Chitosan / polyvinyl alcohol antioxidant composite film based on divaricate saposhnikovia root extract as well as preparation method and fresh-keeping application of chitosan / polyvinyl alcohol antioxidant composite film

Abstract

The invention discloses a chitosan / polyvinyl alcohol antioxidant composite film based on a divaricate saposhnikovia root extract and a preparation method and fresh-keeping application thereof, and relates to the chitosan / polyvinyl alcohol antioxidant composite film based on the divaricate saposhnikovia root extract and the preparation method and fresh-keeping application thereof. The invention aims to solve the problems that the plastic packaging film is difficult to degrade, the traditional chemical preservative affects the food quality and harms the body health, and the like, and widens the windproof application range. The experimental method comprises the following steps: by taking radix saposhnikoviae as a raw material, extracting radix saposhnikoviae chromone by adopting a deep eutectic solvent, purifying by using AB-8 type macroporous resin, and preparing the composite film by matching the obtained purified product with chitosan, polyvinyl alcohol and glycerol. The method is simple and easy to operate, the divaricate saposhnikovia root is used for developing the composite film, the added value of the divaricate saposhnikovia root can be increased, and compared with an existing composite film, the used raw materials are natural substances extracted from the divaricate saposhnikovia root, so that the method is safer and more reliable, higher in oxidation resistance and better in preservation effect.

Description

Technical Field

[0001] The invention relates to a chitosan / polyvinyl alcohol antioxidant composite film based on fangfeng extract, a preparation method thereof and a fresh-keeping application thereof. Background Art

[0002] At present, the food packaging widely circulated on the market is plastic packaging, and its raw materials mainly include polyethylene, polypropylene and polyethylene terephthalate. The problem of "white pollution" caused by plastic packaging is becoming more and more serious. With the gradual increase of people's environmental awareness, degradable packaging film is considered to be a substitute for traditional plastics. Therefore, seeking degradable packaging film substrates has become a research hotspot in recent years. Polyvinyl alcohol (PVA) is a water-soluble polymer with many unique properties. It has excellent biodegradability, which makes it occupy a unique and very important position in film materials. At present, chitosan is the second largest sugar source after cellulose, which comes from shrimp and crab shells. Due to its excellent biocompatibility, renewability and degradability, chitosan is considered to be a safe food preservative material. However, the poor antioxidant activity of chitosan limits the application of chitosan in food preservation. Therefore, improving the antioxidant property of cling film so that it has excellent preservation effect has become an urgent problem to be solved in its promotion and application.

[0003] In order to slow down the oxidation rate of fruits and vegetables, chemical preservatives and other methods are usually used to extend the shelf life of fruits and vegetables. However, some chemical preservatives may contain harmful chemicals, which may leave cleaning residues or penetrate into the fruits and vegetables. Long-term consumption of fruits and vegetables with chemical residues on the surface has certain potential toxicity to the human body. At the same time, the use of chemical agents has a certain degree of damage to the ecological environment. Plant-based preservatives represented by Chinese herbal medicines have attracted the attention of a large number of researchers. Finding a relatively safe and effective preservative with no side effects on the human body from natural plants has become a hot topic in the food industry. Fangfeng, a plant of the genus Fangfeng in the Umbelliferae family, is spicy, slightly sweet, and warm in nature. It has the effects of dispelling wind, dispelling wind and stopping spasms, and relieving dampness and pain. At present, Fangfeng is often used in the form of compound prescriptions, such as Yupingfeng Powder, Guben Fangxiao Drink, Fangfeng Decoction, etc., as well as the listed Chinese patent medicines Fangfeng Tongsheng Pills and Xinqin Granules. However, the application research of Fangfeng extracts in preservation at home and abroad is basically blank, which not only causes a waste of resources, but also greatly restricts the research, development and application of Fangfeng. The main chemical components of Saposhnikovia divaricata include chromones, coumarins, volatile oils, polysaccharides, etc. Among them, chromones are the main active ingredients of Saposhnikovia divaricata, which have excellent antioxidant properties, can effectively remove free radicals, and protect cells from oxidative damage. Especially in situations where natural ingredients are needed, they can be used as antioxidants. For example, in the disclosed invention patent "A preparation method of a wide-lipped Alpinia galanga extract and its application in fruit preservation" (authorization announcement number: CN115812777B), a preparation method of a wide-lipped Alpinia galanga extract and its application in fruit preservation are disclosed. In this method, ethanol is used to extract the active ingredients in the wide-lipped Alpinia galanga, but the use of organic solvents has problems such as high cost and high toxicity.

