CN108041406B - Composite preservative film and preparation method thereof - Google Patents
Composite preservative film and preparation method thereof Download PDFInfo
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/34—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals
- A23L3/3454—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals in the form of liquids or solids
- A23L3/3463—Organic compounds; Microorganisms; Enzymes
- A23L3/3562—Sugars; Derivatives thereof
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- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/34—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals
- A23L3/3454—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals in the form of liquids or solids
- A23L3/3463—Organic compounds; Microorganisms; Enzymes
- A23L3/3472—Compounds of undetermined constitution obtained from animals or plants
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/34—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals
- A23L3/3454—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by treatment with chemicals in the form of liquids or solids
- A23L3/358—Inorganic compounds
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D107/00—Coating compositions based on natural rubber
- C09D107/02—Latex
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- C08J2405/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2401/00 or C08J2403/00
- C08J2405/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
- Y02A40/90—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in food processing or handling, e.g. food conservation
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Abstract
The invention provides a composite preservative film and a preparation method thereof, the composite preservative film consists of an oxygen-blocking layer, an oxygen-removing layer and a preservative layer which are sequentially laminated from outside to inside, the oxygen-blocking layer is obtained by hot-pressing and film-forming an ethylene-vinyl alcohol copolymer, and the oxygen-removing layer is prepared from the following raw materials in parts by mass: 90-100 parts of natural rubber latex, 1-3 parts of natural essential oil and 0.1-2 parts of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid. The composite preservative film disclosed by the invention has excellent oxygen barrier property and mechanical property through the synergistic effect of the oxygen barrier layer, the oxygen isolation layer and the preservative layer, slows down the physiological metabolism and aging of fresh foods such as fruits and vegetables to a certain extent, inhibits the growth of spoilage-causing microorganisms, improves the preservation effect of the fresh foods such as fruits and vegetables, and effectively prolongs the quality guarantee period of the fresh foods such as fruits and vegetables.
Description
Technical Field
The invention belongs to the technical field of food preservation, and particularly relates to a composite preservative film for food packaging and storage and a preparation method thereof.
Background
At present, the means mainly adopted for food preservation at home and abroad are divided into three main categories of physics, chemistry and biology, and the preservation principle of each type of preservation technology is different, and the categories can be divided. Although different methods are adopted by different fresh-keeping measures, the method is carried out by regulating and controlling three major influencing factors (aging process, decay-causing microorganisms and self water evaporation) which influence the taste and the quality of the fruits: firstly, the fruit aging is inhibited or slowed down by controlling the respiration of the fruit; secondly, the growth of putrefying bacteria is inhibited to control the breeding of microorganisms; the purpose of controlling the evaporation of internal water is achieved by controlling the relative humidity of the environment and changing the structure of intercellular water.
The plastic packing film for food fresh keeping is produced with ethylene as main material and through polymerization reaction. At present, the known chitosan is a valuable natural polymer material, has a bacteriostatic effect, good film-forming properties and the like, and is widely researched as a preservative film. However, the single chitosan preservative film has an unobvious preservation effect, and a bacteriostatic agent or other additives are required to be added to improve the preservation and bacteriostatic effects.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a composite preservative film for food packaging and storage and a preparation method thereof.
The technical scheme of the invention is as follows:
the invention provides a composite preservative film which is composed of an oxygen-blocking layer, an oxygen-removing layer and a preservative layer which are sequentially laminated from outside to inside, wherein the oxygen-blocking layer is obtained by hot-pressing and film-forming an ethylene-vinyl alcohol copolymer, and the oxygen-removing layer is prepared from the following raw materials in parts by mass: 90-100 parts of natural rubber latex, 1-3 parts of natural essential oil and 0.1-2 parts of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid.
The composite preservative film is formed by compounding an oxygen-blocking layer, an oxygen-isolating layer and a preservative layer, and has excellent mechanical properties and functions of oxygen blocking, oxygen removal, antibiosis and preservation.
Preferably, the content of an ethylene chain segment in the ethylene-vinyl alcohol copolymer is 25-45%, and the alcoholysis degree is 96-100%.
Preferably, the solid content of the natural rubber latex is 40-50%.
Preferably, the natural essential oil is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil.
