Preparation method and application of chlorine dioxide preservative paper

Abstract

The invention discloses a preparation method and application of chlorine dioxide preservative paper.The preparation method comprises the steps that starch, nanocellulose, hydrogen peroxide, ferric sulfate, distilled water and sodium hydroxide are mixed to obtain gelatinized starch, and then the gelatinized starch is mixed with water-based acrylic resin, casein, alkyl glycoside and ammonium persulfate to obtain composite starch glue; mixing sodium chlorite and composite starch glue to obtain fresh-keeping coating liquid A, and then coating the fresh-keeping coating liquid A on fresh-keeping base paper to obtain fresh-keeping coating liquid A paper; citric acid and distilled water are mixed to obtain fresh-keeping coating liquid B, and then fresh-keeping base paper is soaked in the fresh-keeping coating liquid B to obtain fresh-keeping coating liquid B paper; the fresh-keeping coating liquid A paper and the fresh-keeping coating liquid B paper are attached to obtain the chlorine dioxide fresh-keeping paper. The chlorine dioxide fresh-keeping paste is pasted on the inner side of the blueberry packaging box cover to keep the blueberries fresh. The chlorine dioxide preservative paper prepared by the invention can solve the problems of burst release and short retention time of chlorine dioxide, can reduce the problems of easy softening, rot and deterioration of picked blueberries, prolongs the shelf life of the blueberries, and improves the commodity value of the blueberries.

Description

Technical Field

[0001] The invention relates to the technical field of fruit and vegetable preservation, and in particular to a preparation method of chlorine dioxide fresh-keeping paper and application thereof. Background Art

[0002] Blueberry (Vaccinium spp.) is a perennial shrub, mainly produced in Northeast my country. Blueberry is popular all over the world for its delicious taste and nutritional value. Blueberries are harvested in the hot and rainy summer. After harvesting, they still respire, but without the supply of nutrients and water, they need to rely on their own metabolism. The nutrients in the fruit are consumed and gradually reduced, and the antioxidant substances and physiological metabolic activities of ripening also change accordingly. The fruit matures and ages, and the quality deteriorates.

[0003] With the booming development of the Internet economy, various fresh food e-commerce companies have emerged. Blueberries, as a high-value, high-end specialty fruit, are the new favorite of fresh food e-commerce. Fresh blueberries are easily rotten due to their high water content and thin skin. During the long transportation and storage process after picking, they are easily scratched by mechanical impact, resulting in water loss and microbial infection, which makes the blueberries easy to soften, rot and deteriorate, causing them to lose their commodity value during the post-harvest storage period, seriously restricting the development of the blueberry industry.

[0004] The main methods for preserving blueberries after harvest include physical preservation methods such as low-temperature refrigeration and controlled atmosphere preservation, as well as chemical preservation methods such as spraying and soaking with chemical preservatives. However, low-temperature refrigeration and controlled atmosphere preservation have high energy consumption and high costs, and are limited in production and transportation. Spraying and soaking with chemical preservatives to preserve fruits and vegetables is inconvenient for large-scale fruit processing, resulting in uneven preservation and easily causing preservatives to remain on the surface of blueberries, affecting their quality and food safety.

[0005] Chlorine dioxide (ClO2) has strong oxidizing properties and bactericidal effects. Since the mid-20th century, ClO2 has been used as an antibacterial agent and has been rated as a Class A1 safe disinfectant by the World Health Organization. ClO2 can destroy tyrosine on proteins in bacteria, denature proteins in bacteria, and cause bacterial death. Due to its high oxidizing ability and biocidal activity, ClO2 is considered a low-cost, easy-to-use, and efficient disinfectant. Although ClO2 can effectively kill microorganisms such as bacteria and viruses, it has no toxic effects on animals, plants, and human bodies. Gaseous ClO2 is a stronger oxidant than chlorine and liquid ClO2, up to 2.5 times and 5 times, respectively. Due to its small molecular size (about 0.124nm), ClO2 gas can enter the small gaps of fresh fruits and vegetables, come into contact with bacteria hidden in fruits and vegetables, destroy their cell membranes and enzymes, and thus inactivate the bacteria. At the same time, ClO2 gas has good adsorption and permeability to plant cell walls, which can prevent fruits and vegetables from generating ethylene and remove the generated ethylene, thereby delaying the aging and decay rate of fruits and vegetables, and playing a role in preserving fruits and vegetables. During the storage of fruits and vegetables, the slowly released ClO2 gas can close the stomata of fruits and vegetables, reduce the release of water, ethylene and ethanol, and can quickly and effectively prevent the corresponding metabolism of fruits and vegetables, remove substances such as ethylene and ethanol, and kill bacteria, playing a role in preserving fruits and vegetables.

[0006] ClO2 is an efficient and safe disinfectant and sterilizer that is currently used in all walks of life. However, ClO2 gas is unstable and easily decomposed by light, and ClO2 solution is volatile. It is generally inconvenient to make a concentrated solution, which reduces the convenience of using ClO2. Although ClO2 can be prepared into solid preparations such as tablets and granules, its stability is not good, making it inconvenient to use as a fruit and vegetable preservative and the effect is not good.

[0007] Chlorine dioxide cling paper is a slow-release preservation technology that does not come into direct contact with the product, is convenient and controllable, green and safe, and can preserve fruits and vegetables. It is currently widely used in fruit and vegetable preservation. Chlorine dioxide cling paper is made by laminating a paper base containing a chlorine dioxide precursor such as sodium chlorite and a paper base containing a weak acid together, and using a chemical reaction between sodium chlorite and the hydrogen ions in the weak acid to produce chlorine dioxide, which has stronger oxidizing and bactericidal abilities. However, chlorine dioxide cling paper is prone to explosive release of chlorine dioxide and a short retention time during preparation and use, resulting in poor chlorine dioxide preservation effects.

