CN113354930B - Degradable preservative film and preparation method and application thereof - Google Patents

Degradable preservative film and preparation method and application thereof Download PDF

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CN113354930B
CN113354930B CN202110635276.7A CN202110635276A CN113354930B CN 113354930 B CN113354930 B CN 113354930B CN 202110635276 A CN202110635276 A CN 202110635276A CN 113354930 B CN113354930 B CN 113354930B
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chitosan
solution
polyethylene glycol
graft copolymer
caffeic acid
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CN113354930A (en
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裴斐
韩萍
胡秋辉
杨文建
方东路
马宁
姜建新
杨华平
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Nanjing University of Finance and Economics
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Nanjing University of Finance and Economics
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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
    • B65D65/38—Packaging materials of special type or form
    • B65D65/46—Applications of disintegrable, dissolvable or edible materials
    • B65D65/466—Bio- or photodegradable packaging materials
    • 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
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
    • 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
    • C08J2451/00—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers
    • C08J2451/02—Characterised by the use of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives of such polymers grafted on to polysaccharides
    • 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
    • C08J2471/00—Characterised by the use of polyethers obtained by reactions forming an ether link in the main chain; Derivatives of such polymers
    • C08J2471/02—Polyalkylene oxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
    • Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics

Abstract

The invention belongs to the technical field of composite materials, and particularly relates to a degradable preservative film and a preparation method and application thereof. The invention provides a degradable preservative film which comprises a polylactic acid base film, polyethylene glycol contained in the polylactic acid base film and chitosan-caffeic acid graft copolymer. In the invention, the chitosan-caffeic acid graft copolymer can destroy the compact structure of polylactic acid, so that the air permeability of the degradable preservative film is improved, the moisture resistance of the degradable preservative film is further improved, the quality degradation of edible fungi under the packaging of the degradable preservative film is inhibited, and the shelf life of the edible fungi is prolonged. In the invention, the polylactic acid has good biocompatibility and degradability as a base material, and the degradable preservative film has degradability by using the polylactic acid as the base material.

Description

Degradable preservative film and preparation method and application thereof
Technical Field
The invention belongs to the technical field of composite materials, and particularly relates to a degradable preservative film and a preparation method and application thereof.
Background
Edible fungi (Edable fungus) are Edible large fungi, have fleshy or colloid fruiting bodies, are delicious in taste and rich in nutrition, and are rich in various amino acids, vitamins, minerals and the like. However, since the fresh edible fungi has high water content, strong metabolism and respiration are still carried out after harvesting, and quality deterioration phenomena such as enzymatic browning, water immersion of tissues, even decay and deterioration are easily caused in the process of storage and transportation, and finally the edible quality and commodity value are lost. Therefore, a practical and effective preservation mode is found, and the inhibition of the quality deterioration of the harvested edible fungi is a key problem to be solved urgently in the edible fungi industry.
Packaging and fresh keeping are common means for prolonging the shelf life of edible fungi. The common packaging materials at present are petroleum-based plastic packaging materials, natural polymer packaging materials and the like. The petroleum-based plastic packaging material has the advantages of low cost, good mechanical property, strong barrier property and good heat sealing property, but is difficult to degrade and recycle and can pollute the environment. Although the natural polymer packaging materials (such as protein, carbohydrate and lipid) can be biodegraded, the moisture resistance is poor, and the fresh-keeping effect is poor. Therefore, the prior art is lack of a degradable packaging material with high moisture resistance for packaging and preserving the edible fungi.
Disclosure of Invention
In view of the above, the invention provides a degradable preservative film and a preparation method and application thereof, and the degradable preservative film provided by the invention has better humidity resistance and is beneficial to the preservation and storage of edible fungi; meanwhile, the degradable preservative film provided by the invention is degradable and environment-friendly.
In order to solve the above technical problems, the present invention provides a degradable preservative film comprising a polylactic acid-based film, polyethylene glycol and a chitosan-caffeic acid graft copolymer contained in the polylactic acid-based film.
Preferably, the mass ratio of the polylactic acid-based membrane to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 82-88: 10: 2-8.
Preferably, the thickness of the degradable preservative film is 0.0146-0.0188 mm.
The invention also provides a preparation method of the degradable preservative film in the technical scheme, which comprises the following steps:
dissolving a chitosan-caffeic acid graft copolymer and polyethylene glycol blend in chloroform to obtain a blended solution;
dissolving polylactic acid in trichloromethane to obtain a polylactic acid solution;
adding the blending solution into a polylactic acid solution to obtain a coating solution;
and forming a film by using the coating liquid to obtain the degradable preservative film.
Preferably, the particle size of the chitosan-caffeic acid graft copolymer and the particle size of the polyethylene glycol are independently 106 μm or less.
Preferably, the chitosan-caffeic acid graft copolymer and the polyethylene glycol before dissolution further comprise: preparing a chitosan-caffeic acid graft copolymer and polyethylene glycol to obtain a blend of the chitosan-caffeic acid graft copolymer and the polyethylene glycol;
the preparation method of the blend of the chitosan-caffeic acid graft copolymer and polyethylene glycol comprises the following steps:
mixing the chitosan-caffeic acid graft copolymer, polyethylene glycol and water to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
and drying the chitosan-caffeic acid graft copolymer and the aqueous solution of polyethylene glycol, and then sequentially grinding and sieving to obtain the blend.
Preferably, the total mass concentration of the chitosan-caffeic acid graft copolymer and the polyethylene glycol in the blending solution is 0.01-0.02 g/mL.
Preferably, the mass concentration of the polylactic acid in the polylactic acid solution is 0.11-0.13 g/mL.
Preferably, the thickness of the wet film obtained by film formation is 0.9-1.1 mm.
The invention also provides the application of the degradable preservative film in the technical scheme or the degradable preservative film prepared by the preparation method in the technical scheme in preserving packaged edible fungi.
The invention provides a degradable preservative film which comprises a polylactic acid base film, polyethylene glycol contained in the polylactic acid base film and chitosan-caffeic acid graft copolymer. In the invention, the chitosan-caffeic acid graft copolymer has good antioxidant and bacteriostatic effects, and the chitosan-caffeic acid graft copolymer can destroy the compact structure of polylactic acid, so that the air permeability of the degradable preservative film is improved, the moisture resistance of the degradable preservative film is further improved, and the shelf life of edible fungi is prolonged. In the invention, the polylactic acid has good biocompatibility and degradability as a base material, and the degradable preservative film has degradability by using the polylactic acid as the base material.
