CN112544694A - Preservative paper for curing picked kiwi fruits and curing method of picked kiwi fruits - Google Patents
Preservative paper for curing picked kiwi fruits and curing method of picked kiwi fruits Download PDFInfo
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- CN112544694A CN112544694A CN202011110405.2A CN202011110405A CN112544694A CN 112544694 A CN112544694 A CN 112544694A CN 202011110405 A CN202011110405 A CN 202011110405A CN 112544694 A CN112544694 A CN 112544694A
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- Prior art keywords
- paper
- polylactic acid
- preservative
- kiwi fruits
- curing
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Links
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Images
Classifications
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/14—Preserving or ripening with chemicals not covered by groups A23B7/08 or A23B7/10
- A23B7/144—Preserving or ripening with chemicals not covered by groups A23B7/08 or A23B7/10 in the form of gases, e.g. fumigation; Compositions or apparatus therefor
- A23B7/152—Preserving or ripening with chemicals not covered by groups A23B7/08 or A23B7/10 in the form of gases, e.g. fumigation; Compositions or apparatus therefor in a controlled atmosphere comprising other gases in addition to CO2, N2, O2 or H2O ; Elimination of such other gases
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/14—Preserving or ripening with chemicals not covered by groups A23B7/08 or A23B7/10
- A23B7/153—Preserving or ripening with chemicals not covered by groups A23B7/08 or A23B7/10 in the form of liquids or solids
- A23B7/154—Organic compounds; Microorganisms; Enzymes
-
- 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
- B65D65/40—Applications of laminates for particular packaging purposes
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/03—Non-macromolecular organic compounds
- D21H17/05—Non-macromolecular organic compounds containing elements other than carbon and hydrogen only
- D21H17/14—Carboxylic acids; Derivatives thereof
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/10—Coatings without pigments
- D21H19/12—Coatings without pigments applied as a solution using water as the only solvent, e.g. in the presence of acid or alkaline compounds
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/10—Coatings without pigments
- D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
- D21H19/24—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
- D21H19/28—Polyesters
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/10—Coatings without pigments
- D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
- D21H19/34—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising cellulose or derivatives thereof
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/66—Coatings characterised by a special visual effect, e.g. patterned, textured
- D21H19/70—Coatings characterised by a special visual effect, e.g. patterned, textured with internal voids, e.g. bubble coatings
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/80—Paper comprising more than one coating
- D21H19/82—Paper comprising more than one coating superposed
- D21H19/824—Paper comprising more than one coating superposed two superposed coatings, both being non-pigmented
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
- D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
- D21H23/22—Addition to the formed paper
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
- D21H25/04—Physical treatment, e.g. heating, irradiating
- D21H25/06—Physical treatment, e.g. heating, irradiating of impregnated or coated paper
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
- D21H27/30—Multi-ply
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23V—INDEXING SCHEME RELATING TO FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES AND LACTIC OR PROPIONIC ACID BACTERIA USED IN FOODSTUFFS OR FOOD PREPARATION
- A23V2002/00—Food compositions, function of food ingredients or processes for food or foodstuffs
-
- 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 relates to fruit and vegetable processing and storage, and discloses preservative paper for curing picked kiwi fruits and a method for curing picked kiwi fruits, wherein the preparation method of the preservative paper comprises the following steps: 1) taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper, and curing to obtain double-layer composite paper with a polylactic acid foam layer; 2) dipping the double-layer composite paper in an ascorbic acid solution, taking out the dipped double-layer composite paper and drying the dipped double-layer composite paper; 3) dissolving sodium alginate in the oxidized starch solution to obtain a coating liquid; 4) and (3) uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper obtained in the step 2) to form a coating layer, and fully drying to obtain the preservative paper. The preservative paper is specially used for artificial ripening of the kiwi fruits, has short ripening cycle and long shelf life after ripening, and can reduce the damage of the kiwi fruits in the conveying and storing processes. The curing method is simple to operate and low in cost.
Description
Technical Field
The invention relates to fruit and vegetable processing and storage, in particular to preservative paper for curing picked kiwi fruits and a method for curing picked kiwi fruits.
