides a method for preparing a composite film, comprising:

[0049] S1: dissolving chitosan quaternary ammonium salt, pectin and riboflavin in water respectively to obtain chitosan quaternary ammonium salt solution, pectin solution and riboflavin solution;

[0050] S2: at a preset temperature, adding pectin solution, riboflavin solution and glycerol to the chitosan quaternary ammonium salt solution in sequence, and mixing in the dark to obtain a mixed solution;

[0051] S3: Casting and drying the mixed solution after removing bubbles to obtain the composite film.

[0052] It should be noted that the water content of the composite film is not higher than 20%, for example, 15%, 14%, 13%, etc. If the water content of the composite film is higher than 20%, the structure thereof is not stable enough.

[0053] In some embodiments, the mass concentration of chitosan quaternary ammonium salt in the chitosan quaternary ammonium salt solution is 0.015 g / mL to 0.025 g / mL, optionally 0.02 g / mL.

[0054] In some embodiments, the mass concentration of pectin in the pectin solution is 0.005 g / mL to 0.015 g / mL. Optionally, it is 0.01 g / mL. It should be noted that in order to better dissolve pectin, pectin solid powder can be dissolved in heated water to prepare a pectin solution. Here, the temperature of the water can be 45°C to 55°C, such as 50°C, 52°C, etc., preferably 50°C.

[0055] In some embodiments, the mass concentration of riboflavin in the riboflavin solution is 0.1-0.2 mg / mL, optionally 0.125 mg / mL. The temperature of the water dissolving the riboflavin is 50°C-60°C, such as 50°C, 53°C, 55°C, 57°C, 60°C, etc., preferably 55°C.

[0056] It should be noted that the water in each solution in step S1 is double distilled water or distilled water, preferably distilled water. In the process of preparing the above solutions, magnetic stirring and dissolution can be performed with the aid of a magnetic stirrer. There is no special requirement for magnetic stirring, and it is only necessary to dissolve all the solid powders.

[0057] In some embodiments, the preset temperature is 45°C to 55°C, preferably 50°C.

[0058] In some embodiments, the volume ratio of the chitosan quaternary ammonium salt solution to the pectin solution in step S2 is 1:0.11 to 1:0.66, optionally 1:0.25.

[0059] In some embodiments, the volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the glycerol is 1:0.005 to 1:0.02, optionally 1:0.01.

[0060] In some embodiments, the volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the riboflavin solution is 1:0.001 to 1:0.20, optionally 1:0.009 to 1:0.18.

[0061] The use of a mixed liquid having the above-mentioned temperature and volume ratio relationship is helpful to obtain a composite film having excellent mechanical properties, high thermal stability and the ability to effectively reduce the water contact angle.

[0062] Furthermore, step S2 is mixed by magnetic stirring; wherein the magnetic stirring time is 20 min to 40 min, optionally 30 min; the rotation speed is 200 rpm / min to 500 rpm / min, optionally 400 rpm / min.

[0063] In some embodiments, in step S3, bubbles are removed by ultrasound; wherein the power of the ultrasound is 200W to 500W, optionally 300W; and the time is 10min to 30min, optionally 15min.

[0064] In some embodiments, the drying temperature is 20° C. to 60° C., optionally 40° C.; the drying time is 10 h to 30 h, optionally 24 h.

[0065] In some embodiments, the cast support may be an acrylic plate.

[0066] In a second aspect, the embodiments of the present disclosure also provide the use of any of the aforementioned composite films or any of the preparation methods to obtain the composite films in food packaging, for example, to preserve fruits and vegetables, which has anti-fog and antibacterial effects and can effectively extend the shelf life of food.

[0067] In order to make the technical solution of the present disclosure clearer and easier to understand, the composite film, preparation method and application provided by the embodiments of the present disclosure are introduced below with reference to the accompanying drawings.

[0068] Example 1

[0069] S1: Weigh 2.0g of chitosan quaternary ammonium salt solid powder and dissolve it in about 100mL of distilled water to obtain a 0.02g / ml chitosan quaternary ammonium salt solution; weigh 1.0g of pectin solid powder and dissolve it in about 100mL of distilled water at a temperature of 50°C to obtain a 0.01g / ml pectin solution; weigh 5mg of riboflavin solid powder and dissolve it in about 40mL of distilled water at a temperature of 55°C to obtain a 0.125mg / mL riboflavin solution.

[0070] S2: Heat 16 mL of chitosan quaternary ammonium salt solution to 50°C, add 4 mL of pectin solution, 0.18 mL of riboflavin solution and 0.2 mL of glycerol in sequence, and stir magnetically at 400 rpm / min at 50°C for 30 min using a heating magnetic stirrer in a dark environment to obtain a uniform mixed solution.

