Preparation method of waterproof, oil-resistant and antibacterial composite film and application of waterproof, oil-resistant and antibacterial composite film in preservation of livestock and poultry prefabricated vegetables

Abstract

The invention discloses a preparation method of a waterproof, oil-resistant and antibacterial composite film and application of the waterproof, oil-resistant and antibacterial composite film in preservation of livestock and poultry prefabricated vegetables. The preparation method comprises the following steps: uniformly mixing a starch aqueous solution and an ethanol solution of chitosan, adding glycerol, cinnamyl aldehyde and nano-zinc oxide, and stirring at room temperature to obtain a uniform mixed membrane solution A; dissolving polyvinyl butyral and ethyl cellulose in absolute ethyl alcohol, heating and stirring to obtain a uniform mixed membrane solution B; pouring the mixed film solution B, drying at room temperature to obtain a waterproof layer, then pouring the mixed film solution A, standing at room temperature to obtain an antibacterial functional layer, finally pouring the mixed film solution B, and drying to obtain the waterproof, oil-resistant and antibacterial composite film. The waterproof layer is prepared by taking starch, chitosan, glycerol, cinnamyl aldehyde and nano-zinc oxide as raw materials; preparing an oil-resistant and antibacterial layer from polyvinyl butyral and ethyl cellulose; the composite film has waterproof, oil-resistant and bacteriostatic capabilities, and can be used for fresh-keeping of livestock and poultry prefabricated vegetables.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of food packaging and technology, and particularly relates to a preparation method of a waterproof, oil-resistant and antibacterial composite film and application of the film in preservation of livestock and poultry prepared dishes. BACKGROUND

[0002] Prepared dishes generally refer to dishes prepared by using agricultural, livestock, poultry and aquatic products as raw materials, and then stored, transported and sold under normal temperature, cold storage or freezing conditions, and the dishes can be directly eaten or simply processed before eating. Livestock and poultry prepared dishes are rich in nutrients, but are easily contaminated by microorganisms, thus resulting in a short shelf life, resource waste and economic loss. In recent years, it has been found that active films with antibacterial effect can be used for food packaging, which can effectively reduce the damage to the texture and flavor of food during processing while prolonging the shelf life of food. As a biological base film for packaging food, it needs to have good barrier properties and water resistance. However, the biological base film prepared by a single film-forming matrix often has poor waterproof and oil resistance, and is difficult to meet the requirements of food packaging such as livestock and poultry prepared dishes with high fat content. At the same time, ordinary biological base films do not have antibacterial properties, and the above shortcomings limit their application in the field of food packaging such as livestock and poultry prepared dishes. Therefore, it is necessary to prepare a composite packaging film with waterproof and oil-resistant properties and antibacterial properties.

[0003] Corn starch is a natural polymer compound widely existing in nature, which is renewable, biodegradable, easy to obtain and low in price. It can form a film alone and has excellent oil barrier property, but the mechanical properties and moisture barrier properties of natural starch film alone are poor, and the brittleness is large, which limits its application in many fields. Chitosan is a natural polymer compound, which has been widely used in packaging field in recent years due to its good film forming property, oil barrier property, biocompatibility and biodegradability. Chitosan and starch are compounded to form hydrogen bonds inside, thereby improving the performance of the film. Nano zinc oxide has abundant raw material resources, excellent antibacterial property, outstanding heat resistance and stability, long antibacterial duration, no toxicity to human cells and good biocompatibility. It can be used as a food antibacterial agent. Since chitosan also has antibacterial property, chitosan is added in many composite films at present, such as the patent with the application number 201910671111.8 discloses a preparation method of edible antibacterial film, which is prepared from starch, chitosan and ZnO. However, pre-prepared dishes are easily contaminated by microorganisms, so the antibacterial requirement of the protective film is high. Cinnamaldehyde is the main active ingredient of cinnamon essential oil and a common natural antibacterial agent extracted from cinnamon. It has broad-spectrum antibacterial property and strong inhibitory effect on bacteria, molds and yeasts, and is applied in the field of food additives. However, the high volatility of cinnamaldehyde leads to rapid loss of effective components, which limits its application in the food industry. Therefore, how to add cinnamaldehyde to the composite film and overcome the high volatility to improve the antibacterial rate of the composite film is a problem to be solved. SUMMARY

