Biodegradable food preservative film as well as preparation method and application thereof

Abstract

The invention provides a biodegradable food preservative film as well as a preparation method and application thereof. The preservative film is a chitosan and polyvinyl alcohol composite film loaded with cinnamon oil microcapsules. The preparation method mainly comprises microcapsule preparation and film preparation. Wherein the microcapsule preparation comprises the following steps: dissolving beta-cyclodextrin, adding cassia oil, and stirring the mixture to form a microcapsule emulsion. And storing the emulsion in a refrigerator overnight. And on the second day, filtering the solution to collect a precipitate, washing and drying to obtain the microcapsule. The film preparation comprises the step of mixing a polyvinyl alcohol solution, a chitosan solution and glycerol according to a fixed proportion. Then, adding cassia oil microcapsules, and uniformly stirring to obtain a film-forming solution; and pouring the film forming liquid into a mold flat plate to prepare a film, thereby obtaining the antibacterial composite film. The tear strength of the prepared film is 21.18 N / mm < 2 > to 43.21 N / mm < 2 >, the elongation at break is 82.60% to 147.56%, and the antioxidant activity is 27.47% to 36.87%; the preservative has an obvious inhibiting effect on staphylococcus aureus and escherichia coli, and can effectively prolong the shelf life of fresh-cut fruits.

Description

Technical Field

[0001] The invention relates to the technical field of cling film, and in particular to a method for preparing an antibacterial and anti-oxidation cling film. Background Art

[0002] Fruits are widely grown and consumed around the world, however, the high water content of fruits makes them susceptible to mechanical damage, microbial activity and deterioration, resulting in a short shelf life. The deterioration of fruits throughout the supply chain from harvesting and processing to storage and distribution poses a major threat to food security. Therefore, packaging plays a very important role in the food industry, including storage, transportation, and protection of food from contamination, moisture and temperature. In particular, some fragile and perishable fruits will deteriorate quickly after harvest, so various methods need to be used to delay ripening. Therefore, it is necessary to develop plastic wrap with antibacterial and antioxidant functions to extend the shelf life of fruits.

[0003] At present, food packaging materials are mainly plastic materials, which are composed of petroleum-based polymers. There are many problems and disadvantages such as difficult degradation, poor recyclability and environmental pollution. Therefore, biodegradable and non-toxic polymer-based films have attracted the attention of researchers, such as hydroxypropyl methylcellulose, starch, sodium alginate and polyvinyl alcohol. Among them, chitosan is the product of the natural polysaccharide chitin with some acetyl groups removed. It has the characteristics of biocompatibility, non-toxicity, high biodegradability and good film-forming ability. Polyvinyl alcohol is a non-toxic water-soluble polymer. Due to its environmental friendliness, non-toxicity and biodegradability, it has attracted attention as a food packaging material.

[0004] The deterioration of perishable foods due to contamination by pathogenic and spoilage microorganisms or oxidative deterioration is common in our daily lives, and these foods are not suitable for human consumption. Therefore, adding antimicrobial agents to food packaging to delay food spoilage plays a very important role. Studies have shown that the components of essential oils exhibit significant antioxidant and antibacterial properties against various pathogenic microorganisms and food spoilage microorganisms. Cinnamon oil is a plant essential oil extracted from the bark of cinnamon trees, and its main component is cinnamaldehyde. Cinnamon oil has been used to maintain food quality and extend shelf life. Studies have shown that cinnamon oil inhibits the growth of various bacteria and minimizes the loss of soluble dry matter in food. In addition, cinnamon oil has a positive effect on the metabolic process of antioxidants during food preservation. Its components reduce the content of reactive oxygen species, prevent the loss of certain low molecular weight antioxidants in fruits, and help enhance antioxidant activity during storage. This helps to keep the fruit in optimal condition throughout the storage period. However, the pungent smell and high volatility of cinnamon oil limit its application. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention aims to provide a biodegradable food preservative film, the obtained film is biodegradable, has antibacterial and antioxidant activities, and has good ductility and flexibility, can be used as a food preservative film, and can be used repeatedly. The problems of high volatility and instability of cinnamon oil are solved.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A biodegradable food preservative film is characterized in that the preservative film is a chitosan and polyvinyl alcohol composite film loaded with cinnamon oil microcapsules, containing 0.3% to 0.6% of cinnamon oil microcapsules, 0.8% of chitosan, 2.4% of polyvinyl alcohol, 0.3% of glycerol, and the balance of distilled water.