[0071] S3: The mixed solution was ultrasonicated for 15 minutes at a power of 300 W to remove bubbles in the mixed solution, and then cast onto an acrylic plate, heated and dried at 40° C. for 24 hours, and the obtained film was peeled off for use, and recorded as HP4-0.05. The moisture content of HP4-0.05 was 16.3%.

[0072] Example 2

[0073] The film was prepared according to the method described in Example 1, except that the volume of the riboflavin solution added was changed from 0.18 mL to 0.36 mL, and the film was peeled off and used for later use, and was recorded as HP4-0.1. The moisture content of HP4-0.1 was 15.3%.

[0074] Example 3

[0075] The film was prepared according to the method described in Example 1, except that the volume of the riboflavin solution added was changed from 0.18 mL to 0.72 mL, and the obtained film was peeled off and used for later use, and was recorded as HP4-0.2. The moisture content of HP4-0.2 was 14.6%.

[0076] Example 4

[0077] The film was prepared according to the method described in Example 1, except that the volume of the riboflavin solution added was changed from 0.18 mL to 1.8 mL, and the film was peeled off and used for later use, and was recorded as HP4-0.5. The moisture content of HP4-0.5 was 13.8%.

[0078] Example 5

[0079] A film was prepared according to the method described in Example 1, except that the volume of the riboflavin solution added was changed from 0.18 mL to 3.6 mL, and the obtained film was peeled off and set aside for later use, and was recorded as HP4-1. The moisture content of HP4-1 was 13.2%.

[0080] Comparative Example 1

[0081] S1: Weigh 2.0g chitosan quaternary ammonium salt solid powder and dissolve it in 100mL distilled water to prepare 0.02g / ml chitosan quaternary ammonium salt solution. Weigh 1.0g pectin solid powder and dissolve it in 100mL distilled water at 50℃ to prepare 0.01g / ml pectin solution. Weigh 5mg riboflavin solid powder and dissolve it in 40mL distilled water at 55℃ to prepare 0.125mg / mL riboflavin solution.

[0082] S2: Heat 16 mL of chitosan quaternary ammonium salt solution to 50°C, add 4 mL of pectin solution and 0.2 mL of glycerol in sequence, and stir magnetically at 400 rpm / min at 50°C for 30 min using a heating magnetic stirrer in a dark environment to obtain a uniform mixed solution.

[0083] S3: The mixed solution was ultrasonicated for 15 minutes at a power of 300 W to remove bubbles therein, and then cast onto an acrylic plate, heated and dried at 40° C. for 24 hours, and the obtained film was peeled off for later use, and was recorded as HP4. The moisture content of HP4 was 15.5%.

[0084] The composite films prepared in Examples 1-5 and Comparative Example 1 were cut into square shapes of the same size as the school emblem, with the colored school emblem image as the bottom background, and the cut films were covered on the right 1 / 2 of the colored school emblem image. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that as the amount of riboflavin added increases, the yellow color of the composite film gradually increases. It should be understood that the stronger the yellow color, the stronger the composite film's resistance to ultraviolet rays.

[0085] Test Example 1

[0086] The mechanical properties of the films prepared in Examples 1-5 and Comparative Example 1 were tested

[0087] The film was cut into rectangular strips (100 × 10 mm). The tensile strength and elongation at break of the film were measured by a universal tensile testing machine with an initial clamp distance of 30 mm and a tensile speed of 5 mm / s. The test results are shown in Figure 2 shown.

[0088] like Figure 2 As shown, after chitosan quaternary ammonium salt and pectin are mixed, hydrogen bonds are formed between the amino groups carried by chitosan quaternary ammonium salt and the carboxyl groups carried by pectin, the intermolecular forces are enhanced, and the tensile strength of the film is high (about 33.30MPa). As the amount of riboflavin added gradually increases, the tensile strength shows a trend of fluctuating downward, and the elongation at break shows a trend of fluctuating upward. This may be that the addition of riboflavin affects the hydrogen bond-stabilized structure formed between the matrices, but the tensile strength and elongation at break of the composite film can still meet the requirements of packaged food. Among them, the tensile strength of HP4-0.2 is 32.09MPa, which is close to the comparative example 1 without adding riboflavin, and the elongation at break is 107.1%, which is much higher than the comparative example 1, and the mechanical properties are optimal.

[0089] Test Example 2

[0090] Test the thermal stability of the composite films prepared in Examples 1-5 and Comparative Example 1

[0091] The thermal stability of the composite film was measured using a thermogravimetric analyzer. A 10 mg composite film sample was placed in an alumina pan and heated from 25°C to 600°C at a rate of 10°C / min to test its thermal stability in high-purity nitrogen. The first-order derivative analysis of the obtained thermogravimetric curve was performed to analyze the effect of riboflavin addition on the weight loss rate of the composite film.