[0004] The present invention provides a chitosan / polyvinyl alcohol antioxidant composite film based on fangfeng extract, and a preparation method and preservation application thereof. By adopting biodegradable polyvinyl alcohol and chitosan as the matrix of the film, the problems such as environmental pollution caused by traditional films are overcome; the fangfeng extract as an antioxidant can effectively enhance the antioxidant function of the film, and the film material finally obtained has potential application in the field of degradable fresh-keeping antioxidant packaging films. Summary of the invention

[0005] In order to solve the current problems of traditional film pollution and potential health risks of traditional chemical preservatives, the present invention provides a biodegradable and easy-to-make chitosan / polyvinyl alcohol antioxidant composite film based on fangfeng extract, as well as its preparation method and preservation application.

[0006] A method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on a siler extract is specifically carried out according to the following steps:

[0007] 1. Preparation of fangfeng extract: washing fangfeng with distilled water to remove dust and impurities, drying in an oven set at a temperature of 55-65°C for 23-25h, crushing the dried fangfeng in a grinder, and passing through a 40-80 mesh sieve to obtain fangfeng powder; mixing the obtained fangfeng powder and a low eutectic solvent composed of betaine as a hydrogen bond acceptor and glycerol as a hydrogen bond donor at a solid-liquid ratio of 1:30-50, the molar ratio of betaine to glycerol is 1:3-5, and the water content of the low eutectic solvent is 20-40%; after the mixing is completed, the ultrasonic time is set to 25-35min, the ultrasonic power is set to 310-330W, and the temperature is set to 50-60°C; after the ultrasonication, the mixture is diluted 3 times and filtered, and the liquid part obtained by filtration is purified by AB-8 macroporous resin, and the purified product is freeze-dried to obtain the fangfeng extract;

[0008] 2. Preparation of film-forming solution: Mix chitosan with 0.5-1.5% acetic acid solution at 80-100°C and heat and stir for 1.5-2.5h to prepare a chitosan solution with a mass fraction of 1.5-2.5%; dissolve polyvinyl alcohol in deionized water and heat and stir for 0.5-1.5h at 80-100°C to prepare a polyvinyl alcohol solution with a mass fraction of 1.5-2.5%; mix the polyvinyl alcohol solution with the chitosan solution at a ratio of 1:3- 5, and heated and stirred at 50-70°C for 0.5h; glycerol was added, and heated and stirred at 50-70°C for 0.5h to obtain a film-forming solution, wherein the mass ratio of the glycerol added to chitosan was 0.1-0.3:1; the fangfeng extract was added to the film-forming solution, and heated and stirred at 50-70°C for 0.5h to obtain a film-forming solution loaded with the fangfeng extract, wherein the mass ratio of the fangfeng extract to chitosan was 0.05-0.2:1;

[0009] 3. Preparation of plastic wrap: The obtained film-forming solution loaded with fangfeng extract is ultrasonically treated at an ultrasonic power of 290-310 W and an ultrasonic time of 25-35 min, and then the bubbles in the film-forming solution are removed. The film-forming solution is cast in a mold and dried at 50-70°C for 12 h to obtain a plastic wrap.

[0010] An application of an antioxidant chitosan / polyvinyl alcohol composite film based on a fangfeng extract is specifically carried out according to the following steps:

[0011] 1. Study on the effect of composite film on the physical changes of fresh strawberries: Fresh strawberries of uniform size, color and maturity, and without mechanical damage and pests and diseases were grouped. After absorbing the surface moisture with absorbent paper, the strawberries not coated with composite film were used as the blank control group, and the strawberries coated with composite film were used as the experimental group. Each group of strawberries was photographed every day to observe the changes in the strawberries.