[0008] Therefore, solving the problems of explosive release and short retention time of chlorine dioxide in chlorine dioxide preservative paper and using chlorine dioxide preservative paper to preserve blueberries after harvest, thereby reducing the phenomenon of blueberries softening, rotting and deterioration after harvest and improving the quality of blueberries are technical issues that need to be urgently addressed in the blueberry post-harvest preservation industry. Summary of the invention

[0009] The object of the present invention is to provide a preparation method and application of chlorine dioxide fresh-keeping paper, so as to solve the problems of explosive release of chlorine dioxide in the chlorine dioxide fresh-keeping paper and short residence time proposed in the above background technology, and to preserve blueberries after harvesting by the chlorine dioxide fresh-keeping paper to reduce the blueberries from being easily softened, rotted and deteriorated after harvesting.

[0010] To achieve the above object, the present invention provides the following technical solution: a method for preparing chlorine dioxide cling film, which specifically comprises the following steps:

[0011] Step 1, preparation of gelatinized starch: weigh 60-65 parts by weight of distilled water and place it in a beaker, add 11-13 parts by weight of starch and 2-3 parts by weight of nanocellulose under 55-58°C water bath conditions, adjust the pH value to 10, add 0.4-0.5 parts by weight of hydrogen peroxide and 0.1-0.15 parts by weight of ferric sulfate, take out the beaker and place it in a magnetic stirrer at 60-62°C and 500-550r / min, stir for 25-28min, add 2.5-2.8 parts by weight of sodium hydroxide solution, and place it in a water bath at 60-62°C and stir for gelatinization for 25-28min to obtain gelatinized starch.

[0012] Step 2: Weigh 14-16 parts by weight of aqueous acrylic resin, 5-8 parts by weight of casein, and 0.8-1.2 parts by weight of alkyl glycoside, mix them evenly, place them in a plasma device for treatment for 180-210 seconds, place them in a beaker, add 255-260 parts by weight of distilled water, stir and mix, place them in a water bath at 60-62° C., add 0.07-0.08 parts by weight of ammonium persulfate, stir for 22-25 minutes, and obtain a mixed solution.

[0013] Step 3: Add the gelatinized starch obtained in step 1 to the mixed solution obtained in step 2, add polyethylene glycol when heated to 65-70° C., stir at a constant temperature for 20-25 minutes, adjust the pH value to 10, and obtain a composite starch glue.

[0014] Step 4: Place the composite starch glue obtained in step 3 in a water bath at 40-42° C., add 1.1-1.2 parts by weight of sodium chlorite, and stir for 4-5 minutes to mix evenly to obtain a fresh-keeping coating liquid A.

[0015] Step 5: Weigh 15-18 parts by weight of citric acid and dissolve it in 85-88 parts by weight of distilled water to prepare a fresh-keeping coating solution B.

[0016] Step 6: Apply the fresh-keeping coating liquid A evenly on the fresh-keeping base paper A twice, with an interval of 3 minutes between the two coatings and a coating amount of 330-340 g / m 2, place the coated fresh-keeping base paper A in a drying oven at 40-45°C for 8-10 minutes to obtain fresh-keeping coating liquid A paper, soak the fresh-keeping base paper B in the fresh-keeping coating liquid B for 60-70 seconds, take it out and place it in a drying oven at 40-45°C for 6-8 minutes to obtain fresh-keeping coating liquid B paper, and laminate the side of the fresh-keeping coating liquid A paper coated with the fresh-keeping coating liquid A with the fresh-keeping coating liquid B paper to obtain chlorine dioxide fresh-keeping paper.

[0017] The application of chlorine dioxide cling film in the preservation of blueberries is processed by the following method and steps:

[0018] S1. After picking blueberries, place them at 15-16℃ for 3.5-4 hours to dissipate the field heat, and select blueberries with uniform size, similar color, consistent maturity, no mechanical damage, and no pests or rot for preservation;

[0019] S2. Use a polyethylene terephthalate packaging box to package the blueberries treated in step S1, cut the chlorine dioxide fresh-keeping paper into the size of the blueberry packaging box lid and stick it on the inner side of the blueberry packaging box lid, stick the side of the fresh-keeping coating A paper that is not coated with the fresh-keeping coating A on the lid, and put the packaged blueberries into a foam box for transportation and storage.

[0020] As a preferred technical solution of the present invention, the starch is composed of wheat starch and corn starch in a mass ratio of 1.5 to 2:1.

[0021] As a preferred technical solution of the present invention, the nanocellulose particle size is 50 to 60 nm.

[0022] As a preferred technical solution of the present invention, the concentration of the sodium hydroxide solution is 30%.

[0023] As a preferred technical solution of the present invention, the charge density of the plasma equipment is 1200-1300C / cm 3 , gas flow rate is 1.5~1.6L / min, pressure is 100~105kPa, and temperature is 55~60℃.