[0004] In view of the above prior art, the purpose of the present application is to provide a preparation method of waterproof, oil-resistant and antibacterial composite film and its application in preservation of pre-prepared dishes of livestock and poultry. The present application prepares an oil-resistant and antibacterial layer by using starch, chitosan, glycerol, cinnamaldehyde and nano zinc oxide as raw materials; and a waterproof layer by using polyvinyl butyral and ethyl cellulose, so that the composite film has the ability of waterproofing, oil resistance and antibacterial property, and can be used for preservation of pre-prepared dishes of livestock and poultry.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows: In the first aspect of the present application, a preparation method of waterproof, oil-resistant and antibacterial composite film is provided, (1) starch and chitosan are respectively dissolved in deionized water and acetic acid solution to prepare starch solution and chitosan solution; the two solutions are mixed uniformly, and then glycerol, cinnamaldehyde and nano zinc oxide are added, and stirred at room temperature to obtain a uniform mixed film liquid A; (2) polyvinyl butyral and ethyl cellulose are dissolved in anhydrous ethanol, heated and stirred to obtain a uniform mixed film liquid B; (3) Pouring mixed film liquid B, drying at room temperature to obtain a waterproof layer, then pouring mixed film liquid A, placing at room temperature to obtain an antibacterial functional layer, and finally pouring mixed film liquid B to prepare a waterproof, oil-resistant and bacteriostatic composite film after drying.

[0006] Preferably, in step (1), the volume concentration of the acetic acid solution is 2%; the mass concentration of the powder solution is 3%; and the mass concentration of the chitosan solution is 1%.

[0007] Preferably, in step (1), the volume ratio of the starch solution and the chitosan solution is 5:4; and the mass ratio of the starch and the chitosan is 3:1.

[0008] Preferably, in step (1), the added amount of glycerol accounts for 35% of the total mass of the starch and the chitosan; the added amount of nano-zinc oxide accounts for 0.05-0.2% of the total mass of the starch and the chitosan; the added amount of cinnamyl aldehyde accounts for 4% of the total mass of the starch and the chitosan; and the stirring time is 2h.

[0009] Preferably, in step (2), the added amounts of polyvinyl butyral, ethyl cellulose and anhydrous ethanol are in the ratio of 6g:4g:125mL.

[0010] Preferably, in step (2), the heating temperature is 50℃, and the heating time is 1h.

[0011] Preferably, in step (3), the drying time at room temperature is 2h; and the standing time at room temperature is 48h.

[0012] In a second aspect of the present application, a waterproof, oil-resistant and bacteriostatic composite film is provided, which comprises, from bottom to top, a first waterproof layer, an oil-resistant and bacteriostatic functional layer, and a second waterproof layer; the first waterproof layer and the second waterproof layer are obtained by pouring mixed film liquid B; and the oil-resistant and bacteriostatic functional layer is obtained by pouring mixed film liquid A.

[0013] Preferably, the thickness of the first waterproof layer and the second waterproof layer is 0.05mm; and the thickness of the oil-resistant and bacteriostatic functional layer is 0.06mm.

[0014] In a third aspect of the present application, the waterproof, oil-resistant and bacteriostatic composite film is applied to the preservation of pre-prepared dishes for livestock and poultry.

[0015] The present application has the following advantages: (1) The composite film prepared in the present application is waterproof due to the blending of polyvinyl butyral and ethyl cellulose. (2) The composite film has oil-resistant performance due to the blending of starch and chitosan.

[0016] (3) The added cinnamyl aldehyde has broad-spectrum bacteriostasis and oxidation resistance, can effectively inhibit the growth of microorganisms in the package, and prolong the shelf life; (4) The good dispersibility and good interface adhesion of the nano zinc oxide particles in the composite material can prolong the service life of the film, and in addition, the addition of the nano zinc oxide particles enhances the antibacterial effect of the composite film. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Fig. 1 is a mechanical property diagram of the composite film prepared in Examples 1-5 of the present application; Figure 2 Fig. 2 is a barrier property diagram of the composite film prepared in Examples 1-5 of the present application; Figure 3 Fig. 3 is a water solubility diagram of the composite film prepared in Examples 1-5 of the present application; Figure 4 Fig. 4 is an antibacterial property diagram of the composite film prepared in Examples 1-5 of the present application on Staphylococcus aureus and Escherichia coli, wherein (a) is a photo of the antibacterial circle of the composite film on Escherichia coli (upper) and Staphylococcus aureus (lower) with the addition amount of nano zinc oxide being 0.20%, 0.15%, 0.10%, 0.05% and 0 (from left to right), and (b) is the antibacterial circle diameter of the composite film on Escherichia coli and Staphylococcus aureus; Figure 5 Fig. 5 is a diagram of the total number of colonies of the composite film prepared in Examples 1-5 of the present application and the ordinary PE film on the packaged red-braised meat pre-prepared dish. DETAILED DESCRIPTION