[0008] Preferably, the components by weight are: 0.6% cinnamon oil microcapsules, 0.8% chitosan, 2.4% polyvinyl alcohol, 0.3% glycerol, and the rest is distilled water.

[0009] A method for preparing a biodegradable food preservative film comprises the following steps:

[0010] (1) mixing chitosan with 1% acetic acid solution to obtain a chitosan solution with a concentration of 2%;

[0011] (2) dissolving polyvinyl alcohol in distilled water at high temperature to obtain a polyvinyl alcohol solution with a concentration of 4%;

[0012] (3) mixing the polyvinyl alcohol solution, the chitosan solution and glycerol in a ratio of 9:3:1 to obtain a mixed solution;

[0013] (4) Add cinnamon oil to β-cyclodextrin to form a microcapsule emulsion, filter and wash the precipitate to obtain microcapsules. Add the microcapsules to the mixed solution, stir evenly, ultrasonically degas and let stand to obtain a film-forming solution, the concentration of cinnamon oil microcapsules is 0.3% to 0.6%;

[0014] (5) Pour the film-forming liquid into a mold to form a film, let it stand and heat to obtain a composite antibacterial film, remove the film, and use it after balancing at a relative humidity of 75% and room temperature for 24 hours.

[0015] The invention discloses an application of a biodegradable food preservative film in inhibiting the growth of bacterial biofilms, wherein the bacteria are gram-negative bacteria Escherichia coli or gram-positive bacteria Staphylococcus aureus.

[0016] The beneficial effects of the present invention are:

[0017] (1) In the present invention, cinnamon oil microcapsules are added to a mixed solution of chitosan, polyvinyl alcohol and glycerol to prepare a film with a tear strength of 21.18 to 43.21 N / mm 2, elongation at break is 82.60% to 147.56%, antioxidant activity is 27.47% to 36.87%. It can be used as food preservative film and can be used repeatedly.

[0018] (2) The chitosan and polyvinyl alcohol composite film loaded with cinnamon oil microcapsules obtained by the present invention has a good inhibitory effect on Escherichia coli and Staphylococcus aureus.

[0019] (3) The cinnamon oil is made into microcapsules and added into biodegradable films to alleviate the volatilization of plant essential oils and improve the antibacterial and antioxidant activities of chitosan and polyvinyl alcohol composite films. The preparation method is simple and takes a short time to make. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The antibacterial activity of cinnamon oil capsule films of different concentrations against Escherichia coli and Staphylococcus aureus is shown in the antibacterial activity result diagram of samples 1-4 obtained in Example 1;

[0021] Figure 2 The antioxidant activity of cinnamon oil capsule films of different concentrations is the antioxidant activity result diagram of samples 1-4 obtained in Example 1;

[0022] Figure 3 The appearance of bananas preserved by cinnamon oil capsule films of different concentrations is the banana preservation result diagram of samples 1-4 obtained in Example 1. DETAILED DESCRIPTION

[0023] In order to make the purpose and technical solution of the present invention clearer, the following specific examples are used to explain in detail, but are not limited to these specific examples. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0024] Example 1 Sample preparation

[0025] It should be noted that in the following examples, the accession number of Staphylococcus aureus is ATCC 6538, and the accession number of Escherichia coli is ATCC 8739, and the source is China General Microbiological Culture Collection Administration Center.