[0024] As a preferred technical solution of the present invention, the fresh-keeping base paper A and the fresh-keeping base paper B are food-grade absorbent paper with a thickness of 0.5 to 0.8 mm, a length of 10 to 12 cm, and a width of 5 to 6 cm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention adds nanocellulose during the preparation process of chlorine dioxide fresh-keeping paper, and the nanocellulose interacts with starch molecules to form hydrogen bonds, so that more amylose and amylopectin molecules can seep out and dissolve in water, forming a more viscous colloidal solution, and enhancing the elasticity of starch gel. Nanoscale cellulose has a higher specific surface area and more hydroxyl groups, can form a stronger interaction with water molecules, can form a dense network structure, thereby preventing the loss of water, and improving the water holding capacity of starch gel. At the same time, nanocellulose can improve the flatness, smoothness and uniformity of the fresh-keeping coating on the fresh-keeping paper, thereby controlling the release rate and release amount of chlorine dioxide, achieving stable release of chlorine dioxide, reducing burst release, and thus better playing the fresh-keeping effect of chlorine dioxide.

[0027] 2. The present invention processes the aqueous acrylic resin, casein, and alkyl glycoside after mixing them uniformly in a plasma device. The aqueous acrylic resin has excellent adhesion and film-forming properties, and can be better attached to the fresh-keeping base paper after mixing with the fresh-keeping coating liquid, which helps chlorine dioxide to be evenly distributed and stably released on the fresh-keeping paper, thereby improving the fresh-keeping effect. Casein is a phosphorus-calcium binding protein, and contains hydrophilic groups and hydrophobic groups in the molecular structure. This structure can form hydrogen bonds or other interactions between casein and water molecules, enhance the binding force of casein and water molecules, and prevent water penetration at the same time, thereby maintaining the integrity and water resistance of the fresh-keeping coating liquid. Alkyl glycoside can improve the compatibility between each material, help the uniform dispersion and stable combination of each component in the fresh-keeping paper, and alkyl glycoside has strong antibacterial activity, can inhibit the growth and reproduction of microorganisms, thereby extending the fresh-keeping period of fruits and vegetables, and when making chlorine dioxide fresh-keeping paper, adding alkyl glycoside can further enhance the antibacterial ability of fresh-keeping paper and improve the fresh-keeping effect. The high-energy particles such as electrons and ions generated by the plasma equipment collide and react with the surfaces of water-based acrylic resin, casein, and alkyl glycoside, introducing new functional groups or chain segments, which can improve the wettability of the surface of the water-based acrylic resin, thereby improving its structure and functional properties, promoting the interaction and cross-linking reaction between the water-based acrylic resin and other materials, and enhancing the interaction between the materials, thereby promoting the stable release of chlorine dioxide and improving the preservation effect.

[0028] 3. Polyethylene glycol is a high molecular compound. Adding polyethylene glycol in the preparation process of chlorine dioxide cling paper can make the cling coating more evenly coated on the cling base paper, thereby improving the cling effect of the cling paper. Polyethylene glycol has hygroscopicity and water retention. It can adjust the moisture content in the coating layer to a certain extent, thereby affecting the release rate of chlorine dioxide and enhancing the preservation effect. At the same time, polyethylene glycol has excellent antistatic and antioxidant properties, which can maintain the release of chlorine dioxide and the stability of the cling paper.

[0029] 4. The present invention applies the prepared chlorine dioxide fresh-keeping paper to the storage and transportation of blueberries. From the perspective of logistics + packaging + preservatives, the blueberries after harvest are preserved, so that the storage, transportation and sales of blueberries are integrated, and the quality and commercial value of blueberries are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart for preparing chlorine dioxide cling paper;

[0031] Figure 2 It is a line graph of sodium chlorite retention rate of fresh-keeping coating A paper of the present invention;

[0032] Figure 3 A line graph showing the chlorine dioxide release amount of the chlorine dioxide cling paper of the present invention;

[0033] Figure 4 This is a line graph showing changes in hardness during storage of blueberries according to the present invention;

[0034] Figure 5 The bar graph of the decay rate change during the storage of blueberries of the present invention;

[0035] Figure 6 This is a bar graph showing the change in color difference L value during the storage of blueberries according to the present invention;

[0036] Figure 7 The bar graph of the change of soluble solids during the storage of blueberries of the present invention;

[0037] Figure 8 This is a line graph showing the changes in superoxide dismutase (SOD) during the storage of blueberries according to the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Chlorine dioxide fresh-keeping paper is a slow-release fresh-keeping technology that does not come into direct contact with the product, is convenient and controllable, green and environmentally friendly, and safe, and can preserve fruits and vegetables. Chlorine dioxide fresh-keeping paper is made by laminating a paper base containing a chlorine dioxide precursor such as sodium chlorite with a paper base containing a weak acid, and using a chemical reaction between sodium chlorite and the hydrogen ions in the weak acid to produce chlorine dioxide, which has stronger oxidizing and bactericidal abilities. When the fresh-keeping coating A paper containing sodium chlorite and the fresh-keeping coating B paper containing citric acid are laminated together, chlorine dioxide gas with a fresh-keeping effect will be produced. The reaction chemical formula is:

[0040] Nanocellulose is a nanoscale particle composed of cellulose molecules, mainly derived from natural plant cellulose such as wood, cotton, rice husks, and other plants. Nanocellulose interacts with starch molecules to form hydrogen bonds, which helps to destroy the structure of starch granules, allowing more amylose and amylopectin molecules to seep out and dissolve in water, enhancing the elasticity of starch gel and forming a more viscous colloidal solution. Nanocellulose has a higher specific surface area and more hydroxyl groups, which can form a stronger interaction with water molecules and form a dense network structure, thereby preventing water loss and improving the water holding capacity of starch gel. At the same time, nanocellulose can improve the flatness, smoothness and uniformity of the fresh-keeping coating on the fresh-keeping paper, thereby controlling the release rate and amount of chlorine dioxide, achieving stable release of chlorine dioxide, reducing explosive release, and thus better exerting the preservation effect of chlorine dioxide.