The invention also provides a preparation method of the degradable preservative film in the technical scheme, which comprises the following steps: dissolving a chitosan-caffeic acid graft copolymer and polyethylene glycol blend in chloroform to obtain a blended solution; dissolving polylactic acid in trichloromethane to obtain a polylactic acid solution; adding the blending solution into a polylactic acid solution to obtain a coating solution; and forming a film by using the coating liquid to obtain the degradable preservative film. According to the invention, by adopting a solvent blending method and adopting polyethylene glycol as a compatibilizer to introduce the chitosan-caffeic acid graft copolymer into polylactic acid, the water vapor transmission rate of the degradable preservative film is improved, so that the moisture resistance of the degradable preservative film is improved, the quality deterioration of edible fungi in the package of the degradable preservative film is inhibited, and the shelf life of the edible fungi is prolonged.
Drawings
FIG. 1 is a graph comparing the degradation rates of the wrap films of example 1 and comparative example 2, wherein (a) is a graph of the degradation rate of the degraded wrap film of example 1 in a hydrochloric acid degradation solution; (b) is a graph of the degradation rate of the preservative film of the comparative example 2 in the hydrochloric acid degradation solution; (c) a degradation rate curve chart of the degradation preservative film in the sodium hydroxide degradation solution in the embodiment 1 is shown; (d) is a degradation rate curve chart of the preservative film of the comparative example 2 in the sodium hydroxide degradation solution;
FIG. 2 is a graph showing a comparison of color difference values after keeping the Agaricus bisporus in the plastic wrap of example 1 and comparative examples 2 and 3, wherein (e) is a comparison graph of L; (f) comparative plot for Δ E; (g) is a comparative graph of BI;
FIG. 3 is a graph showing a comparison of the headspace air contents after the Agaricus bisporus is preserved by the plastic wrap of example 1 and comparative examples 2 and 3, wherein (m) is a comparison graph of oxygen concentration; (n) is a comparative plot of carbon dioxide concentration;
FIG. 4 is a graph showing the comparison of hardness between the wrap-retaining agaricus bisporus of example 1 and comparative examples 2 and 3;
FIG. 5 is a graph showing the comparison of the respiration rates of the wrap-retaining agaricus bisporus of example 1 and comparative examples 2 and 3;
FIG. 6 is a diagram showing the example 1 and the comparative examples 2 and 3 after 0, 3, 6, 9, 12 and 15 days.
Detailed Description
The invention provides a degradable preservative film which comprises a polylactic acid base film, polyethylene glycol contained in the polylactic acid base film and chitosan-caffeic acid graft copolymer.
In the present invention, the chitosan-caffeic acid graft copolymer is preferably prepared according to the following method:
dissolving chitosan and 1-hydroxybenzotriazole in an acetic acid aqueous solution to obtain a chitosan solution;
mixing caffeic acid ethanol solution, 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution and chitosan solution for coupling reaction to obtain the chitosan-caffeic acid graft copolymer.
The invention dissolves chitosan and 1-hydroxybenzotriazole in acetic acid aqueous solution to obtain chitosan solution. In the invention, the mass ratio of the chitosan to the 1-hydroxybenzotriazole is preferably 0.5: 1.04-1.08, more preferably 0.5: 1.05 to 1.07. In the invention, the volume concentration of the acetic acid aqueous solution is preferably 1.8-2.2%, and more preferably 1.9-2%. In the invention, the volume ratio of the mass of the chitosan to the volume of the acetic acid aqueous solution is preferably 0.5g: 48-52 mL, and more preferably 0.5g: 49-50 mL. In the invention, the dissolution is preferably carried out under the condition of stirring, and the rotating speed of the stirring is preferably 500-700 r/min, and more preferably 590-610 r/min; the time is preferably 12 to 24 hours, and more preferably 15 to 20 hours.
In the present invention, the 1-hydroxybenzotriazole as a racemization inhibitor enables to obtain CA-g-CS with a higher graft ratio.
After the chitosan solution is obtained, the caffeic acid ethanol solution, the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution and the chitosan solution are mixed for coupling reaction to obtain the chitosan-caffeic acid graft copolymer. In the present invention, the caffeic acid ethanol solution is preferably obtained by dissolving caffeic acid in absolute ethanol. In the present invention, the volume ratio of the mass of caffeic acid to absolute ethyl alcohol is preferably 0.6-0.63 g:2mL, more preferably 0.61-0.62 g:2 mL. In the invention, the dissolution is preferably carried out under the condition of ultrasound, and the frequency of the ultrasound is preferably 37-70 kHz, and more preferably 37 kHz; the time is preferably 15 to 30min, and more preferably 18 to 22 min.
In the present invention, the ethanol solution of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride is preferably obtained by dissolving 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride in absolute ethanol. In the present invention, the volume ratio of the mass of the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride to the absolute ethyl alcohol is preferably 1.5 to 1.53 g/2 mL, and more preferably 1.51 to 1.52 g/2 mL. In the invention, the dissolution is preferably carried out under the condition of ultrasound, and the frequency of the ultrasound is preferably 37-70 kHz, and more preferably 37 kHz; the time is preferably 15 to 30min, and more preferably 18 to 22 min.
In the invention, the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride is used as a cross-linking agent for promoting the connection between amino groups on the chitosan main chain and phenolic acid in the form of amide bonds.
In the invention, the volume ratio of the caffeic acid ethanol solution, the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution and the chitosan solution is preferably 1:1: 23-27, and more preferably 1:1: 24-25. In the present invention, the mixing is preferably performed by adding dropwise the caffeic acid ethanol solution and the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution to the chitosan solution. In the invention, the dripping speed is preferably 50-70 drops/min, and more preferably 55-65 drops/min. In the present invention, the dropping is preferably accompanied by stirring, and the rotation speed of the stirring is preferably 500 to 700r/min, more preferably 590 to 610 r/min.
In the present invention, the coupling reaction is preferably carried out under protection from light. The light-shielding mode is not particularly limited, as long as light shielding can be realized, and in the embodiment of the invention, the light-shielding mode is a mode of wrapping the reaction vessel by using tin foil paper. In the invention, the coupling reaction time is preferably 22-26 h, and more preferably 24-25 h.