Preferably, the fresh-keeping layer comprises the following raw materials in parts by mass: 1-3 parts of chitosan, 2-6 parts of polyvinyl alcohol, 90-100 parts of acetic acid, 1-2 parts of glycerol and 0.1-0.5 part of natural essential oil. More preferably, the molecular weight of the polyvinyl alcohol is 10000-500000, and the alcoholysis degree is 90-100%. The natural essential oil is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil.
The invention also provides a preparation method of the composite preservative film, which comprises the following steps:
(1) carrying out hot pressing on the ethylene-vinyl alcohol copolymer to form a film so as to obtain an oxygen barrier layer;
(2) uniformly mixing the chitosan coating solution, pouring the mixture into a mold, drying, and removing the film to obtain a fresh-keeping layer;
(3) uniformly mixing the natural rubber latex, the natural essential oil and the cobalt salt in parts by mass to obtain a coating liquid;
(4) and (3) coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 25-35 ℃ for 1-2 h, then compounding the preservative layer on the coating liquid, and rolling by using a laminating machine to obtain the composite preservative film.
Preferably, in the step (1), the hot pressing temperature is 180-200 ℃, the pressure is 2-4 MPa, and the time is 3-5 min.
Preferably, in the step (2), after the coating liquid is poured into the mold, the mold is placed in a vacuum drying oven and is dried for 18-24 hours at the temperature of 25-35 ℃.
The invention has the beneficial effects that: the composite preservative film disclosed by the invention has excellent oxygen barrier property and mechanical property through the synergistic effect of the oxygen barrier layer, the oxygen isolation layer and the preservative layer, slows down the physiological metabolism and aging of fresh foods such as fruits and vegetables to a certain extent, inhibits the growth of spoilage-causing microorganisms, improves the preservation effect of the fresh foods such as fruits and vegetables, and effectively prolongs the quality guarantee period of the fresh foods such as fruits and vegetables.
Detailed Description
In order to more clearly illustrate the technical solution of the present invention, the technical solution of the present invention will be further illustrated with reference to the following specific embodiments:
one of the technical schemes provided by the invention is as follows:
the invention provides a composite preservative film which is composed of an oxygen-blocking layer, an oxygen-removing layer and a preservative layer which are sequentially laminated from outside to inside, wherein the oxygen-blocking layer is obtained by hot-pressing and film-forming an ethylene-vinyl alcohol copolymer, and the oxygen-removing layer is prepared from the following raw materials in parts by mass: 90-100 parts of natural rubber latex, 1-3 parts of natural essential oil and 0.1-2 parts of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid.
The composite preservative film is formed by compounding the oxygen barrier layer, the oxygen isolation layer and the preservative layer, and has excellent functions of oxygen barrier, oxygen removal, antibiosis and preservation.
The oxygen barrier layer is obtained by hot-pressing and film-forming an ethylene-vinyl alcohol copolymer, and the ethylene-vinyl alcohol copolymer has excellent gas barrier performance and other excellent performances (such as oil resistance, good organic solvent resistance, good glossiness, good printing performance and the like), so that the ethylene-vinyl alcohol copolymer has wide application in the food packaging field. However, the ethylene-vinyl alcohol copolymer has easy moisture absorption of hydroxyl, and the intermolecular force can be destroyed after moisture absorption, so that the gas barrier property is reduced, and the problem is well solved after the ethylene-vinyl alcohol copolymer is compounded with the oxygen barrier layer and the fresh-keeping layer.
The raw materials of the oxygen removing layer contain natural rubber latex which is a water-based colloid system of natural rubber, and the oxygen removing layer has strong self-adhesiveness, easy processability and good film forming property. The natural rubber takes poly cis-1, 4-isoprene as a main body, the molecular chain of the natural rubber contains a large amount of unsaturated double bonds, and the natural rubber can react with oxygen under certain catalytic conditions, so that the purpose of absorbing oxygen is achieved.
The fresh-keeping layer is a chitosan film, the limited antibacterial activity of the pure chitosan film cannot reach the sterilization level required by packaging, and the natural essential oil added in the invention can enhance the antibacterial activity and expand the application range.
Preferably, the content of an ethylene chain segment in the ethylene-vinyl alcohol copolymer is 25-45%, and the alcoholysis degree is 96-100%. The ethylene-vinyl alcohol copolymer has good oxygen barrier property, and can act synergistically with the oxygen barrier layer and the preservative layer after hot-pressing film forming, so that the prepared composite preservative film has excellent oxygen barrier property.