[0041] Water-based acrylic resin has excellent adhesion and film-forming properties. When mixed with the fresh-keeping coating, it can better adhere to the fresh-keeping base paper, forming a better bonding effect, which helps the uniform distribution and stable release of chlorine dioxide in the fresh-keeping paper, and improves the fresh-keeping effect. Casein is a calcium-phosphate binding protein with hydrophilic and hydrophobic groups in its molecular structure. This structure enables casein to form hydrogen bonds or other interactions with water molecules, enhancing the binding force between casein and water molecules, while preventing water penetration, thereby maintaining the integrity and water resistance of the fresh-keeping coating. Casein is extracted from milk, edible, non-toxic, harmless, formaldehyde-free, highly safe, and has strong adhesion and water resistance. It can be used in the preparation of fresh-keeping paper under various temperature and humidity conditions. As a surfactant, alkyl glycoside can improve the compatibility between materials, help the uniform dispersion and stable combination of various components in the cling film, and at the same time, alkyl glycoside has strong antibacterial activity, can inhibit the growth and reproduction of microorganisms, thereby extending the shelf life of fruits and vegetables. When making chlorine dioxide cling film, adding alkyl glycoside can further enhance the antibacterial ability of cling film and improve the preservation effect. The high-energy particles such as electrons and ions generated by the plasma equipment collide and react with the surface of water-based acrylic resin, casein, and alkyl glycoside, introduce new functional groups or segments, and improve the wettability of the surface of water-based acrylic resin, thereby improving its structural and functional properties, promoting the interaction and cross-linking reaction of water-based acrylic resin and other materials, and improving the interaction between various materials, thereby promoting the stable release of chlorine dioxide and improving the preservation effect.

[0042] Polyethylene glycol is a high molecular compound. Adding polyethylene glycol during the preparation of chlorine dioxide cling paper can make the cling coating more evenly coated on the cling base paper, thereby improving the cling effect of the cling paper. Polyethylene glycol has hygroscopicity and water retention. It can adjust the moisture content in the coating layer to a certain extent, thereby affecting the release rate of chlorine dioxide and enhancing the preservation effect. At the same time, polyethylene glycol has excellent antistatic and antioxidant properties, and can maintain the release amount of chlorine dioxide and the stability of the cling paper.

[0043] The invention applies the prepared chlorine dioxide fresh-keeping paper to the storage, transportation and fresh-keeping of blueberries, performs fresh-keeping treatment on the blueberries after being harvested from the perspectives of logistics, packaging and preservatives, realizes the integration of storage, transportation and sales of blueberries, and improves the quality and commodity value of blueberries.

[0044] The raw materials used in the present invention are all commercially available raw materials.

[0045] Embodiment 1:

[0046] A method for preparing chlorine dioxide cling film, comprising the following steps:

[0047] Step 1, preparation of gelatinized starch: weigh 60 parts by weight of distilled water and place it in a beaker, add 11 parts by weight of starch (wheat starch and corn starch in a mass ratio of 1.5:1) and 2 parts by weight of nanocellulose (nanocellulose particle size is 50-60nm) under 55°C water bath conditions, adjust the pH value to 10, add 0.4 parts by weight of hydrogen peroxide and 0.1 parts by weight of ferric sulfate, take out the beaker and place it in a magnetic stirrer at 60°C and 500r / min and stir for 28 minutes, then add 2.5 parts by weight of 30% sodium hydroxide solution, and place it in a 60°C water bath and stir for 28 minutes to obtain gelatinized starch.

[0048] Step 2: Weigh 14 parts by weight of water-based acrylic resin, 5 parts by weight of casein, and 0.8 parts by weight of alkyl polyglycoside, mix them evenly, place them in a plasma device for treatment for 210 seconds, place them in a beaker, add 255 parts by weight of distilled water, stir and mix, place them in a 60°C water bath, add 0.07 parts by weight of ammonium persulfate, stir for 25 minutes, and obtain a mixed solution. The charge density of the plasma device is 1200C / cm 3 , gas flow rate is 1.5L / min, pressure is 100kPa, and temperature is 55℃.

[0049] Step 3: Add the gelatinized starch obtained in step 1 to the mixed solution obtained in step 2, add polyethylene glycol when heated to 65° C., stir at a constant temperature for 20 minutes, adjust the pH value to 10, and obtain a composite starch glue.

[0050] Step 4: Place the composite starch glue obtained in step 3 in a 40° C. water bath, add 1.1 parts by weight of sodium chlorite, and stir for 5 minutes to mix evenly, to obtain a fresh-keeping coating A.

[0051] Step 5: Weigh 15 parts by weight of citric acid and dissolve it in 85 parts by weight of distilled water to prepare a fresh-keeping coating solution B.

[0052] Step 6: Apply the fresh-keeping coating liquid A evenly on the fresh-keeping base paper A twice, with an interval of 3 minutes between the two coatings and a coating amount of 330g / m 2 , place the coated fresh-keeping base paper A in a 40°C drying oven and dry for 10 minutes to obtain fresh-keeping coating liquid A paper, soak the fresh-keeping base paper B in the fresh-keeping coating liquid B for 60 seconds, take it out and place it in a 40°C drying oven and dry it for 8 minutes to obtain fresh-keeping coating liquid B paper, and laminate the side of the fresh-keeping coating liquid A paper coated with the fresh-keeping coating liquid A and the fresh-keeping coating liquid B paper to obtain chlorine dioxide fresh-keeping paper. The fresh-keeping base paper A and the fresh-keeping base paper B are food-grade absorbent paper with a thickness of 0.5-0.8mm, a length of 10-12cm, and a width of 5-6cm.