In the present invention, the coupling reaction preferably further comprises:
carrying out solid-liquid separation on the product of the coupling reaction, and taking supernatant;
mixing the supernatant with a hydrochloric acid solution and dialyzing to obtain a dialysate;
and drying the dialysate to obtain the chitosan-caffeic acid graft copolymer.
The invention carries out solid-liquid separation on the product of the coupling reaction and takes the supernatant. In the present invention, the solid-liquid separation is preferably centrifugation. In the invention, the rotating speed of the centrifugation is preferably 9800-10200 r/min, and more preferably 10000-10100 r/min; the time is preferably 13 to 17min, and more preferably 15 to 16 min.
After the supernatant is obtained, the supernatant and the hydrochloric acid solution are mixed and dialyzed to obtain the dialysate. In the invention, the mass concentration of the hydrochloric acid solution is preferably 10-12 mol/L, and more preferably 11-11.5 mol/L; the volume ratio of the supernatant to the hydrochloric acid solution is preferably 100: 3-4, more preferably 100: 3.5. the mixing is not particularly limited in the present invention as long as it can be mixed uniformly.
In the invention, the dialysis time is preferably 70-74 h, more preferably 72-73 h; the pore size of the dialysis bag for dialysis is preferably 14000 Da. In the dialysis process, water is preferably changed every 7.5-8.5 hours, and more preferably 8-8.2 hours.
After obtaining the dialysate, the invention dries the dialysate to obtain the chitosan-caffeic acid graft copolymer. In the invention, the drying is preferably freeze-drying, and the freeze-drying time is preferably 48-60 h, and more preferably 51-57 h.
In the present invention, the molecular weight of the polyethylene glycol is preferably 4000, 6000 or 8000, more preferably 8000.
In the present invention, the polylactic acid is preferably 4032D available from Nature Works, USA. In the present invention, the 4032D is readily soluble in chloroform.
In the invention, the mass ratio of the polylactic acid to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is preferably 82-88: 10: 2-8, and more preferably 84-86: 10: 4-6. In the invention, the mass ratio of the polylactic acid to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 82:10:8, 84:10:6, 86:10:4 or 88:10: 2.
In the invention, the thickness of the degradable preservative film is preferably 0.0146-0.0188 mm, and more preferably 0.0160-0.0170 mm.
Compared with the traditional packaging material, the degradable preservative film prepared by the invention has obvious advantages in the aspects of bacteriostasis, antioxidation, modified atmosphere, degradability and the like, and the preservation effect can be realized by the adsorption reaction of phenolic acid in the packaging material and environmental oxygen free radicals or the inhibition of the growth of microorganisms in the storage environment.
The invention also provides a preparation method of the degradable preservative film in the technical scheme, which comprises the following steps:
dissolving a chitosan-caffeic acid graft copolymer and polyethylene glycol blend in chloroform to obtain a blended solution;
dissolving polylactic acid in trichloromethane to obtain a polylactic acid solution;
adding the blending solution into a polylactic acid solution to obtain a coating solution;
and forming a film by using the coating liquid to obtain the degradable preservative film.
The invention dissolves the chitosan-caffeic acid graft copolymer and polyethylene glycol blend in chloroform to obtain a blended solution. In the present invention, the method for preparing the blend of chitosan-caffeic acid graft copolymer and polyethylene glycol preferably comprises the following steps:
mixing the chitosan-caffeic acid graft copolymer, polyethylene glycol and water to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
and drying the chitosan-caffeic acid graft copolymer and the aqueous solution of polyethylene glycol, and then sequentially grinding and sieving to obtain the blend.
The invention mixes the chitosan-caffeic acid graft copolymer, polyethylene glycol and water to obtain the aqueous solution of the chitosan-caffeic acid graft copolymer and the polyethylene glycol. In the present invention, the water is preferably ultrapure water. In the present invention, the mixing preferably comprises the steps of:
dissolving the chitosan-caffeic acid graft copolymer in partial water to obtain a copolymer solution;
dissolving polyethylene glycol in the rest water to obtain polyethylene glycol aqueous solution;
first mixing the copolymer solution and the aqueous polyethylene glycol solution.
The invention dissolves the chitosan-caffeic acid graft copolymer in partial water to obtain copolymer solution. In the invention, the mass percentage of the part of water in the total water is 28-62%, and the preferable mass percentage is 40-45%. In the present invention, the ratio of the mass of the chitosan-caffeic acid graft copolymer to the volume of part of water is preferably 1 g: 90-120 mL, more preferably 1 g: 100-110 mL. In the invention, the dissolution is preferably carried out under the condition of ultrasound, and the frequency of the ultrasound is preferably 37-70 kHz, and more preferably 37 kHz; the time is preferably 28-32 min, and more preferably 30 min.
The invention dissolves polyethylene glycol in the rest water to obtain polyethylene glycol aqueous solution. In the present invention, the ratio of the mass of the polyethylene glycol to the volume of part of water is preferably 1 g: 40-60 mL, more preferably 1 g: 45-50 mL. In the invention, the dissolution is preferably carried out under the condition of magnetic stirring, and the rotating speed of the magnetic stirring is preferably 500-700 r/min, and more preferably 600-650 r/min; the time is preferably 28-32 min, and more preferably 30 min.
After obtaining the copolymer solution and the polyethylene glycol aqueous solution, the invention mixes the copolymer solution and the polyethylene glycol aqueous solution for the first time. In the invention, the volume ratio of the copolymer solution to the polyethylene glycol aqueous solution is preferably 1-4: 2.5, and more preferably 2-3: 2.5. In the invention, the temperature of the first mixing is preferably 20-30 ℃, and more preferably 25-28 ℃; the first mixing is preferably carried out under the condition of stirring, the stirring is preferably magnetic stirring, and the stirring time is preferably 0.8-1.2 h, and more preferably 0.9-1 h.
After the aqueous solution of the chitosan-caffeic acid graft copolymer and the polyethylene glycol is obtained, the aqueous solution of the chitosan-caffeic acid graft copolymer and the polyethylene glycol is dried, ground and sieved in sequence to obtain the blend. In the present invention, it is preferable that the drying step further includes: and (3) evaporating the water solution of the chitosan-caffeic acid graft copolymer and polyethylene glycol. In the present invention, the solution is viscous after the water is evaporated. In the invention, the temperature of the water evaporation is preferably 85-92 ℃, and more preferably 88-90 ℃. In the present invention, the temperature at which the water evaporates is preferably achieved by means of a water bath. The time for evaporating the water is not particularly limited, as long as the solution is viscous. The invention can remove part of water in the aqueous solution of the chitosan-caffeic acid graft copolymer and the polyethylene glycol by water evaporation to reduce the drying time. In the invention, the drying temperature is preferably 55-62 ℃, and more preferably 58-60 ℃; the time is preferably 12 to 24 hours, and more preferably 18 to 22 hours.