Preferably, the solid content of the natural rubber latex is 40-50%. The molecular chain of the natural rubber contains a large number of unsaturated double bonds, and the natural rubber can react with oxygen under certain catalytic conditions to generate a macromolecular polymer.
Preferably, the natural essential oil is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil. The above natural essential oils have inhibiting and eliminating effects on growth of pythium aphanidermatum and bacteria.
Preferably, the fresh-keeping layer comprises the following raw materials in parts by mass: 1-3 parts of chitosan, 2-6 parts of polyvinyl alcohol, 90-100 parts of acetic acid, 1-2 parts of glycerol and 0.1-0.5 part of natural essential oil. Wherein the chitosan forms a film with a certain strength.
Preferably, the molecular weight of the polyvinyl alcohol is 10000-500000, and the alcoholysis degree is 90-100%. The polyvinyl alcohol can well promote the film formation of the chitosan.
Preferably, the natural essential oil is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil. The natural essential oil is added, so that the fresh-keeping layer has good antibacterial property.
The second technical scheme provided by the invention is as follows:
the invention also provides a preparation method of the composite preservative film, which comprises the following steps:
(1) carrying out hot pressing on the ethylene-vinyl alcohol copolymer to form a film so as to obtain an oxygen barrier layer;
(2) uniformly mixing the chitosan coating solution, pouring the mixture into a mold, drying, and removing the film to obtain a fresh-keeping layer;
(3) uniformly mixing the natural rubber latex, the natural essential oil and the cobalt salt in parts by mass to obtain a coating liquid;
(4) and (3) coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 25-35 ℃ for 1-2 h, then compounding the preservative layer on the coating liquid, and rolling by using a laminating machine to obtain the composite preservative film.
The preparation method is simple, and the prepared composite preservative film has high tensile strength and excellent mechanical properties.
Wherein in the step (1), the hot pressing temperature is 180-200 ℃, the pressure is 2-4 MPa, and the time is 3-5 min. In the step (2), after the coating liquid is poured into a mould, the mould is placed in a vacuum drying oven and dried for 18-24h at the temperature of 25-35 ℃.
Example 1
The composite preservative film is sequentially laminated with an oxygen blocking layer, an oxygen removing layer and a preservative layer from outside to inside, wherein the oxygen blocking layer is obtained by hot-pressing and film forming of an ethylene-vinyl alcohol copolymer (the content of an ethylene chain segment is 25%, and the alcoholysis degree is 100%), and the oxygen removing layer is prepared from the following raw materials in parts by mass: 90 parts of natural rubber latex (solid content is 40%), 2 parts of tea tree essential oil and 2 parts of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid and comprises the following raw materials in parts by mass: 3 parts of chitosan, 4 parts of polyvinyl alcohol, 90 parts of acetic acid, 1 part of glycerol and 0.1 part of cinnamon essential oil.
The preparation method of the composite preservative film comprises the following steps:
(1) hot-pressing 4g of ethylene-vinyl alcohol copolymer in a mould for 3min to obtain an oxygen barrier layer, wherein the hot-pressing temperature is 180 ℃ and the pressure is 4 MPa;
(2) respectively weighing 3g of chitosan and 4g of polyvinyl alcohol, adding the chitosan and the polyvinyl alcohol into 90g of acetic acid solution (the volume fraction is 2%), adding 0.1g of cinnamon essential oil into the solution while stirring, and mechanically stirring for 30min to obtain a homogeneous solution; then adding 1g of glycerol, mechanically stirring for 1h to obtain a film-forming solution, standing the film-forming solution at room temperature for 4h until no bubbles exist, then pouring the mixed solution into a mold, placing the mold in a vacuum drying oven, drying the mold for 20h at 30 ℃ until the mold is completely dried, and removing the film to obtain a preservative layer;
(3) uniformly mixing 90g of natural rubber latex, 2g of tea tree essential oil and 2g of cobalt salt to obtain a coating liquid;
(4) and (3) coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 25 ℃ for 2h, then compounding the preservative layer on the coating liquid, and rolling for 3 times by using a laminating machine to obtain the composite preservative film.
The tensile strength of the composite preservative film prepared in the embodiment 1 is 112.38MPa, and is obviously improved compared with a comparative example, which shows that the mechanical property of the composite preservative film is obviously improved.