[0018] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0019] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with specific examples.

[0020] The test materials used in the examples of the present application are all conventional test materials in the art and can be purchased through commercial channels.

[0021] Example 1: Preparation of waterproof, oil-resistant and antibacterial composite film (1) 1 g of chitosan was weighed and dissolved in 2% (volume fraction) aqueous glacial acetic acid to obtain a chitosan acetic acid solution with a mass concentration of 1%. 3 g of corn starch was weighed and added to distilled water to obtain a starch solution with a mass concentration of 3%. The solution was heated to 90°C under magnetic stirring and gelatinized for 30 min. Then 1.05 mL of glycerol was added and stirred for 30 min to obtain a gelatinized starch solution. The chitosan solution and the starch solution were mixed in a ratio of 5:4 to obtain a starch-chitosan solution. 1.45 mL of cinnamyl aldehyde and 0.72 mL of Tween 80 were added to 90 mL of the mixed starch-chitosan solution. Then 0.15% of nano-zinc oxide based on the total mass of starch and chitosan was added. The mixture was stirred magnetically for 2 h to obtain a mixed film solution A.

[0022] (2) 6 g of polyvinyl butyral and 4 g of ethyl cellulose were dissolved in 125 mL of anhydrous ethanol. The mixture was stirred at 50°C for 1 h to obtain a uniform mixed film solution B.

[0023] The mixed film solution B was poured into a plastic culture dish (15 cm x 15 cm) and dried at room temperature for 2 h to obtain a first waterproof layer. Then the mixed film solution A was poured into a plastic culture dish (15 cm x 15 cm) and dried at room temperature for 48 h to obtain an oil-resistant and antibacterial functional layer. Then a layer of mixed film solution B was poured to obtain a second waterproof layer. After drying, a waterproof, oil-resistant and antibacterial composite film was prepared, which was named as CSC-ZnO3 film. The thickness of the first and second waterproof layers was 0.05 mm, and the thickness of the oil-resistant and antibacterial functional layer was 0.06 mm.

[0024] Example 2 The difference from Example 1 is that the amount of nano-zinc oxide added in step (2) is 0.20% based on the total mass of starch and chitosan. The other steps and parameters are the same. The obtained film is named as CSC-ZnO4 film.

[0025] Example 3 The difference from Example 1 is that the amount of nano-zinc oxide added in step (2) is 0.10% based on the total mass of starch and chitosan. The other steps and parameters are the same. The obtained film is named as CSC-ZnO2 film.

[0026] Example 4 The difference from Example 1 is that the amount of nano-zinc oxide added in step (2) is 0.05% based on the total mass of starch and chitosan. The other steps and parameters are the same. The obtained film is named as CSC-ZnO1 film.

[0027] Example 5 The difference from Example 1 is that the amount of nano-zinc oxide added in step (2) is 0. The other steps and parameters are the same. The obtained film is named as CSC film.

[0028] The composite films prepared in the above Examples 1-5 were subjected to relevant performance tests.

[0029] (1) Test of mechanical properties: The film thickness was measured using a micrometer with an accuracy of 0.001 mm. Random points were taken on each film, and the average value was taken as the final result. The tensile test was performed using a universal tensile testing machine (Model XLW, Labthink Instruments Co., Ltd., Jinan, China). The film was cut into a strip with a size of 70 mm x 10 mm, and the test was performed on the film in a dry state. The initial clamping distance of the probe was 100 mm, and the probe moving speed was 100 mm / min. Each type of film was tested three times, and the average value was taken. The tensile strength (TS) and elongation at break (EAB) were calculated according to the following formulas: In the formula, F represents the force; S represents the cross-sectional area of the film; L represents the length of the film after stretching; and L0 represents the initial length of the film.