In the present invention, the method further preferably comprises, before the grinding: the material to be ground is immersed in liquid nitrogen. The invention has no special requirement on the dosage of the liquid nitrogen, as long as the object to be ground can be completely immersed. The method and the device have the advantages that the object to be ground is soaked in the liquid nitrogen to be cooled, so that the brittleness of the object to be ground is improved, and the grinding is facilitated. In the invention, the soaking time is preferably 8-12 min, and more preferably 10-11 min. The grinding mode is not particularly limited in the invention, and the grinding mode which is conventional in the field can be adopted. In an embodiment of the invention, the milling is performed in a hybrid ball mill.
In the present invention, the aperture of the sieve is preferably 150 mesh. The undersize is preferably taken after the sieving of the invention.
In the present invention, said sieving preferably further comprises: the sieved product is dried. In the invention, the drying temperature is preferably 55-62 ℃, and more preferably 58-60 ℃; the time is preferably 1.8 to 2.2 hours, and more preferably 2 to 2.1 hours.
In the invention, the particle size of the chitosan-caffeic acid graft copolymer and the particle size of the polyethylene glycol in the blend are independent, preferably 106 microns or less, and more preferably 102-100 microns. In the invention, the mass concentration of the blending solution is preferably 0.01-0.02 g/mL, and more preferably 0.013-0.018 g/mL.
In the invention, the chitosan-caffeic acid graft copolymer and the polyethylene glycol blend are dissolved in chloroform preferably under the ultrasonic condition, and the ultrasonic frequency is preferably 37-70 kHz, more preferably 37 kHz; the time is preferably 28 to 32min, and more preferably 30 to 31 min. In the present invention, the sonication is preferably carried out in an ice-water bath. The invention can prevent chloroform from volatilizing due to temperature rise by carrying out ultrasound in ice-water bath.
In the invention, the chitosan-caffeic acid graft copolymer and the polyethylene glycol in the polyethylene glycol blend are coated with the chitosan-caffeic acid graft copolymer to improve the interfacial property, so that the chitosan-caffeic acid graft copolymer is favorably dispersed in polylactic acid, thereby achieving the effect of compatibilization.
The polylactic acid is dissolved in the trichloromethane to obtain the polylactic acid solution. In the invention, the mass concentration of the polylactic acid solution is preferably 0.11-0.13 g/mL, and more preferably 0.12-0.126 g/mL. In the present invention, the dissolution of the polylactic acid in chloroform is preferably performed under stirring conditions; the stirring temperature is preferably room temperature, and more preferably 20-25 ℃. In the invention, the stirring is preferably magnetic stirring, and the rotating speed of the magnetic stirring is preferably 500-700 r/min, and more preferably 550-650 r/min.
After obtaining the blending solution and the polylactic acid solution, the blending solution is added into the polylactic acid solution to obtain the coating solution. In the invention, the volume ratio of the blending solution to the polylactic acid solution is preferably 3.3-3.7: 4.5, and more preferably 3.5-3.6: 4.5. In the invention, the addition is preferably carried out under the condition of stirring, and the stirring time is preferably 8-12 h, and more preferably 10-11 h. In the present invention, the stirring is preferably magnetic stirring. In the present invention, it is also preferable that the addition of the blend solution to the polylactic acid solution comprises: and (4) defoaming the mixed product. In the present invention, the debubbling is preferably performed under ultrasonic conditions; the frequency of the ultrasonic wave is preferably 37-70 kHz, and more preferably 37 kHz; the time is preferably 28 to 32min, and more preferably 30 to 31 min. In the present invention, the ultrasound is preferably performed in an ice-water bath to avoid volatilization of chloroform. In the invention, the degradable preservative film can be ensured to be complete, and the situation that the integrity of the preservative film is damaged due to foaming in the coating liquid (holes can be formed after the coating liquid is foamed) is avoided.
According to the invention, the blending solution is added into the polylactic acid solution, so that the phenomenon that the polylactic acid in the polylactic acid solution attracts the chitosan-caffeic acid graft copolymer in the blending solution to be coagulated can be avoided.
After the film coating liquid is obtained, the degradable preservative film is obtained by forming a film from the film coating liquid. In the invention, the film forming is preferably to pour the coating liquid into a mold for volatilization, and dry the obtained wet film to obtain the degradable preservative film. In the present invention, the mold is preferably a stainless steel disk. The shape and the size of the mould are not required to be special, and the mould can be set according to the requirement of the degradable preservative film. In the embodiment of the invention, the stainless steel disc is rectangular, and the size of the rectangle is 31cm multiplied by 15 cm. In the present invention, the thickness of the wet film obtained by the film formation is preferably 0.9 to 1.1mm, and more preferably 1.0 mm. In the invention, the volatilization temperature is preferably room temperature, and more preferably 20-25 ℃; the time is preferably 22 to 26 hours, and more preferably 24 to 25 hours. In the present invention, the volatilization is preferably carried out in a fume hood. In the invention, the drying temperature is preferably 55-62 ℃, and more preferably 58-60 ℃; the gold is preferably 10 to 14 hours, and more preferably 12 to 13 hours.
In the present invention, the drying preferably further comprises peeling the film-formed product from the mold. In the present invention, the peeling is preferably peeling.
The invention also provides the application of the degradable preservative film in the technical scheme or the degradable preservative film prepared by the preparation method in the technical scheme in preserving packaged edible fungi. In the present invention, the edible fungi preferably include agaricus bisporus, flammulina velutipes or pleurotus eryngii, and more preferably, agaricus bisporus. When the degradable preservative film is used for packaging, the water content of the edible fungi is preferably 73-95%, and more preferably 89-91%. The temperature for packaging and storing the edible fungi by using the degradable preservative film is preferably 3-5 ℃, and more preferably 4 ℃; the time is preferably 12 to 18 days, and more preferably 15 days.
In order to further illustrate the present invention, the following embodiments are described in detail, but they should not be construed as limiting the scope of the present invention.