The composite preservative film is used for packaging cherry tomatoes, the rotting rate of the cherry tomatoes is 5% after the cherry tomatoes are stored for 10 days, the vitamin C retention rate is 72%, the composite preservative film is used for packaging grapes, the rotting rate of the grapes is 12% after the grapes are stored for 10 days, and the vitamin C retention rate is 93%; when the method is used for packaging spinach, after the spinach is stored for 10 days, the rotting rate of the spinach is 12%, and the retention rate of vitamin C is 94%; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 7%, and the vitamin C retention rate is 95%. The composite preservative film can effectively prolong the shelf life of food.
Example 2
The composite preservative film is sequentially laminated with an oxygen blocking layer, an oxygen removing layer and a preservative layer from outside to inside, wherein the oxygen blocking layer is obtained by hot-pressing and film forming of an ethylene-vinyl alcohol copolymer (the content of an ethylene chain segment is 35%, and the alcoholysis degree is 98%), and the oxygen removing layer is prepared from the following raw materials in parts by mass: 95 parts of natural rubber latex (solid content is 45%), 1 part of garlic essential oil, 2 parts of thyme essential oil and 0.5 part of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid and comprises the following raw materials in parts by mass: 2 parts of chitosan, 6 parts of polyvinyl alcohol, 95 parts of acetic acid, 1.5 parts of glycerol and 0.4 part of tea tree essential oil.
The preparation method of the composite preservative film comprises the following steps:
(1) hot-pressing 5g of ethylene-vinyl alcohol copolymer in a mould for 4min to obtain an oxygen barrier layer, wherein the hot-pressing temperature is 190 ℃ and the pressure is 3 MPa;
(2) respectively weighing 2g of chitosan and 6g of polyvinyl alcohol, adding the chitosan and the polyvinyl alcohol into 95g of acetic acid solution (the volume fraction is 2%), adding 0.4g of tea tree essential oil into the solution while stirring, and mechanically stirring for 30min to obtain a homogeneous solution; then adding 1.5g of glycerol, mechanically stirring for 1h to obtain a film-forming solution, standing the film-forming solution at room temperature for 4h until no bubbles exist, then pouring the mixed solution into a mould, placing the mould into a vacuum drying oven, drying for 24h at 25 ℃ until complete drying is realized, and removing the film to obtain a fresh-keeping layer;
(3) uniformly mixing 95g of natural rubber latex, 1g of garlic essential oil, 2g of thyme essential oil and 0.5g of cobalt salt to obtain a coating liquid;
(4) and (3) coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 30 ℃ for 1.5h, then compounding the preservative layer on the coating liquid, and rolling for 2 times by using a laminating machine to obtain the composite preservative film.
The tensile strength of the composite preservative film prepared in the embodiment 2 is 108.26MPa, and is obviously improved compared with the comparative example, which shows that the mechanical property of the composite preservative film is obviously improved.
The composite preservative film is used for packaging cherry tomatoes, the rotting rate of the cherry tomatoes is 5% after the cherry tomatoes are stored for 10 days, and the vitamin C retention rate is 74%; when the vitamin C is used for packaging grapes, the rotting rate of the grapes is 10% after the grapes are stored for 10 days, and the vitamin C retention rate is 94%; when the method is used for packaging spinach, after the spinach is stored for 10 days, the rotting rate of the spinach is 10%, and the vitamin C retention rate is 95%; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 6%, and the vitamin C retention rate is 96%. The composite preservative film can effectively prolong the shelf life of food.
Example 3
The composite preservative film is sequentially laminated with an oxygen blocking layer, an oxygen removing layer and a preservative layer from outside to inside, wherein the oxygen blocking layer is obtained by hot-pressing and film forming of an ethylene-vinyl alcohol copolymer (the content of an ethylene chain segment is 45%, and the alcoholysis degree is 96%), and the oxygen removing layer is prepared from the following raw materials in parts by mass: 100 parts of natural rubber latex (solid content is 40%), 1 part of tea tree essential oil and 0.1 part of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid and comprises the following raw materials in parts by mass: 1 part of chitosan, 2 parts of polyvinyl alcohol, 100 parts of acetic acid, 2 parts of glycerol, 0.2 part of cinnamon essential oil and 0.3 part of garlic essential oil.