Background
Kiwi is one of the most important emerging fruits in the world, and the main production places of the Kiwi fruit cover China, Italy, New Zealand and other countries. The kiwi fruit not only can be directly eaten, but also can be processed into fruit juice, preserved fruit, jam, can and the like, and has rich nutritional value and good medicinal value. The kiwi fruit contains a large amount of sugar, protein, dietary fiber, polyphenol, carotenoid and a plurality of mineral substances and vitamin (Vc), especially the content of Vc is particularly high (120-428 mg/100g), which far exceeds that of apples, pears and oranges, so the kiwi fruit is called 'king in fruit' and 'treasure in fruit'. In addition, the kiwi fruit has high medicinal value, and the fresh kiwi fruit and the kiwi fruit juice are widely used in clinical tests by some medical and health units, and have certain auxiliary treatment effect on digestive tract diseases, hypertension, hepatitis and other diseases. Because of the advantages, the kiwi fruits are widely popular with consumers and have high commercial value.
Kiwi fruit is a typical climacteric fruit, and has obvious physiological after-ripening process under the influence of the physiological characteristics of the Kiwi fruit, and the Kiwi fruit has high hardness and poor flavor after storage, is not suitable for eating and is usually subjected to ripening treatment. In recent years, various artificial ripening acceleration and fresh-keeping technical methods are developed, such as solid adsorption ripening acceleration agent, low-temperature refrigeration, coating preservation, modified atmosphere storage, biological preservation and the like. But different methods have disadvantages, such as short shelf life of the kiwi fruits treated by the solid adsorption ripener at normal temperature, only 2-3 days; the low-temperature fresh-keeping method has higher energy consumption; the film coating preservation method has poor preservation effect on fruits and vegetables with hairy surfaces; the air-conditioned storage method has high requirements on equipment and the like; the biological fresh-keeping method has poor universality, namely different modes are adopted according to different species, and long-time verification is required for whether modified species involved in the genetic engineering fresh-keeping technology are harmless to human bodies.
In conclusion, the storage, transportation and preservation of kiwi fruits are common problems faced by relevant practitioners and technologists, and a method capable of properly accelerating ripening and maintaining good quality of kiwi fruits during storage is urgently needed in the field.
Disclosure of Invention
In order to solve the problems of short shelf life of kiwi fruits after artificial ripening, poor stability of ripening effect, poor preservation effect of kiwi fruits by coating preservation, high cost of low temperature and air conditioning and the like in the prior art, the invention provides preservative paper for ripening picked kiwi fruits and a ripening method of kiwi fruits. The curing method is simple to operate and low in cost.
The specific technical scheme of the invention is as follows:
in a first aspect, the invention provides preservative paper for curing picked kiwi fruits, and the preparation method comprises the following steps:
1) taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper, and curing to obtain the double-layer composite paper with the polylactic acid foam layer.
2) And (3) soaking the double-layer composite paper in an ascorbic acid solution, taking out after soaking, and drying.
3) And dissolving sodium alginate in the oxidized starch solution to obtain the coating liquid.
4) And (3) uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper obtained in the step 2) to form a coating layer, and fully drying to obtain the preservative paper.
The technical effects of the preservative paper of the invention are as follows:
(1) according to the invention, the polylactic acid foam layer is applied to one side of the preservative paper, and the polylactic acid foam layer has the following functions: firstly, the polylactic acid foam layer plays a role in buffering protection, so that the probability of physical damage caused by collision and extrusion in the storage and transportation processes is greatly reduced; secondly, after the kiwi fruits are wrapped by the preservative paper, an ethylene-rich microenvironment can be formed between the surfaces of the kiwi fruits and the preservative paper in the ripening process of the kiwi fruits, so that the ripening period is shortened (about 7 days). To facilitate this effect, the present invention intentionally applies a polylactic acid foam layer followed by a coating layer, because we have found that the polylactic acid foam layer, due to its rich channel structure, absorbs the released ethylene and is not conducive to forming an ethylene-rich microenvironment. According to the application sequence of the invention, a coating layer can be formed on the polylactic acid foam layer, and the sticky substances in the coating layer can play a role in closing pores of the channels, so that the ethylene is prevented from being adsorbed by the polylactic acid foam layer, and meanwhile, the function of blocking the external water and gas from entering is also played. And the polylactic acid foam layer has rich pore channel structures, can be used as a good adsorption carrier of ascorbic acid, and improves the load rate.