[0053] The application of chlorine dioxide cling film in the preservation of blueberries is processed by the following method and steps:

[0054] S1. After picking blueberries, place them at 15°C for 3.5 hours to dissipate the field heat, and select blueberries with uniform size, similar color, consistent maturity, no mechanical damage, and no pests or rot for preservation;

[0055] S2. Use a polyethylene terephthalate packaging box to package the blueberries treated in step S1, cut the chlorine dioxide fresh-keeping paper into the size of the blueberry packaging box lid and stick it on the inner side of the blueberry packaging box lid, stick the side of the fresh-keeping coating A paper that is not coated with the fresh-keeping coating A on the lid, and put the packaged blueberries into a foam box for transportation and storage.

[0056] Embodiment 2:

[0057] A method for preparing chlorine dioxide fresh-keeping paper specifically comprises the following steps:

[0058] Step 1, preparation of gelatinized starch: weigh 65 parts by weight of distilled water and place it in a beaker, add 13 parts by weight of starch (wheat starch and corn starch in a mass ratio of 2:1) and 3 parts by weight of nanocellulose (nanocellulose particle size is 50-60nm) under 58°C water bath conditions, adjust the pH value to 10, add 0.5 parts by weight of hydrogen peroxide and 0.15 parts by weight of ferric sulfate, take out the beaker and place it in a magnetic stirrer at 62°C and 550r / min and stir for 25 minutes, then add 2.8 parts by weight of 30% sodium hydroxide solution, and place it in a 62°C water bath and stir for 25 minutes to obtain gelatinized starch.

[0059] Step 2: Weigh 16 parts by weight of waterborne acrylic resin, 8 parts by weight of casein, and 1.2 parts by weight of alkyl polyglycoside, mix them evenly, place them in a plasma device for 180 seconds, place them in a beaker, add 260 parts by weight of distilled water, stir and mix, place them in a 62°C water bath, add 0.08 parts by weight of ammonium persulfate, stir for 22 minutes, and obtain a mixed solution. The charge density of the plasma device is 1300C / cm 3 , gas flow rate is 1.6L / min, pressure is 105kPa, and temperature is 60℃.

[0060] Step 3: Add the gelatinized starch obtained in step 1 to the mixed solution obtained in step 2, add polyethylene glycol when heated to 70° C., stir at a constant temperature for 25 minutes, adjust the pH value to 10, and obtain a composite starch glue.

[0061] Step 4: Place the composite starch glue obtained in step 3 in a 42° C. water bath, add 1.2 parts by weight of sodium chlorite, and stir for 5 minutes to mix evenly, to obtain a fresh-keeping coating A.

[0062] Step 5: Weigh 18 parts by weight of citric acid and dissolve it in 88 parts by weight of distilled water to prepare a fresh-keeping coating solution B.

[0063] Step 6: Apply the fresh-keeping coating liquid A evenly on the fresh-keeping base paper A twice, with an interval of 3 minutes between the two coatings and a coating amount of 340g / m 2 , place the coated fresh-keeping base paper A in a 45°C drying oven and dry for 8 minutes to obtain fresh-keeping coating liquid A paper, soak the fresh-keeping base paper B in the fresh-keeping coating liquid B for 70 seconds, take it out and place it in a 40°C drying oven and dry it for 6 minutes to obtain fresh-keeping coating liquid B paper, and laminate the side of the fresh-keeping coating liquid A paper coated with the fresh-keeping coating liquid A and the fresh-keeping coating liquid B paper to obtain chlorine dioxide fresh-keeping paper. The fresh-keeping base paper A and the fresh-keeping base paper B are food-grade absorbent paper with a thickness of 0.5-0.8mm, a length of 10-12cm, and a width of 5-6cm.

[0064] The application of chlorine dioxide cling film in the preservation of blueberries is processed by the following method and steps:

[0065] S1. After picking blueberries, place them at 16°C for 3.5 hours to dissipate the field heat, and select blueberries with uniform size, similar color, consistent maturity, no mechanical damage, and no pests or rot for preservation;

[0066] S2. Use a polyethylene terephthalate packaging box to package the blueberries treated in step S1, cut the chlorine dioxide fresh-keeping paper into the size of the blueberry packaging box lid and stick it on the inner side of the blueberry packaging box lid, stick the side of the fresh-keeping coating A paper that is not coated with the fresh-keeping coating A on the lid, and put the packaged blueberries into a foam box for transportation and storage.

[0067] Comparative Example 1:

[0068] The nanocellulose in Example 2 is removed, and the other method steps are the same as Example 2.

[0069] Comparative Example 2:

[0070] The alkyl glycoside in Example 2 is removed, and the other method steps are the same as those in Example 2.

[0071] Comparative Example 3:

[0072] The polyethylene glycol in Example 2 is removed, and the other method steps are the same as Example 2.

[0073] Comparative Example 4:

[0074] The second step of Example 2 is modified as follows: 16 parts by weight of aqueous acrylic resin, 8 parts by weight of casein, and 1.2 parts by weight of alkyl glycoside are weighed and placed in a beaker, 260 parts by weight of distilled water are added and stirred, and the mixture is placed in a 62° C. water bath, 0.08 parts by weight of ammonium persulfate are added, and the mixture is stirred for 22 minutes to obtain a mixed solution. The other method steps are the same as those of Example 2.