[0012] 2. Study on the effect of composite film on weight loss of fresh strawberries: Fresh strawberries of uniform size, uniform color and maturity, and without mechanical damage and pests and diseases were grouped. After absorbing surface moisture with absorbent paper, the strawberries not coated with composite film were used as blank control group, and the strawberries coated with composite film were used as experimental group. Each group of strawberries was weighed every day, and the weight loss rate was calculated according to the formula weight loss rate / %=(G1-G2) / G1×100; where: G1 is the mass before storage, g; G2 is the mass after storage, g.

[0013] The advantages of the present invention are as follows: (1) All materials used are biodegradable and environmentally friendly, which reduces the pollution of the plastic wrap to the environment. (2) It has good antioxidant function, can effectively reduce the loss of water on the surface of fruits and vegetables, and maintain a high nutritional content of fruits and vegetables. (3) The preparation method of the present invention is simple to operate, solves the problems of high degradation rate of plastic wrap, safety and environmental protection, and provides a new way for the development of windproof products, which has a wide range of uses and high economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a physical picture of the composite film and a cross-sectional SEM image. Figure 1 It can be seen that as the concentration of the Saposhnikovia extract gradually increases, the color of the film gradually darkens, which is due to the color of the Saposhnikovia extract itself. From the cross-sectional image of the film, it can be seen that when the mass ratio of chitosan to Saposhnikovia extract is 1:0.05-0.15, the cross-sectional image is compact and continuous, indicating that chitosan, polyvinyl alcohol and Saposhnikovia extract have good compatibility. However, when the mass ratio of chitosan to Saposhnikovia extract is 1:0.2, obvious wrinkles and a small amount of particles are observed, which may be due to the presence of more insoluble substances in the Saposhnikovia extract at a higher concentration;

[0015] Figure 2 is the ultraviolet transmittance spectra of the fresh-keeping films prepared in Examples 2, 3, 4, 5 and Comparative Example 1, from Figure 2 It can be seen that the comparative example 1, i.e., pure chitosan / polyvinyl alcohol film, exhibits high transparency in the visible light wavelength range, but it is insufficient in terms of UV blocking ability. However, the addition of the Saposhnikovia extract significantly enhanced the UV resistance of the film. The UV transmittance of all composite films between 200 and 400 nm was significantly reduced. Therefore, it is clear that the Saposhnikovia extract has great potential in expanding the functional application of chitosan / polyvinyl alcohol antioxidant films;

[0016] Figure 3 1,1-diphenyl-2-trinitrophenylhydrazine free radical (DPPH free radical) scavenging rate diagram of the cling film prepared in Examples 2, 3, 4, 5 and Comparative Example 1, from Figure 3It can be seen that all films showed antioxidant activity in scavenging free radicals. For Comparative Example 1, i.e., pure chitosan / polyvinyl alcohol film, the amino and hydroxyl groups of chitosan itself have the ability to capture free radicals and have certain antioxidant properties. After adding the antioxidant Saposhnikovia extract, the DPPH free radical scavenging ability of the composite film was significantly enhanced, and gradually increased with the increase of the extract content;

[0017] Figure 4 This is a graph showing the changes of the actual strawberry with composite film applied over the storage time. Figure 4 It can be seen that the blank control group showed slight dehydration and rot on the third day, while the film had no obvious effect on the freshness of the strawberries, only slight dehydration occurred, causing the fruit surface to lose its bright luster. The limited freshness period of the strawberries in the blank control group was 3 days, and the effective shelf life of the strawberries in comparative example 1, i.e., pure chitosan / polyvinyl alcohol film, was 5 days. The introduction of the windproof extract film greatly extended the freshness period of the strawberries, and the shelf life of the strawberries was extended to 9 days, indicating that during the long-term storage process, the strawberries did not undergo large-scale deterioration, and the composite film could effectively prevent the fruit from rotting and oxidation;

[0018] Figure 5 This is a graph showing the weight loss rate of strawberries after composite film application versus storage time. Figure 5 It can be seen that compared with the blank control group, the weight loss rate of composite film strawberries has the same trend, and the weight loss rate is lower than that of the blank control group. The loss of fruit moisture will cause the weight of the fruit to decrease during storage. The barrier ability of plastic wrap to water vapor and oxygen can significantly reduce the weight loss rate of fruit, thereby extending the shelf life of fruit. The results show that the composite film can effectively prevent the evaporation of fruit moisture and maintain the texture of the fruit; DETAILED DESCRIPTION