Example 1
Dissolving 0.50g of chitosan (2.61mmol) and 1.06g of 1-hydroxybenzotriazole (7.83mmol) (stirring at 600r/min for 20h) in 50mL of 2% volume acetic acid aqueous solution to obtain chitosan solution;
0.61712g caffeic acid (7.83mmol) was dissolved (37kHz ultrasonic 20min) in 2mL absolute ethanol to obtain caffeic acid ethanol solution; dissolving 1.51g of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (37kHz ultrasonic for 20min) in 2mL of absolute ethanol to obtain an ethanol solution of 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride; dropwise adding the caffeic acid ethanol solution and the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution into the chitosan solution at a dropwise adding rate of 60 drops/min, and carrying out coupling reaction for 24 hours under the condition of keeping out of the sun (wrapping the reactor by tin foil paper); centrifuging a product of the coupling reaction at 10000r/min for 15min, and taking supernatant; adding 2mL of 11mol/L hydrochloric acid solution, mixing, and dialyzing (the aperture of a dialysis bag for dialysis is 14000Da) for 72h (changing water every 8 h); freeze-drying dialyzate obtained by dialysis for 54h to obtain a chitosan-caffeic acid graft copolymer which is marked as CA-g-CS;
dissolving 0.1g of chitosan-caffeic acid graft copolymer (ultrasonic treatment at 37kHz for 30min) in 10mL of ultrapure water to obtain a copolymer solution; dissolving 0.5g of polyethylene glycol with molecular weight of 8000 (600r/min magnetic stirring for 30min) in 25mL of ultrapure water to obtain polyethylene glycol solution; magnetically stirring the copolymer solution and the polyethylene glycol solution for 1h at 25 ℃ to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
magnetically stirring chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and drying undersize products for 2 hours at 60 ℃ to obtain a blend;
dissolving 0.6g of the blend (ultrasonic dispersion for 30min at 37kHz in an ice water bath) in 45mL of trichloromethane to obtain a blend solution;
dissolving 4.4g of polylactic acid (at 25 ℃, 600r/min) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the blending solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the coating solution into a stainless steel disc with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel disc in a fume hood for volatilizing for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃, and uncovering the film to obtain the degradable preservative film (the mass ratio of the polylactic acid to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 88:10: 2).
Example 2
A chitosan-caffeic acid graft copolymer was prepared according to the method of example 1;
dissolving 0.2g of chitosan-caffeic acid graft copolymer (ultrasonic treatment at 37kHz for 30min) in 20mL of ultrapure water to obtain a copolymer solution; dissolving 0.5g of polyethylene glycol with molecular weight of 8000 (600r/min magnetic stirring for 30min) in 25mL of ultrapure water to obtain polyethylene glycol solution; magnetically stirring the copolymer solution and the polyethylene glycol solution for 1h at 25 ℃ to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
magnetically stirring chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and drying undersize products for 2 hours at 60 ℃ to obtain a blend;
dissolving 0.7g of the blend (ultrasonic dispersion for 30min at 37kHz in an ice water bath) in 45mL of trichloromethane to obtain a blend solution;
dissolving 4.3g of polylactic acid (at 25 ℃, 600r/min) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the blending solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the coating solution into a stainless steel disc with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel disc in a fume hood for volatilizing for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃, and uncovering the film to obtain the degradable preservative film (the mass ratio of the polylactic acid to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 86:10: 4).
Example 3
A chitosan-caffeic acid graft copolymer was prepared according to the method of example 1;
dissolving 0.3g of chitosan-caffeic acid graft copolymer (ultrasonic treatment at 37kHz for 30min) in 30mL of ultrapure water to obtain a copolymer solution; dissolving 0.5g of polyethylene glycol with molecular weight of 8000 (600r/min magnetic stirring for 30min) in 25mL of ultrapure water to obtain polyethylene glycol solution; magnetically stirring the copolymer solution and the polyethylene glycol solution for 1h at 25 ℃ to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
magnetically stirring chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and drying undersize products for 2 hours at 60 ℃ to obtain a blend;
dissolving 0.8g of the blend (ultrasonic dispersion for 30min at 37kHz in an ice water bath) in 45mL of trichloromethane to obtain a blend solution;
dissolving 4.2g of polylactic acid (at 25 ℃, 600r/min) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the blending solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the film coating solution into a stainless steel disc with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel disc in a fume hood for volatilization for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃, and uncovering the film to obtain the degradable preservative film (the mass ratio of the polylactic acid, the polyethylene glycol and the chitosan-caffeic acid graft copolymer is 84:10:6), which is marked as CA-g-CS/PLA.
Example 4
A chitosan-caffeic acid graft copolymer was prepared according to the method of example 1;
dissolving 0.4g of chitosan-caffeic acid graft copolymer (ultrasonic treatment at 37kHz for 30min) in 40mL of ultrapure water to obtain a copolymer solution; dissolving 0.5g of polyethylene glycol with molecular weight of 8000 (600r/min magnetic stirring for 30min) in 25mL of ultrapure water to obtain polyethylene glycol solution; magnetically stirring the copolymer solution and the polyethylene glycol solution for 1h at 25 ℃ to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
magnetically stirring chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and drying undersize products for 2 hours at 60 ℃ to obtain a blend;
dissolving 0.9g of the blend (ultrasonic dispersion for 30min at 37kHz in an ice water bath) in 45mL of trichloromethane to obtain a blend solution;
dissolving 4.1g of polylactic acid (at 25 ℃, 600r/min) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the blending solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the coating solution into a stainless steel disc with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel disc in a fume hood for volatilizing for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃, and uncovering the film to obtain the degradable preservative film (the mass ratio of the polylactic acid to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 82:10: 8).
Comparative example 1
Dissolving 0.5g of polyethylene glycol with molecular weight of 8000 in 25mL of ultrapure water, and magnetically stirring for 1h at 25 ℃ to obtain a polyethylene glycol aqueous solution;
magnetically stirring polyethylene glycol aqueous solution at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and drying undersize products at 60 ℃ for 2h to obtain polyethylene glycol powder;
dissolving 0.5g of polyethylene glycol powder (ice water bath, 37kHz and ultrasonic treatment for 30min) in 35mL of chloroform to obtain a polyethylene glycol solution;
dissolving 4.5g of polylactic acid (at 25 ℃, 600r/min) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the polyethylene glycol solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the coating solution into a stainless steel plate with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel plate in a fume hood for volatilizing for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃ and uncovering the film to obtain the preservative film, wherein the mass ratio of polylactic acid to polyethylene glycol in the preservative film is 90: 10.