(2) The preservative paper is loaded with oxidized starch, sodium alginate and ascorbic acid, wherein the sodium alginate and the ascorbic acid can effectively reduce the weight loss rate and the rotting rate of the kiwi fruits during storage and maintain good quality; the oxidized starch and the sodium alginate have high viscosity after meeting water, and can form a coating layer with good barrier property on the surface of the polylactic acid foam layer to prevent ethylene from being adsorbed and prevent external water and gas from entering.
(3) The preservative paper has simple and convenient use method and low preservation cost: the size of the preservative paper can be cut and customized according to actual conditions, the preservative form only needs to wrap the kiwi fruits, and common workers can quickly master the using method.
Preferably, in the step 1), the thickness of the base paper is 0.175-0.2mm, and the thickness of the polylactic acid foam layer is 0.15-0.2 mm.
Since the polylactic acid foam layer of the present invention is required to play a role of cushioning protection, its thickness is required to be thick.
Preferably, in the step 1), the aging condition is 40-50 ℃, and the standing is 20-40 min.
Preferably, in step 1), the preparation method of the uncured polylactic acid foam material comprises the following steps:
A) adding tea polyphenols into water, heating to 50-60 deg.C under stirring, adjusting pH of the obtained solution to 1-2, maintaining pH for reaction for 4-6h, and continuously adding tea polyphenols during reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Tea polyphenol has been widely used as a preservative, and in the prior art, the tea polyphenol is blended with polylactic acid and the like to prepare a preservative film. However, this solution has the disadvantages: the tea polyphenol and the polylactic acid are compounded through later-stage physical blending, and due to the property difference of the tea polyphenol and the polylactic acid, the tea polyphenol is easy to separate out at the later stage, so that the preservation effect of the obtained preservation material is influenced and the stability is poor. Therefore, the fresh-keeping substance and the lactic acid are subjected to dehydration polycondensation together, and the fresh-keeping substance and the lactic acid are compounded in the polylactic acid in a molecular chain block form, so that the fresh-keeping substance is chemically combined, has better stability compared with physical blending, and is not easy to separate out in the later period.
However, the molecular structural characteristics of tea polyphenol make it unable to participate in the dehydration condensation of lactic acid (only contains a large amount of phenolic hydroxyl groups and lacks carboxyl groups). Therefore, in the step A), tea polyphenol is firstly subjected to acidolysis under a specific pH condition (pH =1-2, and the tea polyphenol has strong acid resistance), ester bonds in the structural formula are decomposed under strong acidity to form carboxyl, and therefore, a hydrolysate of the tea polyphenol contains substances simultaneously having hydroxyl and carboxyl, and has the capacity of participating in lactic acid dehydration polycondensation. It should be noted that since the above reaction is a reversible reaction, it is necessary to continuously add tea polyphenol during the reaction to make the reaction proceed in a favorable direction.
B) Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 65-75 ℃, and carrying out vacuum reaction for 2-4 h; adding a tea polyphenol hydrolysate, heating to the temperature of 120-.
In the step B), lactic acid and a hydrolysate of tea polyphenol are subjected to dehydration and polycondensation to obtain the hybrid polylactic acid particles. It should be noted that the tea polyphenol hydrolysate needs to be added after the lactic acid prepolymer is formed, because the early addition of the tea polyphenol hydrolysate can easily cause premature termination of the polycondensation reaction (the reaction activity of the tea polyphenol hydrolysate is lower than that of the lactic acid monomer, and the early participation of the tea polyphenol hydrolysate in the reaction can play a role of an end-capping agent), thereby affecting the molecular weight of the polymer.
C) And mixing the hybrid polylactic acid particles and the nano cellulose according to the mass ratio of (97: 3) - (99: 1), adding the mixture into an injection molding machine, heating, pressurizing and melting, introducing carbon dioxide into the injection molding machine to fully blend the mixture with the hybrid polylactic acid melt, and extruding to obtain the uncured polylactic acid foam material.
In step C), the invention carries out foaming treatment on the hybrid polylactic acid. In the foaming process, the nanocellulose plays a role in heterogeneous nucleation, and molecular chains of the hybrid polylactic acid can be gathered and regularly arranged, so that the crystallization rate can be improved, and the foaming efficiency can be accelerated. Carbon dioxide is used as a foaming medium to be blended with the polymer, the high pressure is instantly converted into normal pressure after extrusion, and gas escapes from the polymer under the pressure difference to form a pore channel.
Preferably, in step B), the addition amount of the tea polyphenol hydrolysate is 0.1-0.5wt% of lactic acid.