[0019] Embodiment 1:

[0020] The present embodiment is a method for preparing a siler extract, which is specifically completed by the following steps:

[0021] The fangfeng was washed with distilled water to remove dust and impurities, dried in an oven at 60°C for 24 hours, and the dried fangfeng was crushed in a pulverizer and passed through a 60-mesh sieve to obtain fangfeng powder. The fangfeng powder obtained was mixed with a low eutectic solvent composed of betaine as a hydrogen bond acceptor and glycerol as a hydrogen bond donor at a solid-liquid ratio of 1:38, the molar ratio of betaine to glycerol was 1:4, and the water content of the low eutectic solvent was 29%; after the mixing was completed, the ultrasonic time was set to 30 minutes, the ultrasonic power was set to 320W, and the temperature was set to 54°C; after the ultrasonication, the mixture was diluted 3 times and filtered, and the liquid part obtained by filtration was purified by AB-8 macroporous resin, and the purified product was freeze-dried to obtain the fangfeng extract.

[0022] The fangfeng extracts used in the following embodiments were all prepared by the method of Example 1.

[0023] Embodiment 2:

[0024] The present embodiment is a method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on a siler extract, which is specifically completed by the following steps:

[0025] 1. Mix chitosan with 1% acetic acid solution by mass, heat and stir at 90°C for 2h to prepare a chitosan solution with a mass fraction of 2%; dissolve polyvinyl alcohol in deionized water, heat and stir at 90°C for 1h to prepare a polyvinyl alcohol solution with a mass fraction of 2%; mix the polyvinyl alcohol solution with the chitosan solution in a ratio of 1:4 and heat and stir at 60°C for 0.5h; add glycerol, heat and stir at 60°C for 0.5h to obtain a film-forming solution, wherein the mass ratio of the glycerol added to the chitosan is 0.2:1; add the fangfeng extract to the film-forming solution, heat and stir at 60°C for 0.5h to obtain a film-forming solution loaded with the fangfeng extract, wherein the mass ratio of the fangfeng extract to chitosan is 0.05:1;

[0026] 2. Preparation of cling film: The obtained film-forming solution was subjected to ultrasonic treatment at an ultrasonic power of 300 W for 30 min, and then bubbles in the film-forming solution were removed. The film-forming solution was cast into a mold and dried at 60° C. for 12 h to obtain the cling film.

[0027] Embodiment 3:

[0028] Compared with Example 2, the difference is that in step 1, the mass ratio of chitosan to fangfeng extract is 1:0.1.

[0029] Embodiment 4:

[0030] Compared with Example 2, the difference is that in step 1, the mass ratio of chitosan to fangfeng extract is 1:0.15.

[0031] Embodiment 5:

[0032] Compared with Example 2, the difference is that in step 1, the mass ratio of chitosan to fangfeng extract is 1:0.2.

[0033] Comparative Example 1:

[0034] Compared with Example 2, the difference is that in step 1, no fangfeng extract is added.

[0035] A preservation application of chitosan / polyvinyl alcohol antioxidant composite film based on fangfeng extract is specifically carried out according to the following steps:

[0036] 1. Study on the effect of composite film on the physical changes of fresh strawberries: Fresh strawberries of uniform size, color and maturity, and without mechanical damage and pests and diseases were grouped. After absorbing the surface moisture with absorbent paper, the strawberries not coated with composite film were used as the blank control group, and the strawberries coated with composite film were used as the experimental group. Each group of strawberries was photographed every day to observe the changes in the strawberries.

[0037] 2. Study on the effect of composite film on weight loss of fresh strawberries: Fresh strawberries of uniform size, color and maturity, and without mechanical damage and pests and diseases were grouped. After absorbing surface moisture with absorbent paper, the strawberries not coated with composite film were used as blank control group, and the strawberries coated with composite film were used as experimental group. Each group of strawberries was weighed every day, and the weight loss rate was calculated according to the formula: weight loss rate / % = (G1-G2) / G1×100%; where: G1 is the mass before storage, g; G2 is the mass after storage, g.