[0092] like Figure 3 As shown, the thermal stability was evaluated by the weight loss of the composite film during heating. Figure 3The decomposition of the composite film went through three steps: the first step was 25℃~140℃, and the weight loss in this stage was mainly due to the evaporation of free water in the composite film; the second step was 140℃~240℃, and the weight loss in this stage was mainly caused by the volatilization of bound water and the degradation of glycerol in the composite film; the third step was 240℃~400℃, which was the main step for the weight loss of the composite film, mainly due to the thermal degradation of chitosan quaternary ammonium salt and pectin polymer chain and the decomposition of riboflavin molecular chain, and the maximum weight loss temperature was about 260℃. After adding riboflavin to the composite film matrix, the weight loss of the composite film at 227℃ was significantly reduced. The increase in decomposition temperature indicates that the addition of riboflavin can enhance the thermal stability of the composite film. At 600℃, the residual material left after the composite film was decomposed was about 20%, and the residual mass of the composite film with riboflavin added was higher than that of the HP4 film, among which HP4-0.2 had the largest residual amount (22.16%). This shows that the thermal stability of the composite film is improved after the addition of riboflavin.

[0093] Test Example 3

[0094] Test the water contact angle of the composite films prepared in Examples 1-5 and Comparative Example 1

[0095] The water contact angle was measured by the water drop method. The film sample (2 cm×2 cm) was fixed on the contact angle measuring instrument. 10 μL of water was dropped on the surface of the composite film, and the water contact angle of the composite film was measured at 60 seconds.

[0096] like Figure 4 As shown, the water contact angle can be used to evaluate the hydrophilic and hydrophobic properties of the anti-fog composite film. Figure 4 The water contact angles of composite films containing different concentrations of riboflavin are shown. All composite films are hydrophilic, but the water contact angle of HP4 is 74.632°, which has poor hydrophilic properties. After adding riboflavin, the water contact angles are significantly reduced, and HP4-0.5 is only 46.869°. The hydrophilic properties of the composite films are enhanced, indicating that the addition of riboflavin will change the original structure and surface smoothness of the composite film. In addition, the lower water contact angle is conducive to the formation of a uniform water layer on the surface of the film by water vapor, rather than agglomerating into water droplets, which is why the composite film has an anti-fog function.

[0097] Test Example 4

[0098] Test the anti-fogging properties of the composite films prepared in Examples 1-5 and Comparative Example 1

[0099] The anti-fog performance of the composite film was tested by the cold fog method. In the cold fog method test, the composite film was covered on the top of a beaker filled with distilled water and placed in a 4°C refrigerator. Photos were taken after 5 minutes, 1 hour, and 3 hours to record the state of the composite film. The results are as follows: Figure 5Ordinary cling film commonly used in the market was used as the control group (CK group).

[0100] When composite films are used as packaging materials, especially when packaging products with self-breathing functions such as fruits and vegetables, fog droplets or water droplets will form on the surface. The packaging composite film with anti-fog function can maintain a transparent state and ensure the visual effect of the packaged products. The cold fog method is used to evaluate the anti-fog effect of the composite film. Figure 5 As shown in the figure, at the beginning, the composite films of the control group (commercially available composite film) and the experimental group (composite film) remained transparent, and the school emblem picture at the bottom of the beaker was clearly visible. After the beaker was placed in a 4°C refrigerator for 3 hours, the surface of the composite film of the CK group was fogged, and the picture at the bottom of the beaker could not be seen clearly, while no obvious changes occurred in the other groups. This is attributed to the fact that the composite film can quickly spread the water vapor condensed on the surface, achieving an anti-fog effect. Figure 5 In the scale, 1 means completely transparent without water droplets; 2 means relatively good transparency with a small amount of water droplets; 3 means basically transparent with more water droplets; 4 means semi-transparent with many small water droplets; 5 means completely opaque.

[0101] Test Example 5

[0102] Test the antibacterial properties of the composite films prepared in Examples 1-5 and Comparative Example 1

[0103] Bacillus subtilis, Escherichia coli, Pseudomonas fluorescens, Staphylococcus aureus and Erwinia were inoculated into liquid culture medium and cultured at the optimum temperature for 24 h. 8 CFU / mL formed bacterial suspension. 100μL bacterial suspension and 100μL membrane solution were added to a 96-well plate, and the absorbance at 600nm was measured at 0h and 9h respectively. The culture medium was used as a blank control. The inhibition rate of the composite film was calculated according to the following formula:

[0104]

[0105] Among them, Abs0, Abs9 and Abs 空白 They represent the concentration of each well at 0 h, the concentration of each well at 9 h and the concentration of the control group at 9 h respectively.