The research of the invention group finds that the content of the tea polyphenol hydrolysate in the hybrid polylactic acid is very important, and the content directly determines the molecular chain hybridization degree of the hybrid polylactic acid, thereby having a profound influence on the processing performance of the polylactic acid. If the hybridization process is too high, dehydration and polycondensation are difficult in the synthesis process of the polylactic acid, and the rheological property and the foamability of the obtained hybrid polylactic acid are affected; on the contrary, if the hybridization degree is lower, the obtained hybrid polylactic acid has no obvious fresh-keeping effect.
Preferably, in the step C), the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 100-500 mL/kg; wherein the introduction process of the carbon dioxide comprises the following steps: firstly, 70-80% of carbon dioxide is introduced at the rate of 30-40mL/min, and then the rest carbon dioxide is introduced at the rate of 10-20 mL/min.
The introduction amount of carbon dioxide directly determines the foaming effect of the hybrid polylactic acid. In addition, in order to achieve a better foaming effect, the team of the invention divides the introduction of carbon dioxide into two stages, namely high-flow foaming and low-flow foaming. The process has the advantages that: introducing most of carbon dioxide at a high flow rate in the first stage, wherein the continuous gas flow is cracked and wrapped by the polymer melt in the mixing process to form large-size bubbles; and then, the residual carbon dioxide is introduced at a small flow rate in the second stage, and bubbles formed in the polymer melt after the carbon dioxide with the small flow rate is introduced have small sizes and can be distributed among large-size bubbles in the mixing process, so that the porosity of the polylactic acid foam material is increased, the buffer protection effect of the polylactic acid foam material is improved, and the weight of the preservative paper is reduced.
Preferably, in the step 2), the concentration of the ascorbic acid solution is 0.2-0.6wt%, the dipping time is 3-7s, and the dipping amount is 0.5-1.0 g/m2。
Preferably, in the step 3), the concentration of the oxidized starch solution is 10-20 wt%; the concentration of sodium alginate in the coating liquid is 0.5-1.5 wt%.
Preferably, in step 4), the coating weight is controlled to be 9.5-10.5 g/m2。
In a second aspect, the invention provides a method for ripening kiwi fruits after picking, which comprises the steps of wrapping the picked kiwi fruits by using the preservative paper of the invention, and then storing the kiwi fruits to promote ripening of the kiwi fruits.
The preservative paper has simple and convenient use method and low preservation cost: the size of the preservative paper can be cut and customized according to actual conditions, the preservative form only needs to wrap the kiwi fruits, and common workers can quickly master the using method.
Compared with the prior art, the invention has the beneficial effects that:
(1) the preservative paper is specially used for artificial ripening of the kiwi fruits, an ethylene-rich microenvironment can be formed around the kiwi fruits after the kiwi fruits are wrapped, and the ripening cycle is short (about 7 days).
(2) The preservative paper contains preservative substances, and has long shelf life after ripening.
(3) The preservative paper contains the polylactic acid foam layer, so that the damage of the kiwi fruits in the conveying and storing processes can be reduced.
(4) The method is simple and convenient, and has low preservation cost: the size of the preservative paper can be cut and customized according to actual conditions, the preservative form only needs to wrap the kiwi fruits, and common workers can quickly master the using method.
Drawings
FIG. 1 is a graph of data analysis of the hardness of the ripened kiwi fruits of different groups;
FIG. 2 is a graph of relative conductivity data analysis of postharvest ripening of different groups of kiwifruits;
FIG. 3 is a graph of data analysis of solid-acid ratio of kiwi fruit aged after picking in different groups.
Detailed Description
The present invention will be further described with reference to the following examples.
General examples
A preservative paper for curing picked kiwi fruits is prepared by the following steps:
1) taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.175-0.2 mm), standing and curing at 40-50 ℃ for 20-40min, and curing to obtain the double-layer composite paper with a polylactic acid foam layer (0.15-0.2 mm).
2) Soaking the double-layer composite paper in 0.2-0.6wt% ascorbic acid solution for 3-7s, taking out after soaking, and drying. The impregnation amount is 0.5-1.0 g/m2。
3) Dissolving sodium alginate in 10-20wt% of oxidized starch solution to obtain a coating liquid; the concentration of sodium alginate in the coating liquid is 0.5-1.5 wt%.
4) Uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper obtained in the step 2) to form a coating layer, wherein the coating amount is controlled to be 9.5-10.5 g/m2And fully drying to obtain the preservative paper.