[0030] The results are shown in Table 1. Figure 1 As shown in Table 1, the composite films prepared in Examples 1-5 of the present application had good tensile strength and elongation at break. With the increase of the amount of added nano-zinc oxide, the tensile strength gradually increased, and the elongation at break gradually decreased. The tensile strength increased from 6.06 MPa to 9.47 MPa, and the elongation at break decreased from 55.73 MPa to 17.86 MPa.

[0031] (2) Test of barrier properties: The oxygen permeability of the film was determined using a C106H gas permeation instrument. The PERME TM The water vapor permeability of the antioxidant film was determined using a W3 / 030 water vapor transmission rate tester. Each group of samples was measured three times, and the average value was taken. The oxygen transmission rate (OTR) and the water vapor transmission rate (WVTR) were calculated according to the following formulas: The results are shown in Table 2. Figure 2 As shown in Table 2, with the increase of the content of nano-zinc oxide, the oxygen transmission rate and the water vapor transmission rate of the composite film were reduced. The oxygen transmission rate and the water vapor transmission rate were reduced from 8.26 (x 10 -6 cm 2 ·cm·cm -2 ·s -1 ·Pa -1 ) to 4.02 (x 10 -6 cm 2 ·cm·cm -2 ·s -1 ·Pa -1 ) and 4.06 (x 10-13 g·m -1 ·s -1 ·pa -1 ) to 3.44 (x 10 -13 g·m -1 ·s -1 ·pa -1 ). Therefore, the composite film has better oxygen and water vapor barrier ability, which is beneficial to the application of food packaging.

[0032] (3) Water-soluble test: The film was cut into 2 cm x 2 cm square samples, and was baked in an oven at 105 ℃ to a constant mass, denoted as m0. Then the film was placed in 50 mL distilled water, and was left at room temperature for 24 h. After that, the film was taken out and baked in an oven at 105 ℃ to a constant mass, denoted as m1 (g). The water solubility was calculated as follows: As shown in Table 1, all the composite films have excellent oil resistance, and the oil-proof grade is 7. Figure 3 As shown in Table 1, with the increase of the content of nano zinc oxide, the water solubility of the composite film showed a significant decreasing trend. From 4.08% to 0.2%.

[0033] (4) Oil resistance test: Castor oil, n-heptane and toluene were configured into test solutions in a certain proportion to form 12 kinds of test solutions with various surface tensions. The grades were dropped from high to low at a distance of 25 mm from the composite film, and after 15 s, the back of the composite film was observed for discoloration due to penetration. The results are shown in Table 1.

[0034] Table 1 Test results of oil-proof grade of composite film As shown in Table 1, all the composite films have excellent oil resistance, and the oil-proof grade is 7.

[0035] (5) Bacteriostatic performance test: Staphylococcus aureus (gram-positive bacteria) and Escherichia coli (gram-negative bacteria) were used as experimental bacteria to test the bacteriostatic activity of the sample. The Escherichia coli and Staphylococcus aureus bacterial solution were diluted to 10 8 CFU / mL with sterile sodium chloride solution, and then 100 μL was taken and uniformly coated on the LB solid culture medium. The film sample was cut into a 6 mm diameter disc for testing, and was attached to the surface of the culture medium, and was gently pressed with sterile tweezers to ensure full contact between the sample and the culture medium. The culture dish was placed in a constant temperature incubator at 37 ℃ for 24 h. After the culture was completed, a normal camera was used to take a picture and measure the size of the bacteriostatic circle.

[0036] As shown in Table 1, all the composite films have excellent oil resistance, and the oil-proof grade is 7. Figure 4As shown, the inhibition zone appeared around the periphery of all composite film samples, indicating that they all had inhibitory effect on the two bacteria. The inhibition zone diameter of the composite film containing only cinnamaldehyde was only 11.14 mm and 11.09 mm for E. coli and S. aureus, respectively. With the increase of the content of nano-zinc oxide, the inhibition zone diameter of the composite film for E. coli and S. aureus reached 23.06 mm and 23.01 mm, respectively. It showed that nano-zinc oxide and cinnamaldehyde played a synergistic antibacterial effect, which further improved the antibacterial performance of the composite film.