Comparative example 2
0.2g of chitosan (ultrasonic at 37kHz for 30min) is put into 10mL of ultrapure water to obtain a chitosan solution; dissolving 0.5g of polyethylene glycol with molecular weight of 8000 (600r/min magnetic stirring for 30min) in 25mL of ultrapure water to obtain polyethylene glycol solution; magnetically stirring chitosan solution and polyethylene glycol solution at 25 deg.C for 1 hr, magnetically stirring at 90 deg.C for water evaporation, drying at 60 deg.C for 12 hr until the solution is viscous; soaking the dried product in liquid nitrogen for 10min, and grinding in a mixed ball mill; sieving the ground product with a 150-mesh sieve, and taking undersize products to dry for 2 hours at 60 ℃ to obtain a chitosan and polyethylene glycol blend;
dissolving 0.7g of chitosan and polyethylene glycol blend (ice water bath 37kHz ultrasonic dispersion for 30min) in 45mL of trichloromethane to obtain a blending solution;
dissolving 4.3g of polylactic acid (600r/min stirring till dissolution) in 35mL of trichloromethane to obtain a polylactic acid solution;
magnetically stirring the blending solution and the polylactic acid solution for 10 hours, and then removing bubbles by ultrasonic treatment for 30min under the conditions of ice water bath and 37kHz to obtain a coating solution;
pouring the coating solution into a stainless steel plate with the thickness of 31cm multiplied by 15cm (the thickness of a wet film is 1mm), putting the stainless steel plate in a fume hood for volatilizing for 24h at the temperature of 25 ℃, drying for 12h at the temperature of 60 ℃ and uncovering the film to obtain the preservative film, wherein the mass ratio of polylactic acid, polyethylene glycol and chitosan in the preservative film is 86:10: 4).
Comparative example 3
The polyethylene preservative film sold in the market is taken as a comparative example.
The preservative film prepared in the embodiment 1 is marked as CA-g-CS/PLA, the preservative film prepared in the comparative example 1 is marked as PEG/PLA, the preservative film prepared in the comparative example 2 is marked as CS/PLA, and the preservative film prepared in the comparative example 3 is marked as PE.
The water vapor transmission rate and the oxygen transmission rate of the wrap films prepared in example 1 and comparative examples 1 to 3 were measured as follows, and the results are shown in table 1.
The method for detecting the water vapor transmission rate comprises the following steps: the water vapor transmission rate of the preservative film is detected according to GB 1037-
Figure BDA0003105441270000141
The water vapor permeability of the wrap film was measured by a TSY-T3 type moisture permeability tester at a temperature of 38. + -. 0.1 ℃ and a relative humidity of 90. + -. 2%. The test area is 33cm2Each group tested 3 samples and the results averaged.
The method for detecting the oxygen transmission rate comprises the following steps: the oxygen transmission rate of the preservative film is detected according to GB/T1038-108mm square, and the oxygen permeability of the film sample is tested and characterized by using an OX2/231 type oxygen permeability tester in the environment with the temperature of 23 ℃ and the relative humidity of (50 +/-5)%. The test area is 50cm 23 samples were made per group and the results averaged.
TABLE 1 Water vapor Transmission Rate and oxygen Transmission Rate of cling films prepared in example 1 and comparative examples 1-3
Figure BDA0003105441270000151
As can be seen from the data in table 1, the degradable preservative film prepared in example 1 has a large oxygen permeability, and due to the vigorous respiration of agaricus bisporus, the oxygen consumption in the packaging bag is fast, and the large oxygen permeability, the oxygen concentration in the packaging bag can be effectively adjusted, and the harm of anaerobic respiration, alcoholism and the like of fruits and vegetables can be prevented; the degradable preservative film prepared in the embodiment 1 has a high water vapor transmission rate, so that unnecessary water can be effectively diffused, and phenomena of fruit and vegetable rot, microorganism breeding and the like caused by condensation are prevented.
The degradation rates of the wrap films of example 1 and comparative example 2 were measured as follows, and the results are shown in Table 2.
Cutting the preservative film into 10 x 35mm2Drying the rectangle at 60 ℃ to constant weight; placing the preservative film into a 10mL sample bottle, and recording the initial mass m of the film0Adding degradation liquid (the degradation liquid is hydrochloric acid water solution with the concentration of 0mol/L, 0.1mol/L, 0.2mol/L and 0.5mol/L or sodium hydroxide water solution with the concentration of 0.1mol/L, 0.2mol/L and 0.5 mol/L) and then putting the mixture into a constant temperature oscillation box at 65 ℃; taking out the preservative film after a period of time, rinsing the preservative film for three times by using deionized water, drying the preservative film at 60 ℃ to constant weight, and weighing the preservative film and recording the mass as mNEach sample was measured 3 times in parallel and the sample degradation rate was calculated according to the following formula:
Figure BDA0003105441270000152
because the degradation medium is gradually consumed in the degradation process, in order to avoid the medium concentration from being greatly changed in the experiment process, the degradation liquid is replaced every 24 hours in the experiment.
Table 2 degradation rates of the cling films of example 1 and comparative example 2
Figure BDA0003105441270000153
Figure BDA0003105441270000161
The degradation rate of the degraded preservative film of example 1 in table 2 in the hydrochloric acid degradation solution is plotted as shown in (a) of fig. 1; a graph is drawn on the degradation rate of the preservative film of comparative example 2 in table 2 in a hydrochloric acid degradation solution, as shown in (b) of fig. 1; the degradation rate of the degraded preservative film of example 1 in table 2 in the sodium hydroxide degradation solution is plotted as shown in (c) of fig. 1; the degradation rate of the wrap film of comparative example 2 in table 2 in the sodium hydroxide degradation solution was plotted as shown in (d) of fig. 1. It can be known from the table 2 and the figure 1 that the degradable preservative film prepared in the example 1 has a high degradation rate in both the hydrochloric acid degradation solution and the sodium hydroxide degradation solution.
The wrap films of example 1, comparative example 2 and comparative example 3 were tested for freshness effect as follows.