Preferably, the preparation method of the uncured polylactic acid foam material comprises the following steps:
A) adding tea polyphenols into water, heating to 50-60 deg.C under stirring, adjusting pH of the obtained solution to 1-2, maintaining pH for reaction for 4-6h, and continuously adding tea polyphenols during reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
B) Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 65-75 ℃, and carrying out vacuum reaction for 2-4 h; adding 0.1-0.5wt% of tea polyphenol hydrolysate of lactic acid, heating to 120-140 ℃ for dehydration polycondensation reaction for 3-5h, further heating to 190-210 ℃ for further reaction for 2-4h, draining, cooling, separating the product, and pelletizing to obtain the hybrid polylactic acid particles.
C) Mixing hybrid polylactic acid particles and nanocellulose according to a mass ratio of (97: 3) - (99: 1), adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 100-500 mL/kg; the introduction process of the carbon dioxide comprises the following steps: firstly, 70-80% of carbon dioxide is introduced at the rate of 30-40mL/min, and then the rest carbon dioxide is introduced at the rate of 10-20 mL/min. After extrusion, an uncured polylactic acid foam is obtained.
The invention relates to a ripening method of picked kiwi fruits, which comprises the steps of wrapping the picked kiwi fruits by using preservative paper (25 cm multiplied by 25 cm), and storing the kiwi fruits to promote the ripening of the kiwi fruits.
Example 1
A preservative paper for curing picked kiwi fruits is prepared by the following steps:
adding tea polyphenol into water, heating to 55 ℃ under the condition of stirring, adjusting the pH of the obtained solution to about 1.5, maintaining the pH for reaction for 5 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 70 ℃, and carrying out vacuum reaction for 3 hours; adding a tea polyphenol hydrolysate with the mass of 0.3wt% of lactic acid, heating to 130 ℃, performing dehydration and polycondensation reaction for 4 hours, further heating to 200 ℃, continuing the reaction for 3 hours, draining, cooling, separating the product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 98:2, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 300 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 75% of carbon dioxide is firstly introduced at the rate of 35mL/min, and then the rest carbon dioxide is introduced at the rate of 15mL/min, and the uncured polylactic acid foam material is obtained after extrusion.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.2 mm), standing and curing at 45 ℃ for 30min to obtain the double-layer composite paper with the polylactic acid foam layer (0.2 mm).
And (3) soaking the double-layer composite paper in 0.4wt% ascorbic acid solution for 5s, taking out after soaking, and drying. The impregnation amount was 0.75 g/m2。
Dissolving sodium alginate in 16wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1 wt%.
Uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper to form a coating layer, wherein the coating amount is controlled to be 10 g/m2And fully drying to obtain the preservative paper.
Example 2
A preservative paper for curing picked kiwi fruits is prepared by the following steps:
adding tea polyphenol into water, heating to 50 ℃ under the condition of stirring, adjusting the pH of the obtained solution to 1, maintaining the pH for reaction for 6 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 65 ℃ and carrying out vacuum reaction for 4 hours; adding a tea polyphenol hydrolysate with the mass of 0.1wt% of lactic acid, heating to 120 ℃, performing dehydration and polycondensation reaction for 5 hours, further heating to 190 ℃, continuing to react for 4 hours, draining, cooling, separating a product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 97:3, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 100 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 70% of the carbon dioxide was introduced at a rate of 30mL/min, and the remaining carbon dioxide was introduced at a rate of 10 mL/min. After extrusion, an uncured polylactic acid foam is obtained.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.175 mm), standing and curing at 40 ℃ for 40min to obtain the double-layer composite paper with the polylactic acid foam layer (0.15 mm).
And (3) soaking the double-layer composite paper in 0.2wt% ascorbic acid solution for 3s, taking out after soaking, and drying. The impregnation amount was 0.5 g/m2。
Dissolving sodium alginate in 10wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 0.5 wt%.
Uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper to form a coating layer, wherein the coating amount is controlled to be 9.5 g/m2And fully drying to obtain the preservative paper.