[0037] (6) Total bacterial count determination: According to GB 4789.2-2022, the plate culture method was used to determine the total bacterial count (TPA) of the red cooked pork pre-prepared dish. 1 g of sample was weighed into a sterile homogenization bag containing 9 mL of diluent, and was beaten for 1 min with a beating homogenizer to prepare a 1:10 sample homogenate. Then, 10-fold serial dilution of the sample homogenate was prepared. Two sample homogenates with appropriate dilutions were selected, 100 μL of sample homogenate was taken in a sterile culture dish, and the plate colony counting method was used for counting.

[0038] The results are shown in Figure 5 During storage, the total bacterial count of all samples showed an upward trend. The total bacterial count of the red cooked pork pre-prepared dish packaged with PE film reached 10 4 CFU / g on the 9th day, which exceeded the national standard. The total bacterial count of the red cooked pork pre-prepared dish packaged with CSC-ZnO3 film remained below 10 4 CFU / g on the 12th day, and the total bacterial count of the red cooked pork pre-prepared dish packaged with CSC-ZnO3 film changed slowly and was relatively close throughout the storage period, and remained at a low level. Therefore, the addition of nano-zinc oxide increased the antibacterial effect of the film, which could inhibit the growth of microorganisms in the red cooked pork pre-prepared dish and played a good preservation effect.

[0039] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a waterproof, oil-resistant, and antibacterial composite film, characterized in that, (1) Dissolve starch and chitosan in deionized water and acetic acid solution respectively to prepare starch solution and chitosan solution; mix the two solutions evenly, then add glycerol, cinnamaldehyde and nano zinc oxide, stir at room temperature to obtain uniform mixed film solution A; (2) Dissolve polyvinyl butyral and ethyl cellulose in anhydrous ethanol, heat and stir to obtain a uniform mixed film solution B; (3) Pour mixed membrane liquid B, dry at room temperature to obtain a waterproof layer, then pour mixed membrane liquid A, place at room temperature to obtain an antibacterial functional layer, and finally pour mixed membrane liquid B, and after drying, prepare a composite membrane that is waterproof, oil-resistant and antibacterial.

2. The preparation method according to claim 1, characterized in that, In step (1), the volume concentration of the acetic acid solution is 2%; the mass concentration of the powder solution is 3%; and the mass concentration of the chitosan solution is 1%.

3. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of the starch solution to the chitosan solution is 5:4; the mass ratio of the starch to the chitosan is 3:

1.

4. The preparation method according to claim 1, characterized in that, In step (1), the amount of glycerol added accounts for 35% of the total mass of starch and chitosan; the amount of nano zinc oxide added accounts for 0.05~0.2% of the total mass of starch and chitosan; the amount of cinnamaldehyde added accounts for 4% of the total mass of starch and chitosan; and the stirring time is 2h.

5. The preparation method according to claim 1, characterized in that, In step (2), the ratio of the amount of polyvinyl butyral, ethyl cellulose and anhydrous ethanol added is 6 g: 4 g: 125 mL.

6. The preparation method according to claim 1, characterized in that, In step (2), the heating temperature is 50°C and the heating time is 1 hour.

7. The preparation method according to claim 1, characterized in that, In step (3), the room temperature drying time is 2 hours; the room temperature standing time is 48 hours.

8. The waterproof, oil-resistant, and antibacterial composite film obtained by the preparation method according to any one of claims 1 to 7, characterized in that, From bottom to top, the layers are: a first waterproof layer, an oil-blocking and antibacterial functional layer, and a second waterproof layer; the first and second waterproof layers are obtained by casting the mixed film liquid B as described in any one of claims 1 to 7; the oil-blocking and antibacterial functional layer is obtained by casting the mixed film liquid A as described in any one of claims 1 to 7.

9. The waterproof, oil-resistant, and antibacterial composite membrane according to claim 8, characterized in that, The thickness of both the first and second waterproof layers is 0.05 mm; the thickness of the oil-blocking and antibacterial functional layer is 0.06 mm.

10. The waterproof, oil-resistant, and antibacterial composite film according to claim 8 or 9 is used in the preservation of pre-cooked meat and poultry dishes.

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