[0075] The fresh-keeping coating A paper prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 was tested for sodium chlorite retention rate using the iodine titration method. Fresh-keeping coating A paper and fresh-keeping coating B paper release chlorine dioxide when they are pasted together. Only when there is sodium chlorite on the fresh-keeping coating A paper will chlorine dioxide be released after the two papers are pasted together. Therefore, it is necessary to determine the sodium chlorite retention rate of fresh-keeping coating A paper during storage. Figure 2 As shown in the figure, the retention rate of sodium chlorite decreases with the increase of storage time. The retention rates of sodium chlorite of the fresh-keeping coating A paper prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 are 58.82%, 59.12%, 58.63%, 58.54%, 57.82% and 57.98% respectively when they are just made. After storage for 6 days, the retention amount of sodium chlorite of the fresh-keeping coating A paper prepared in Comparative Examples 1, 2 and 4 on the fresh-keeping 1 paper is significantly reduced (P<0.05). After storage for 10 days, the retention rates of sodium chlorite of the fresh-keeping coating A paper prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 are reduced by 35.89%, 33.27%, 54.89%, 48.33%, 52.40% and 50.43% respectively, indicating that nanocellulose, alkyl glycoside, polyethylene glycol and plasma treatment can effectively delay the decline rate of sodium chlorite.

[0076] The chlorine dioxide cling paper prepared in Examples 1 and 2 and Comparative Examples 1, 2, 3 and 4 was titrated with sodium thiosulfate solution to determine the chlorine dioxide release rate. The chlorine dioxide release rate was determined 2 days after the chlorine dioxide cling paper was prepared, and then measured every other day. Figure 3As shown, the chlorine dioxide release shows a trend of increasing first and then decreasing with the extension of storage time. The chlorine dioxide fresh-keeping paper made by comparative examples 1, 2, 3, and 4 releases the most chlorine dioxide on the 2nd day, which are 0.48mg, 0.52mg, 0.46mg, and 0.53mg, respectively. This is related to the sodium chlorite retention in the fresh-keeping paper. It may also be that sodium chlorite reacts rapidly with citric acid when the two papers are just attached, and the generated chlorine dioxide is quickly filled into the measurement container. The fresh-keeping paper made by embodiment 1 and embodiment 2 releases the most chlorine dioxide on the 4th day, which are 0.56mg and 0.58mg, respectively. The slow release of chlorine dioxide by fresh-keeping paper will be affected by the paper base structure and the environment of the fresh-keeping system. Nanocellulose has a higher specific surface area and more hydroxyl groups, can form a stronger interaction with water molecules, can form a dense network structure, and nanocellulose can improve the flatness, smoothness, and uniformity of the fresh-keeping coating on the fresh-keeping paper at the same time, thereby controlling the release of chlorine dioxide and realizing the stable release of chlorine dioxide. Alkyl polyglycoside can improve the compatibility between various materials and contribute to the uniform dispersion and stable combination of various components in the fresh-keeping paper. Polyethylene glycol can make the fresh-keeping coating liquid more evenly coated on the fresh-keeping base paper, and can adjust the moisture content in the coating layer to a certain extent, thereby affecting the release rate of chlorine dioxide. At the same time, polyethylene glycol has excellent antistatic and antioxidant properties, and can maintain the release amount of chlorine dioxide and the stability of the fresh-keeping paper. The high-energy particles such as electrons and ions generated by the plasma equipment collide and react with the surface of water-based acrylic resin, casein, and alkyl polyglycoside, introduce new functional groups or segments, improve their structure and functional properties, promote the interaction and cross-linking reaction between water-based acrylic resin and other materials, and enhance the interaction between the materials, thereby promoting the stable release of chlorine dioxide.

[0077] The chlorine dioxide cling film prepared in Example 2 and Comparative Examples 1, 2, 3 and 4 was pasted on the inner side of the lid of a polyethylene terephthalate packaging box, and the blueberries were placed at 16° C. for 3.5 hours after picking to dissipate the field heat, and then packed into packaging boxes. Each box of blueberries weighed (125±10) g, and was placed in a foam box and placed on an oscillator with a frequency of 1.08 Hz for 12 hours of simulated transportation. Then, the blueberries were stored at room temperature, and samples were taken every 2 days for determination of relevant physiological indicators. On day 0, the blueberries harvested on the same day after removing the field heat were used for determination of relevant indicators. The CK group was not treated with chlorine dioxide cling film, and the simulated transportation, packaging method and storage method of the blueberries in the CK group were the same as those in Example 2.

[0078] Figure 4 The hardness of blueberries was measured using a texture analyzer at two equatorial points of the blueberry fruit. The measurement depth was 7 mm and the measurement speed was 0.5 mm / s. The hardness of the blueberry fruit was expressed in Newton (N). Figure 4As shown in the figure, the hardness of blueberry fruit generally shows a downward trend during storage. Due to the increase in its post-ripening and metabolic rate, the activity of enzymes related to cell wall metabolism is increased, and the pectin substances in the cell wall are decomposed, which leads to a decrease in hardness. The hardness of blueberries in the CK group without chlorine dioxide cling film treatment decreases significantly. On the 6th day of storage, the hardness of blueberries in the CK group, Example 2, Comparative Examples 1, 2, 3, and 4 decreases by 30.7%, 19.4%, 24.9%, 26.0%, 31.6%, and 25.7%, respectively. On the 10th day of storage, the hardness of blueberries The temperatures of blueberry fruit were 0.91N, 1.17N, 1.03N, 1.01N, 0.99N and 1.08N, which were down by 43.6%, 31.4%, 38.6%, 38.3%, 42.3% and 36.2%, respectively. Chlorine dioxide cling film can help delay the decline of blueberry fruit firmness, inhibit the ripening and senescence of blueberry fruit, and thus delay the deterioration of its quality. Adding nanocellulose, alkyl glycoside and polyethylene glycol in the preparation process of chlorine dioxide cling film and plasma treatment is beneficial to the stable release of chlorine dioxide and prolong the shelf life of blueberries.