The preparation method of the composite preservative film comprises the following steps:
(1) hot-pressing 6g of ethylene-vinyl alcohol copolymer in a mould for 5min to obtain an oxygen barrier layer, wherein the hot-pressing temperature is 220 ℃ and the pressure is 2 MPa;
(2) respectively weighing 1g of chitosan and 2g of polyvinyl alcohol, adding the chitosan and the polyvinyl alcohol into 100g of acetic acid solution (the volume fraction is 2%), adding 0.2g of cinnamon essential oil and 0.3g of garlic essential oil into the solution while stirring, and mechanically stirring for 30min to obtain a homogeneous solution; then adding 2g of glycerol, mechanically stirring for 1h to obtain a film-forming solution, standing the film-forming solution at room temperature for 4h until no bubbles exist, then pouring the mixed solution into a mould, placing the mould into a vacuum drying oven, drying the mould for 18h at 35 ℃ until the mould is completely dried, and removing the film to obtain a preservative layer;
(3) uniformly mixing 100g of natural rubber latex, 1g of tea tree essential oil and 0.1g of cobalt salt to obtain a coating liquid;
(4) and (3) coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 35 ℃ for 1h, then compounding the preservative layer on the coating liquid, and rolling for 4 times by using a laminating machine to obtain the composite preservative film.
The tensile strength of the composite preservative film prepared in the embodiment 3 is 110.5MPa, and is obviously improved compared with a comparative example, which shows that the mechanical property of the composite preservative film is obviously improved.
The composite preservative film is used for packaging cherry tomatoes, the rotting rate of the cherry tomatoes is 6% after the cherry tomatoes are stored for 10 days, and the vitamin C retention rate is 80%; when the vitamin C is used for packing grapes, the rotting rate of the grapes is 12% after the grapes are stored for 10 days, and the vitamin C retention rate is 94%; when the method is used for packaging spinach, after the spinach is stored for 10 days, the rotting rate of the spinach is 14%, and the vitamin C retention rate is 95%; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 8%, and the vitamin C retention rate is 95%. The composite preservative film can effectively prolong the shelf life of food.
Comparative example 1
A chitosan preservative film comprises the following raw materials in parts by mass: 3 parts of chitosan, 4 parts of polyvinyl alcohol, 90 parts of acetic acid, 1 part of glycerol and 0.1 part of cinnamon essential oil.
The preparation method of the chitosan preservative film comprises the following steps: respectively weighing 3g of chitosan and 4g of polyvinyl alcohol, adding the chitosan and the polyvinyl alcohol into 90g of acetic acid solution (the volume fraction is 2%), adding 0.1g of cinnamon essential oil into the solution while stirring, and mechanically stirring for 30min to obtain a homogeneous solution; and then adding 1g of glycerol, mechanically stirring for 1h to obtain a film forming solution, standing the film forming solution at room temperature for 4h until no bubbles exist, pouring the mixed solution into a mold, placing the mold in a vacuum drying oven, drying for 20h at 30 ℃ until complete drying is realized, and removing the film to obtain the chitosan preservative film.
The tensile strength of the chitosan preservative film prepared in the comparative example 1 is 60.77 MPa.
The chitosan preservative film is used for packaging cherry tomatoes, the rotting rate of the cherry tomatoes is 10% after the cherry tomatoes are stored for 10 days, and the vitamin C retention rate is 65%; the method is used for packaging grapes, the rotting rate of the grapes is 30% and the vitamin C retention rate is 90% after 10 days of storage, the rotting rate of the spinach is 42% and the vitamin C retention rate is 70% after 10 days of storage; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 25%, and the vitamin C retention rate is 83%.
Comparative example 2
A chitosan preservative film comprises the following raw materials in parts by mass: 3 parts of chitosan, 4 parts of polyvinyl alcohol, 90 parts of acetic acid, 1 part of glycerol and 0.1 part of tea tree essential oil.
The preparation method of the chitosan preservative film comprises the following steps: respectively weighing 3g of chitosan and 4g of polyvinyl alcohol, adding the chitosan and the polyvinyl alcohol into 90g of acetic acid solution (the volume fraction is 2%), adding 0.1g of tea tree essential oil into the solution while stirring, and mechanically stirring for 30min to obtain a homogeneous solution; and then adding 1g of glycerol, mechanically stirring for 1h to obtain a film forming solution, standing the film forming solution at room temperature for 4h until no bubbles exist, pouring the mixed solution into a mold, placing the mold in a vacuum drying oven, drying for 20h at 30 ℃ until complete drying is realized, and removing the film to obtain the chitosan preservative film.