Taking the agaricus bisporus as a test object, precooling purchased fresh agaricus bisporus for 24 hours at 4 ℃, and selecting samples with consistent size and maturity and without parachute opening, plant diseases and insect pests and mechanical damage. The agaricus bisporus is randomly divided into three groups, the agaricus bisporus is respectively placed into disposable fresh trays (polypropylene materials, 18cm multiplied by 11cm), three preservative films are respectively used for packaging, the packaging specification is 120 g/tray, each group of agaricus bisporus is packaged for 15 times and is used for storing samples of 3d, 6d, 9d, 12d and 15d for detection, and the test is repeated for 3 times each time. And (3) putting the agaricus bisporus subjected to different packaging treatments into a constant-temperature constant-humidity box with the relative humidity of 90% at 4 ℃ for 15 days for storage, and taking the agaricus bisporus umbrella part every 3 days for analysis and detection.
(1) Color difference value
The color of the surface of the pileus of the agaricus bisporus fruiting body was measured using a precision color difference meter, and the results thereof are shown in Table 3. At three equidistant points per mushroom cap, L (light/dark), a (red/green), b (yellow/blue) were measured and compared to the color value L of an ideal agaricus bisporusIdeal for＝97，a*Ideal for＝-2，b*Ideal forThe comparison is made at 0, reflecting the total colour difference change of the agaricus bisporus by Δ E.
Figure BDA0003105441270000171
In the formula: Δ E is the degree of overall color change compared to the color value of an ideal mushroom.
The browning index is calculated according to the following formula:
Figure BDA0003105441270000172
Figure BDA0003105441270000173
in the formula: BI is the brown color purity of the agaricus bisporus pileus to indicate the browning degree.
TABLE 3 color difference values after keeping fresh of Agaricus bisporus by the preservative films of example 1 and comparative examples 2 and 3
Figure BDA0003105441270000174
Figure BDA0003105441270000181
Plotting the data in the table, as shown in fig. 2, wherein (e) is a comparison plot of L ×; (f) comparative plot for Δ E; (g) is a comparative graph of BI. It can be known from the combination of the table 3 and the figure 2 that the preservative film in the example 1 can effectively delay the browning of the mushroom during the storage period after the picking of the agaricus bisporus.
(2) Headspace gas composition: extracting gas in Agaricus bisporus packaging bags with different storage time as sample to be tested, and analyzing with oxygen analyzer (model: OXYBABY M + O)2/CO2) The relative concentrations of oxygen and carbon dioxide in the gas samples were determined and analyzed, and the results are shown in Table 4.
TABLE 4 compositions of headspace air for freshness preservation using the wrap of example 1 and comparative examples 2 and 3
Figure BDA0003105441270000182
Plotting the data in Table 4, as shown in FIG. 3, where (m) is a plot of oxygen concentration versus time; (n) is a comparative plot of carbon dioxide concentration.
In the invention, the good barrier property of the degradable preservative film enables the preservative film to become an air-conditioned package (EMAP), and the gas components in the package are regulated through the selective permeability of the film to gas and fruit and vegetable respiration, so that the dynamic balance is finally achieved, and the stable and appropriate atmosphere in the package is kept. However, discoloration of agaricus bisporus during storage is promoted when the carbon dioxide concentration is higher than 5%. As can be seen from Table 4 and FIG. 3, the concentration of carbon dioxide in the CA-g-CS/PLA and CS/PLA groups was about 3%, and the concentration of oxygen was about 18%, so that the good color and appearance of Agaricus bisporus were maintained, and stress phenomena such as alcoholism caused by anaerobic respiration were avoided.
(3) Hardness: the hardness of the agaricus bisporus is measured by a TA-XT2 texture analyzer, and the measurement parameters are as follows: using a P6 probe, the probe preparation rate was 2.00mm/s, the measurement rate was 1.00mm/s, the probe measurement rate was 5.00mm/s, the measurement depth was 5.00mm, and the minimum force was 0.005kg, and the measurement was performed by taking 10 mushroom bodies each time, and the maximum force during the pressing was taken as the hardness, and the results are shown in Table 5.
TABLE 5 hardness of Agaricus bisporus preserved with the preservative film of example 1 and comparative examples 2 and 3
Figure BDA0003105441270000191
Hardness versus curve is plotted according to table 5, as shown in fig. 4. As can be seen from table 5 and fig. 4, the hardness of agaricus bisporus showed a tendency of increasing first and then decreasing during the entire storage period. The after-harvest ripening of agaricus bisporus is the main reason for the hardness increase of agaricus bisporus. Hardness of agaricus bisporus decreased gradually in all experimental groups from the 3 rd day of storage. After the sixth day, the hardness of the CA-g-CS/PLA group was higher than that of the PE group and the CS/PLA group, probably due to the increased proliferation of microorganisms due to the higher relative humidity in the PE group and the CS/PLA group. Compared with the PE group and the CS/PLA group, the CA-g-CS/PLA film package can obviously delay the reduction of the hardness of the agaricus bisporus.
(4) And (3) respiratory rate determination:
blank group: 10mL of NaOH standard solution (0.4mol/L) was transferred to a petri dish, which was placed on the bottom of the desiccator for a while. Transferring the alkali liquor into a beaker, repeatedly washing with distilled water to completely transfer the alkali liquor into the beaker, adding 2 drops of phenolphthalein, titrating by using an oxalic acid standard solution with the concentration of 0.2mol/L until the red color completely disappears, and recording the using amount of the oxalic acid standard solution.
Experimental groups: 120g of agaricus bisporus packaged by using a preservative film is used as a test object. 10mL of NaOH standard solution (0.4mol/L) was transferred to a petri dish, and the petri dish was placed on the bottom of the desiccator. Placing the clapboard, placing the agaricus bisporus in a dryer, sealing the dryer, breathing for a period of time, and taking out the culture dish. Transferring the alkali liquor into a beaker, repeatedly washing with distilled water to completely transfer the alkali liquor into the beaker, adding 2 drops of phenolphthalein, titrating by using an oxalic acid standard solution with the concentration of 0.2mol/L until the red color completely disappears, and recording the dosage of the L oxalic acid standard solution. The respiration rate of Agaricus bisporus was calculated according to the following formula, and the results are shown in Table 6.
Figure BDA0003105441270000201
In the formula: v1The volume of the oxalic acid standard solution used for the blank group, mL; v2The volume of oxalic acid standard solution used for the sample set, mL; c is the concentration of the oxalic acid standard solution, mol/L; w is the mass of the sampleKg; t is the experimental time, h.