[0079] Figure 5 The rot rate of blueberries is determined by sensory evaluation. If there is any spot on the surface of the fruit where skin juice leaks out or mold is visible to the naked eye, it is considered rotten. The rot rate is calculated using the following formula: rot rate (%) = (number of rotten blueberries / total number of blueberries in each box) × 100%. Figure 5 As shown, under normal temperature conditions, as the storage time increases, the fruit decay rate shows an upward trend. During the storage period, the decay rate of blueberries in Example 2 is 3.7% on the 4th day, and the CK group reaches 7.7%. On the 8th day, the decay rates of blueberries in the CK group, Example 2, Comparative Examples 1, 2, 3, and 4 are 20.8%, 12.1%, 17.4%, 18.8%, 14.5%, and 13.9%, respectively. Chlorine dioxide cling film treatment of blueberries can effectively reduce the decay of blueberries, extend the shelf life of blueberries, and enhance their commercial value. In the preparation process of chlorine dioxide cling film, nanocellulose, alkyl glycoside, and polyethylene glycol are added, and plasma treatment is beneficial to the stable release of chlorine dioxide and reduces the decay rate of blueberries.

[0080] Figure 6The change of the color difference L value of blueberries. Color is an important factor affecting consumers' choice of fruit quality. The L value represents the brightness of the fruit. A higher L value indicates a brighter color, and a lower L value indicates a darker color. The L value was measured using a colorimeter. The colorimeter was first calibrated with a white board, and the lens of the colorimeter was aimed at the equator of the blueberry for measurement. The L value of blueberries gradually decreased with the extension of storage time. This may be because the blueberry fruit ripens and ages, and the content of anthocyanins and other pigments increases, which makes the surface color of the blueberry darker. On the 10th day of storage, the L value of blueberries decreased by 19.5%, 9.0%, 16.2%, 13.2%, 14.9% and 11.7% respectively. Chlorine dioxide cling film treatment of blueberries can effectively delay the decline of the brightness L of the blueberry fruit skin and ensure the freshness of blueberries.

[0081] Figure 7 To investigate the changes in soluble solids content during storage of blueberries, a handheld sugar meter was used to measure the soluble solids content. Soluble solids are an important criterion for evaluating the quality of blueberries. The main components of soluble solids are soluble sugars, including monosaccharides, disaccharides and soluble polysaccharides. Figure 7 As shown in the figure, during the storage period, the soluble solids content of blueberries first increased and then decreased. On the fourth day of storage, the soluble solids content of blueberries reached a peak and then showed a downward trend. This change is mainly due to the fact that during the storage process, the pectin, starch, cellulose and other components in the blueberry fruit are decomposed into soluble solids by the corresponding enzymes, but these soluble solids are then consumed by respiration. In the early stage of storage, the soluble solids formed by the ripening of blueberries are greater than the soluble solids consumed by respiration, and the soluble solids show an upward trend. As time goes by, the soluble solids formed are gradually less than the soluble solids consumed by respiration, so the content of soluble solids shows a downward trend. After storage for 10 days, the soluble solid contents of blueberries in the CK group, Example 2, Comparative Examples 1, 2, 3 and 4 were 10.20%, 11.97%, 10.70%, 10.50%, 10.57% and 10.53%, respectively. Adding nanocellulose, alkyl glycoside and polyethylene glycol in the preparation process of chlorine dioxide cling film and performing plasma treatment are beneficial to the stable release of chlorine dioxide, reducing the respiration of blueberries, delaying the rate of decrease of the soluble solid content of blueberries, and thus extending the shelf life of blueberries.

[0082] Figure 8The figure shows the changes of superoxide dismutase (SOD) during blueberry storage, and the SOD activity is expressed as U / g. The accumulation of superoxide free radicals in blueberry fruits can easily lead to blueberry cell damage. For self-protection, the body will produce a defense mechanism, and the related SOD activity will change. The balance between SOD activities is crucial to the survival of blueberry cells during storage. SOD is an antioxidant enzyme that plays a role in the scavenging of active oxygen free radicals and can effectively remove superoxide anions in cells. Figure 8 As shown in the figure, the activity of SOD in blueberries increases rapidly at the beginning of storage, but gradually decreases at the end of storage. The antioxidant capacity of blueberry fruit will gradually weaken. This is because as the fruit matures and ages, the metabolic activity inside the fruit gradually weakens, resulting in a decrease in the synthesis and activity of antioxidant enzymes. Chlorine dioxide cling film treatment of blueberries delayed the appearance of SOD peak and maintained a high SOD activity, improving the ability of blueberries to scavenge hydrogen peroxide and superoxide free radicals.