[0026] 1. Preparation of cinnamon oil microcapsules

[0027] First, 6 g of β-cyclodextrin was dissolved in 100 ml of distilled water to form a saturated solution. The dissolution process was carried out at 60 °C with continuous magnetic stirring for 20 min. After complete dissolution, 1 mL of cinnamon oil dissolved in 10 mL of ethanol was added, and the mixture was stirred at 450 rpm for 2.5 hours to form a microcapsule emulsion. The emulsion was then stored in a refrigerator at 4 °C overnight. The next day, the solution was filtered to collect the precipitate and washed with anhydrous ethanol. The resulting solid was dried to constant weight to obtain cinnamon oil microcapsules. Finally, the dried powder was stored in a dry container for future use.

[0028] 2. Experiment on the effect of cinnamon oil microcapsules of different qualities on antibacterial activity

[0029] First, a 2% chitosan solution was prepared by dispersing chitosan in an acetic acid solution at 60°C until uniform. At the same time, polyvinyl alcohol was dissolved in distilled water and heated at 95°C to obtain a 4% polyvinyl alcohol solution. Then polyvinyl alcohol, chitosan and glycerol solution were mixed in a fixed ratio of 9:3:1. The mixture was stirred at 25°C for 6 hours to ensure uniform distribution. Subsequently, different masses of cinnamon oil microcapsules (0.09g, 0.18g, 0.27g) were added and stirred for 1 hour to ensure uniform dispersion of the cinnamon oil microcapsules. The mixed membrane solution was then ultrasonically degassed. 30 grams of the membrane-forming solution was equally poured into a 10 cm × 10 cm culture dish, placed in a desiccator at 23°C to form a thin film, taken out for demolding, and used after equilibration at 75% relative humidity and room temperature for 24 hours. The results are shown in Tables 1 and 2.

[0030] Table 1 Composition of different samples

[0031]

[0032] Example 2 Sample performance test

[0033] The performance tests of the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules prepared by samples 1-4 of the present invention were carried out as follows:

[0034] 1. Mechanical properties test

[0035] The thickness of the sample was measured using a digital micrometer. Five points were randomly selected from the film sample to be tested and the average was taken. The mechanical properties of the sample were measured using an electric peel force tester. The film sample was cut into 10 mm × 60 mm, the initial distance was set to 40 mm, and stretched at a speed of 5 mm / min until it broke. The tear strength (N / mm 2 ) and elongation at break (%). The results are shown in Table 2:

[0036] Table 2 Effects of different concentrations of cinnamon oil microcapsules on the mechanical properties of films

[0037]

[0038] The results show that: Samples 1-4 show that as the concentration of cinnamon oil microcapsules increases, the tear strength of the prepared chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules increases, but the elongation at break decreases.

[0039] 2. Antibacterial activity test

[0040] The present invention uses a paper diffusion method to judge the inhibitory effect of chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules on gram-negative bacteria (Escherichia coli) and gram-positive bacteria (Staphylococcus aureus): the film sample is cut into a disc with a diameter of 6 mm, and both sides of the disc are sterilized under ultraviolet light for 30 minutes before use. A single bacterial colony is inoculated in 5 ml LB liquid culture medium, 37 ° C, 180 rpm, and after inoculation for 12 hours, 50 μL of bacterial solution is diluted with 4950 μL fresh LB liquid culture medium, and cultured for 3 hours at 37 ° C, 180 rpm until OD600 reaches 0.5 to obtain a bacterial inoculum. 100 μL of bacterial suspension is evenly coated on a solid culture medium plate, and the disc is attached to the surface of the culture medium with sterile tweezers, and the diameter of the inhibition zone is measured after 24 hours.

[0041] like Figure 1 As shown, the results show that the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules prepared by samples 1-4 have antibacterial activity against Staphylococcus aureus and Escherichia coli. As the concentration of cinnamon oil microcapsules increases, the antibacterial activity of the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules is stronger.

[0042] 3. Antioxidant Activity Test

[0043] Dissolve 100 mg of membrane sample in 2 mL of deionized water and keep at 25°C for 24 h to obtain the membrane extract. Mix the membrane extract with ABTS test reagent and react at room temperature in the dark for 6 min. Measure the absorbance at a wavelength of 414 nm and record it as A. sample Mix equal amounts of deionized water and ABTS test reagent, and measure the absorbance at a wavelength of 414 nm, which is recorded as A control . Calculate the ABTS free radical scavenging rate according to the formula:

[0044]

[0045] like Figure 2 As shown, the results show that the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules prepared by samples 4-6 of the present invention have good antioxidant activity. As the concentration of cinnamon oil microcapsules increases, the antioxidant activity of the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules is stronger.