[0106] The antibacterial properties of the membrane solution were evaluated by testing its inhibitory effect on five strains. Figure 6As shown in the figure, HP4 film showed weak inhibition performance against the five tested strains. This is because the positive charge carried by the chitosan quaternary ammonium salt acts on the negative charge on the surface of the bacterial cell membrane, causing the death of the bacteria. After adding riboflavin, the antibacterial effect of the film was significantly enhanced. The inhibition rate of HP4-0.2 against Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Pseudomonas fluorescens and Erwinia reached 90%. In addition, the antibacterial effect also showed a dose-dependent relationship with the concentration of riboflavin.

[0107] Based on test examples 1 to 4, it can be seen that the HP4-0.2 composite film has excellent anti-fog and antibacterial properties, as well as good mechanical properties. Adhering to the principle of maintaining performance and reducing costs, the HP4-0.2 composite film (Example 3) was used to carry out subsequent preservation tests.

[0108] Test Example 6

[0109] Test on the freshness-keeping performance of anti-fog and antibacterial composite film

[0110] Rapeseeds of the same size and without mechanical damage were selected as experimental materials. Three experimental groups were set up, namely: (1) CK group: no treatment; (2) BX group: wrapped and sealed with commercially available plastic wrap; (3) HPR group: wrapped and sealed with the HP4-0.2 composite film prepared in Example 3. The sealed rapeseeds of each group were placed in a refrigerator and stored at 4°C. The rapeseeds were photographed on the 0th, 2nd, 5th, 8th and 11th days to observe their appearance.

[0111] like Figure 7 As shown in the figure, the rapeseed in the HPR group wilted on the 11th day, while the CK group wilted due to water loss on the 5th day. The leaves of the CK group and the BX group turned yellow on the 5th and 8th day, respectively, indicating that the chlorophyll gradually degraded; while the leaves of the HPR group began to turn yellow on the 11th day. This shows that the composite film can effectively extend the shelf life of rapeseed and delay the degradation of chlorophyll.

[0112] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Based on the concept of the present disclosure, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present disclosure as described above, which are not provided in detail for the sake of simplicity.

[0113] The embodiments of the present disclosure are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A composite film, characterized in that: The invention comprises 30-70 parts of pectin, 400-500 parts of chitosan quaternary ammonium salt, 0.03-0.7 parts of riboflavin, 300-400 parts of glycerol and 100-200 parts of water.

2. The composite film according to claim 1, characterized in that The composite film comprises 50-60 parts of pectin, 430-460 parts of chitosan quaternary ammonium salt, 0.1-0.2 parts of riboflavin, 330-360 parts of glycerol and 120-170 parts of water.

3. The composite film according to claim 1, characterized in that The water contact angle of the composite film is no more than 67°.

4. A method for preparing a composite film, characterized in that: include: S1: dissolving chitosan quaternary ammonium salt, pectin and riboflavin in water respectively to obtain chitosan quaternary ammonium salt solution, pectin solution and riboflavin solution; S2: at a preset temperature, adding pectin solution, riboflavin solution and glycerol to the chitosan quaternary ammonium salt solution in sequence, and mixing in the dark to obtain a mixed solution; S3: Casting and drying the mixed solution after removing bubbles to obtain the composite film.

5. The preparation method according to claim 4, characterized in that: The mass concentration of chitosan quaternary ammonium salt in the chitosan quaternary ammonium salt solution is 0.015 g / mL to 0.025 g / mL; and / or The mass concentration of pectin in the pectin solution is 0.005 g / mL to 0.015 g / mL; wherein the temperature of the water dissolving the pectin is 45° C. to 55° C.; and / or; The mass concentration of riboflavin in the riboflavin solution is 0.1-0.2 mg / mL, wherein the temperature of the water dissolving the riboflavin is 50° C.-60° C.

6. The preparation method according to claim 4, characterized in that: The water content of the composite film is not higher than 20%.

7. The preparation method according to claim 4, characterized in that: The volume ratio of the chitosan quaternary ammonium salt solution to the pectin solution in step S2 is 1:0.11 to 1:0.66; and / or The volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the glycerol is 1:0.005 to 1:0.02; and / or The volume ratio of the total volume of the chitosan quaternary ammonium salt solution and the pectin solution to the riboflavin solution is 1:0.001 to 1:0.20; and / or The preset temperature is 45°C to 55°C.

8. The preparation method according to claim 4, characterized in that: Step S2 is to mix by magnetic stirring; wherein the magnetic stirring time is 20min to 40min, and the rotation speed is 200rpm / min to 500rpm / min.

9. The preparation method according to claim 4, characterized in that: In step S3, the bubbles are removed by ultrasound; wherein the power of the ultrasound is 200W to 500W and the time is 10min to 30min; and / or The drying temperature is 20°C to 60°C and the drying time is 10h to 30h; and / or The carrier for the casting is an acrylic plate.

10. Use of the composite film according to any one of claims 1 to 3 or the composite film obtained by the preparation method according to any one of claims 4 to 9 in food packaging.

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