Claims

1. A method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on a siler extract, which is specifically carried out according to the following steps:

1. Preparation of the extract of Saposhnikovia divaricata: washing the Saposhnikovia divaricata with distilled water to remove dust and impurities, drying in an oven set at a temperature of 55-65°C for 23-25 ​​h, crushing the dried Saposhnikovia divaricata in a grinder, and sieving through a 40-80 mesh sieve to obtain Saposhnikovia divaricata powder; mixing the obtained Saposhnikovia divaricata powder with a low eutectic solvent; after the mixing is completed, the ultrasonic time is set to 25-35 min, the ultrasonic power is set to 310-330 W, and the temperature is set to 50-60°C; after the ultrasonic treatment is completed, the mixture is diluted 3 times and filtered, and the liquid part obtained by filtration is purified by AB-8 macroporous resin, and the purified product is freeze-dried to obtain the Saposhnikovia divaricata extract; 2. Preparation of film-forming solution: chitosan and acetic acid solution are mixed and heated and stirred at 80-100°C for 1.5-2.5 h to prepare chitosan solution; polyvinyl alcohol is dissolved in deionized water and heated and stirred at 80-100°C for 0.5-1.5 h to prepare polyvinyl alcohol solution; polyvinyl alcohol solution and chitosan solution are mixed in a ratio of 1:3-5 and heated and stirred at 50-70°C for 0.5 h; glycerol is added and heated and stirred at 50-70°C for 0.5 h to obtain a film-forming solution; the fangfeng extract is added to the film-forming solution and heated and stirred at 50-70°C for 0.5 h to obtain a film-forming solution loaded with the fangfeng extract; 3. Preparation of plastic wrap: The obtained film-forming solution loaded with fangfeng extract is subjected to ultrasonic treatment at an ultrasonic power of 290-310 W and an ultrasonic time of 25-35 min, and then the bubbles in the film-forming solution are removed. The film-forming solution is cast in a mold and dried at 50-70 ℃ for 12 h to obtain a plastic wrap.

2. The method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on siler extract according to claim 1, characterized in that: In step 1, the composition of the low eutectic solvent is that betaine is a hydrogen bond acceptor, glycerol is a hydrogen bond donor, the molar ratio of betaine to glycerol is 1:3-5, and the water content of the low eutectic solvent is 20-40%.

3. The method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on siler extract according to claim 1, characterized in that: In step 1, the windproof powder and the low eutectic solvent are mixed at a solid-to-liquid ratio of 1:30 to 50.

4. The method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on siler extract according to claim 1, characterized in that: In step 2, chitosan is mixed with 0.5-1.5% acetic acid solution by mass and heated to prepare a chitosan solution; the mass concentration of chitosan in the chitosan solution is 1.5-2.5%.

5. The method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on siler extract according to claim 1, characterized in that: The mass concentration of polyvinyl alcohol in the polyvinyl alcohol solution in step 2 is 1.5-2.5%.

6. The method for preparing a chitosan / polyvinyl alcohol antioxidant composite film based on siler extract according to claim 1, characterized in that: In step 2, the mass ratio of chitosan to glycerol in the film-forming solution is 1:0.1-0.3, and the mass ratio of chitosan to the siler extract in the film-forming solution is 1:0.05-0.

2.

7. Application of a chitosan / polyvinyl alcohol antioxidant composite film based on fangfeng extract prepared by the preparation method of claim 1, characterized in that It is done in the following steps:

1. Study on the changes of fresh strawberries under the influence of composite film: fresh strawberries of uniform size, color and maturity, and without mechanical damage and pests and diseases were grouped. After absorbing the surface moisture with absorbent paper, the strawberries not coated with composite film were used as the blank control group, and the strawberries coated with composite film were used as the experimental group. The strawberries in each group were photographed every day to observe the changes of the strawberries.

2. Study on the effect of composite film on weight loss of fresh strawberries: Fresh strawberries of uniform size, color and maturity, without mechanical damage and pests and diseases were grouped. After absorbing surface moisture with absorbent paper, the strawberries not coated with composite film were used as blank control group, and the strawberries coated with composite film were used as experimental group. Each group of strawberries was weighed every day, and the weight loss rate was calculated according to the formula: weight loss rate / % = (G1-G2) / G1×100%; where: G1 is the mass before storage, g; G2 is the mass after storage, g.

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