TABLE 6 respiration Rate of Agaricus bisporus preserved with the preservative film of example 1 and comparative examples 2 and 3
Figure BDA0003105441270000202
The respiration rate versus graph is plotted according to table 6, as shown in fig. 5. After the harvest, the agaricus bisporus has vigorous respiration and transpiration, and as can be seen from table 6 and fig. 5, the agaricus bisporus of the PE group, the CS/PLA group and the CA-g-CS/PLA group have the highest respiration rate on day 6. The respiration rate of the PE group remained at a higher level from day 3 onwards, probably because a high respiration rate accelerates the consumption of nutrients and initiates spoilage of the mushrooms. The CS/PLA film package group also has a higher respiration rate than the CA-g-CS/PLA film package group, which accelerates the consumption of nutrients, resulting in spoilage of Agaricus bisporus.
Fig. 6 shows the actual picture of the agaricus bisporus after being preserved for 0 day, 3 days, 6 days, 9 days, 12 days and 15 days by the preservative films of example 1 and comparative examples 2 and 3. As can be seen from a packaging diagram, the phenomenon of condensation occurs in the PE film, and the phenomenon of condensation does not occur in CA-g-CS/PLA and CS/PLA, and the degradable preservative film prepared by the invention is verified to have good water vapor transmission rate. The appearance of each treated group of agaricus bisporus did not change significantly after 3 days of freshness preservation. From the 6 th day of preservation, the surface damage and the color of the agaricus bisporus among the groups begin to be different, the yellowness of the agaricus bisporus of the PE group is obviously increased, and the surface damage is increased. On the 9 th day, browning degree of Agaricus bisporus of PE group is increased, large brown spots appear, surface of CS/PLA group turns yellow, a small amount of brown spots appear, and CA-g-CS/PLA group appearance is still good. On day 12, the whole Agaricus bisporus of PE group was brown and incomplete in shape, and the CS/PLA group showed a large number of brown spots and the CA-g-CS/PLA group had good appearance. And on the 15 th day, browning is more serious in the CS/PLA group, browning is carried out in the CA-g-CS/PLA group, and in the whole storage period, the tissues of the PE group are immersed in water in the later storage period, while browning is carried out in the CA-g-CS/PLA and the CS/PLA but the tissues are not immersed in water. The browning degree of the agaricus bisporus packaged by the CA-g-CS/PLA is minimum, which shows that the CA-g-CS/PLA film can effectively delay the browning of the agaricus bisporus during storage and maintain good appearance quality.
The degradable preservative film provided by the invention has good moisture permeability, so that carbon dioxide and water generated by respiration of edible fungi during storage are discharged in time, and relatively stable oxygen, carbon dioxide content and relative humidity are finally formed, thereby being beneficial to prolonging the shelf life of the edible fungi and realizing long-term preservation of the edible fungi.
Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and the embodiments are within the scope of the present invention.

Claims (9)

1. A degradable preservative film comprising a polylactic acid-based film, polyethylene glycol and a chitosan-caffeic acid graft copolymer contained in the polylactic acid-based film;
the mass ratio of the polylactic acid base film to the polyethylene glycol to the chitosan-caffeic acid graft copolymer is 82-88: 10: 2-8;
the preparation method of the chitosan-caffeic acid graft copolymer comprises the following steps:
dissolving chitosan and 1-hydroxybenzotriazole in an acetic acid aqueous solution to obtain a chitosan solution;
mixing caffeic acid ethanol solution, 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution and chitosan solution for coupling reaction to obtain the chitosan-caffeic acid graft copolymer;
the mass ratio of the chitosan to the 1-hydroxybenzotriazole is 0.5: 1.04-1.08; the volume concentration of the acetic acid aqueous solution is 1.8-2.2%; the volume ratio of the mass of the chitosan to the volume of the acetic acid aqueous solution is 0.5g: 48-52 mL;
the volume ratio of the mass of the caffeic acid to the volume of the ethanol is 0.6-0.63: 2 mL;
the volume ratio of the mass of the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride to the volume of the ethanol is 1.5-1.53: 2 mL;
the volume ratio of the caffeic acid ethanol solution to the 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride ethanol solution to the chitosan solution is 1:1:23 to 27.
2. The degradable plastic wrap of claim 1, wherein the thickness of the degradable plastic wrap is 0.0146-0.0188 mm.
3. The method for preparing the degradable preservative film according to claim 1 or 2, comprising the steps of:
dissolving a chitosan-caffeic acid graft copolymer and polyethylene glycol blend in chloroform to obtain a blended solution;
dissolving polylactic acid in trichloromethane to obtain a polylactic acid solution;
adding the blending solution into a polylactic acid solution to obtain a coating solution;
and forming a film by using the coating liquid to obtain the degradable preservative film.
4. The method according to claim 3, wherein the particle diameters of the chitosan-caffeic acid graft copolymer and the polyethylene glycol are independently 106 μm or less.
5. The method according to claim 3, wherein the chitosan-caffeic acid graft copolymer and the polyethylene glycol before being dissolved further comprises: preparing a chitosan-caffeic acid graft copolymer and polyethylene glycol to obtain a blend of the chitosan-caffeic acid graft copolymer and the polyethylene glycol;
the preparation method of the blend of the chitosan-caffeic acid graft copolymer and polyethylene glycol comprises the following steps:
mixing the chitosan-caffeic acid graft copolymer, polyethylene glycol and water to obtain a chitosan-caffeic acid graft copolymer and polyethylene glycol aqueous solution;
and drying the chitosan-caffeic acid graft copolymer and the aqueous solution of polyethylene glycol, and then sequentially grinding and sieving to obtain the blend.
6. The preparation method according to claim 3, wherein the total mass concentration of the chitosan-caffeic acid graft copolymer and the polyethylene glycol in the blending solution is 0.01-0.02 g/mL.
7. The preparation method according to claim 3, wherein the mass concentration of the polylactic acid in the polylactic acid solution is 0.11-0.13 g/mL.
8. The production method according to claim 3, wherein the wet film thickness obtained by the film formation is 0.9 to 1.1 mm.
9. The degradable preservative film according to claim 1 or 2 or the degradable preservative film prepared by the preparation method according to any one of claims 3 to 8 is applied to preservation of packaged edible fungi.
CN202110635276.7A 2021-06-08 2021-06-08 Degradable preservative film and preparation method and application thereof Active CN113354930B (en)

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