[0083] The minimum detection limit of chlorine dioxide in the standard GB 5009.244-2016 "Determination of Chlorine Dioxide in Food" is 0.65 mg / kg, and the quantitative limit of chlorine dioxide in fruits and vegetables is required to be 2.00 mg / kg. The residual chlorine dioxide in the samples of blueberries during storage was below 0.80 mg / kg, which met the standard requirements.

[0084] In summary, the chlorine dioxide cling paper prepared by the present invention can solve the problems of explosive release and short retention time of chlorine dioxide in chlorine dioxide cling paper, and use chlorine dioxide cling paper to preserve blueberries during transportation and storage after harvest, reduce the problems of blueberries being easily softened, rotted and deteriorated after harvest, extend the shelf life of blueberries, and improve their commodity value. Moreover, as a slow-release preservation technology, chlorine dioxide cling paper does not directly contact the product, is convenient and controllable, green and environmentally friendly, and safe, and can preserve blueberries.

[0085] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements or modifications made based on the present invention to solve basically the same technical problems and achieve basically the same technical effects are all included in the protection scope of the present invention.

Claims

1. A method for preparing chlorine dioxide cling film, characterized in that: The specific steps include: Step 1, preparation of gelatinized starch: weigh 60-65 parts by weight of distilled water and place it in a beaker, add 11-13 parts by weight of starch and 2-3 parts by weight of nanocellulose under 55-58° C. water bath conditions, adjust the pH value to 10, add 0.4-0.5 parts by weight of hydrogen peroxide and 0.1-0.15 parts by weight of ferric sulfate, take out the beaker and place it in a magnetic stirrer at 60-62° C. and 500-550 r / min, stir for 25-28 minutes, add 2.5-2.8 parts by weight of sodium hydroxide solution, and then place it in a water bath at 60-62° C. and stir for 25-28 minutes to obtain gelatinized starch; Step 2, weigh 14-16 parts by weight of water-based acrylic resin, 5-8 parts by weight of casein, and 0.8-1.2 parts by weight of alkyl polyglycoside, mix them evenly, place them in a plasma device for treatment for 180-210 seconds, place them in a beaker, add 255-260 parts by weight of distilled water, stir and mix, place them in a water bath at 60-62° C., add 0.07-0.08 parts by weight of ammonium persulfate, stir for 22-25 minutes, and obtain a mixed solution; Step 3, adding the gelatinized starch obtained in step 1 to the mixed solution obtained in step 2, adding polyethylene glycol when heated to 65-70° C., stirring at a constant temperature for 20-25 minutes, adjusting the pH value to 10, and obtaining a composite starch glue; Step 4: Place the composite starch glue obtained in step 3 in a water bath at 40-42° C., add 1.1-1.2 parts by weight of sodium chlorite, and stir for 4-5 minutes to mix evenly to obtain a fresh-keeping coating solution A; Step 5, weigh 15-18 parts by weight of citric acid and dissolve it in 85-88 parts by weight of distilled water to prepare a fresh-keeping coating liquid B; Step 6: Apply the fresh-keeping coating liquid A evenly on the fresh-keeping base paper A twice, with an interval of 3 minutes between the two coatings and a coating amount of 330-340 g / m 2 , place the coated fresh-keeping base paper A in a drying oven at 40-45°C for 8-10 minutes to obtain fresh-keeping coating liquid A paper, soak the fresh-keeping base paper B in the fresh-keeping coating liquid B for 60-70 seconds, take it out and place it in a drying oven at 40-45°C for 6-8 minutes to obtain fresh-keeping coating liquid B paper, and laminate the side of the fresh-keeping coating liquid A paper coated with the fresh-keeping coating liquid A with the fresh-keeping coating liquid B paper to obtain chlorine dioxide fresh-keeping paper.

2. The method for preparing a chlorine dioxide cling film according to claim 1, characterized in that: The starch is composed of wheat starch and corn starch in a mass ratio of 1.5 to 2:1, and the particle size of the nanocellulose is 50 to 60 nm.

3. The method for preparing a chlorine dioxide cling film according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 30%.

4. The method for preparing a chlorine dioxide cling film according to claim 1, characterized in that: The charge density of plasma equipment is 1200~1300C / cm 3 , gas flow rate is 1.5~1.6L / min, pressure is 100~105kPa, and temperature is 55~60℃.

5. The method for preparing a chlorine dioxide cling film according to claim 1, characterized in that: The fresh-keeping base paper A and the fresh-keeping base paper B are food-grade absorbent paper with a thickness of 0.5 to 0.8 mm, a length of 10 to 12 cm, and a width of 5 to 6 cm.

6. Use of the chlorine dioxide fresh-keeping paper prepared according to the method for preparing chlorine dioxide fresh-keeping paper according to any one of claims 1 to 5 in preserving blueberries.

7. The use of the chlorine dioxide cling paper in blueberry preservation according to claim 6, characterized in that: The following methods and steps are used to preserve blueberries: S1. After picking blueberries, place them at 15-16℃ for 3.5-4 hours to dissipate the field heat, and select blueberries with uniform size, similar color, consistent maturity, no mechanical damage, and no pests or rot for preservation; S2. Use a polyethylene terephthalate packaging box to package the blueberries treated in step S1, cut the chlorine dioxide cling film into the size of the blueberry packaging box cover and stick it on the inner side of the blueberry packaging box cover, and put the packaged blueberries into a foam box for transportation and storage.

8. The use of the chlorine dioxide cling paper in blueberry preservation according to claim 6, characterized in that: The side of the fresh-keeping coating A paper that is not coated with the fresh-keeping coating A is attached to the box cover.

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