The tensile strength of the chitosan preservative film prepared in the comparative example 2 is 81.25 MPa.
The chitosan preservative film is used for packaging cherry tomatoes, the rotting rate of the cherry tomatoes is 10% after the cherry tomatoes are stored for 10 days, and the vitamin C retention rate is 62%; the vitamin C preservative is used for packing grapes, the rotting rate of the grapes is 30% after the grapes are stored for 10 days, and the vitamin C retention rate is 86%; the vitamin C preservative is used for packing grapes, the rotting rate of the grapes is 30% after the grapes are stored for 10 days, and the vitamin C retention rate is 86%; when the method is used for packaging spinach, after the spinach is stored for 10 days, the rotting rate of the spinach is 40%, and the vitamin C retention rate is 80%; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 20%, and the vitamin C retention rate is 85%.
Comparative example 3
The tensile strength of the common PE preservative film is 18.20 MPa.
The common PE preservative film is used for packaging the cherry tomatoes, the rotting rate of the cherry tomatoes is 40% after the cherry tomatoes are stored for 10 days, and the vitamin C retention rate is 48%; the common PE preservative film is used for packaging grapes, the rotting rate of the grapes is 50% after 10 days of storage, the vitamin C retention rate is 75%, the PE preservative film is used for packaging spinach, the rotting rate of the spinach is 58% after 10 days of storage, and the vitamin C retention rate is 63%; when the vitamin C is used for packaging the green beans, the rotting rate of the green beans after 10 days of storage is 42%, and the vitamin C retention rate is 45%.
The above description is not intended to limit the present invention, but rather, the present invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.
Claims (9)
1. The composite preservative film is characterized by comprising an oxygen-blocking layer, an oxygen-removing layer and a preservative layer which are sequentially laminated from outside, wherein the oxygen-blocking layer is obtained by hot-pressing and film-forming an ethylene-vinyl alcohol copolymer, and the oxygen-removing layer is prepared from the following raw materials in parts by mass: 90-100 parts of natural rubber latex, 1-3 parts of natural essential oil and 0.1-2 parts of cobalt salt, wherein the fresh-keeping layer is prepared from chitosan coating liquid and comprises the following raw materials in parts by mass: 1-3 parts of chitosan, 2-6 parts of polyvinyl alcohol, 90-100 parts of acetic acid, 1-2 parts of glycerol and 0.1-0.5 part of natural essential oil.
2. The composite preservative film according to claim 1, wherein the content of ethylene chain segments in the ethylene-vinyl alcohol copolymer is 25-45%, and the alcoholysis degree is 96-100%.
3. The composite preservative film according to claim 1, wherein the natural rubber latex has a solid content of 40-50%.
4. The composite preservative film according to claim 1, wherein the natural essential oil in the oxygen removing layer is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil.
5. The composite plastic wrap of claim 1, wherein the polyvinyl alcohol has a molecular weight of 10000-500000 and an alcoholysis degree of 90-100%.
6. The composite preservative film according to claim 1, wherein the natural essential oil in the preservative layer is one or more of tea tree essential oil, cinnamon essential oil, spearmint essential oil, oregano essential oil, clove basil essential oil, garlic essential oil and thyme essential oil.
7. A method for preparing the composite wrap of any one of claims 1 to 6, comprising the steps of:
(1) hot pressing ethylene-vinyl alcohol copolymer to form film to obtain the oxygen barrier layer;
(2) uniformly mixing the chitosan coating solution, pouring the mixture into a mold, drying, and removing the film to obtain a fresh-keeping layer;
(3) uniformly mixing the natural rubber latex, the natural essential oil and the cobalt salt in parts by mass to obtain a coating liquid;
(4) and coating the coating liquid on the upper surface of the oxygen barrier layer, airing at 25-35 ℃ for 1-2 h, then compounding the preservative layer on the coating liquid, and rolling by using a laminating machine to obtain the composite preservative film.
8. The preparation method of the composite preservative film according to claim 7, wherein in the step (1), the hot pressing temperature is 180-200 ℃, the pressure is 2-4 MPa, and the time is 3-5 min.
9. The method for preparing a composite preservative film according to claim 7, wherein in the step (2), after the coating liquid is poured into the mold, the mold is placed in a vacuum drying oven and dried for 18-24 hours at the temperature of 25-35 ℃.
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