[0046] 4. Food preservation test

[0047] Cut the peeled bananas into columns with a height of 2 cm and a diameter of 2 cm, and arrange them neatly in a polypropylene plastic box with a size of 10 cm × 10 cm × 6.2 cm. Each group contains three randomly assigned banana samples, divided into five groups. The first group of banana samples were placed in a polypropylene plastic box and covered with a polyethylene plastic wrap as a control group, the second group of banana samples were placed in a polypropylene plastic box and covered with the film prepared by sample 1, and the third, fourth and fifth groups were covered with the films prepared by samples 2, 3 and 4 on the polypropylene plastic boxes, respectively. Use each film sample with a size of 10cm × 10cm to cover the plastic box containing the banana samples. Then, they were stored at 25°C, and data were collected every 24 hours. As Figure 3 As shown, the results show that the chitosan and polyvinyl alcohol composite films loaded with cinnamon oil microcapsules prepared by samples 4-6 of the present invention can effectively alleviate the browning of bananas, thereby extending the shelf life of bananas. The higher the concentration of cinnamon oil microcapsules, the better the preservation effect.

[0048] The above are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Under the technical concept of the present invention, those skilled in the art can understand that equivalent structural changes made using the contents of the present invention's specification and drawings, or direct / indirect application in other related technical fields are all included in the patent protection scope of the present invention.

Claims

1. A biodegradable food preservative film, characterized in that: The fresh-keeping film is a composite film of chitosan and polyvinyl alcohol loaded with cinnamon oil microcapsules, and the tear strength of the composite film is 21.18-43.21N / mm 2 The elongation at break was 82.60% to 147.56%, and the antioxidant activity was 27.47% to 36.87%.

2. A biodegradable food preservative film according to claim 1, characterized in that: The fresh-keeping film comprises the following raw materials by weight percentage: 0.3% to 0.6% of cinnamon oil microcapsules; 0.8% of chitosan; 2.4% of polyvinyl alcohol; 0.3% of glycerol; and the balance is distilled water.

3. The biodegradable food preservative film according to claim 1, characterized in that: The fresh-keeping film comprises the following raw materials by weight percentage: 0.6% of cinnamon oil microcapsules, 0.8% of chitosan, 2.4% of polyvinyl alcohol and 0.3% of glycerol.

4. The method for preparing a biodegradable food preservative film according to any one of claims 1 to 3, characterized in that: The steps include: (1) mixing chitosan with 1% acetic acid solution to obtain a chitosan solution with a concentration of 2%; (2) dissolving polyvinyl alcohol in distilled water at high temperature to obtain a polyvinyl alcohol solution with a concentration of 4%; (3) mixing the polyvinyl alcohol solution, the chitosan solution and glycerol in a ratio of 9:3:1 to obtain a mixed solution; (4) adding cinnamon oil to β-cyclodextrin to form a microcapsule emulsion, filtering, washing and precipitating to obtain microcapsules; adding the microcapsules to the mixed solution, stirring evenly, ultrasonically degassing and standing to obtain a film-forming solution, wherein the concentration of cinnamon oil microcapsules is 0.3% to 0.6%; (5) Pour the film-forming liquid into a mold to form a film, let it stand and heat to obtain a composite antibacterial film, remove the film, and use it after balancing at a relative humidity of 75% and room temperature for 24 hours.

5. The biodegradable food preservative film according to claim 3, characterized in that: The optimum concentration of the cinnamon oil microcapsules is 0.6%.

6. Use of the biodegradable food preservative film according to claim 1 in antibacterial and fresh-keeping.

7. The use according to claim 6, characterized in that: The bacteria are Escherichia coli or Staphylococcus aureus.

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