Example 3
A preservative paper for curing picked kiwi fruits is prepared by the following steps:
adding tea polyphenol into water, heating to 60 ℃ under the condition of stirring, adjusting the pH of the obtained solution to 2, maintaining the pH for reaction for 4 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 75 ℃, and carrying out vacuum reaction for 2 h; adding a tea polyphenol hydrolysate with the mass of 0.5wt% of lactic acid, heating to 140 ℃, performing dehydration and polycondensation reaction for 3h, further heating to 210 ℃, continuing the reaction for 2h, draining, cooling, separating the product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 99:1, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 500 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 80% of the carbon dioxide was introduced at a rate of 40mL/min, and the remainder was introduced at a rate of 20 mL/min. After extrusion, an uncured polylactic acid foam is obtained.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.18 mm), standing and curing at 50 ℃ for 20min to obtain the double-layer composite paper with the polylactic acid foam layer (0.18 mm).
Soaking the double-layer composite paper in 0.2-0.6wt% ascorbic acid solution for 7s, taking out after soaking, and drying. The impregnation amount is 0.5-1.0 g/m2。
Dissolving sodium alginate in 20wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1.5% by weight.
Uniformly coating the coating liquid on the polylactic acid foam layer of the paper to form a coating layer, wherein the coating amount is controlled to be 10.5 g/m2And fully drying to obtain the preservative paper.
Example 4
A preservative paper for curing picked kiwi fruits is prepared by the following steps:
adding tea polyphenol into water, heating to 55 ℃ under the condition of stirring, adjusting the pH of the obtained solution to 2, maintaining the pH for reaction for 5 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 75 ℃, and carrying out vacuum reaction for 2.5 h; adding a tea polyphenol hydrolysate with the mass of 0.2wt% of lactic acid, heating to 125 ℃, performing dehydration and polycondensation reaction for 4 hours, further heating to 200 ℃, continuing the reaction for 4 hours, draining, cooling, separating the product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 99:1, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 400 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 70% of the carbon dioxide was introduced at a rate of 30mL/min, and the remaining carbon dioxide was introduced at a rate of 10 mL/min. After extrusion, an uncured polylactic acid foam is obtained.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.2 mm), standing and curing at 40 ℃ for 30min to obtain the double-layer composite paper with the polylactic acid foam layer (0.15 mm).
And (3) soaking the double-layer composite paper in 0.3wt% ascorbic acid solution for 5s, taking out after soaking, and drying. The impregnation amount was 0.6 g/m2。
Dissolving sodium alginate in 15wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1 wt%.
Uniformly coating the coating liquid onA coating layer is formed on the surface of the paper where the polylactic acid foam layer is arranged, and the coating amount is controlled to be 10 g/m2And fully drying to obtain the preservative paper.
Comparative example 1 (different from example 1 in that no freshness-retaining substance was added)
The preparation method of the preservative paper comprises the following steps: taking base paper, uniformly applying uncured polylactic acid foam material (which is different from non-hybrid polylactic acid in example 1) on one surface of the base paper (0.2 mm), standing and curing at 45 ℃ for 30min to obtain the preservative paper with the polylactic acid foam layer (0.2 mm) after curing.
Comparative example 2 (different from example 1 in that tea polyphenol is compounded with polylactic acid in the form of physical blend)
The preparation method of the preservative paper comprises the following steps:
mixing polylactic acid particles (different from non-hybrid polylactic acid in example 1), tea polyphenol and nanocellulose according to the mass ratio of 97.8:0.2:2, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 300 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 75% of carbon dioxide is firstly introduced at the rate of 35mL/min, and then the rest carbon dioxide is introduced at the rate of 15mL/min, and the uncured polylactic acid foam material is obtained after extrusion.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.2 mm), standing and curing at 45 ℃ for 30min to obtain the double-layer composite paper with the polylactic acid foam layer (0.2 mm).
And (3) soaking the double-layer composite paper in 0.4wt% ascorbic acid solution for 5s, taking out after soaking, and drying. The impregnation amount was 0.75 g/m2。
Dissolving sodium alginate in 16wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1 wt%.
Uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper to form a coating layer, wherein the coating amount is controlled to be 10 g/m2After being fully dried, the product is obtainedThe preservative paper is characterized by being made of a paper.
Comparative example 3 (different from example 1 in that a coating layer was applied and then a polylactic acid foam layer was applied)
The preparation method of the preservative paper comprises the following steps:
dissolving sodium alginate in 16wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1 wt%.
Taking base paper, uniformly coating a coating solution on one surface of the base paper (0.2 mm) to form a coating layer, wherein the coating amount is controlled at 10 g/m2And fully drying.
Adding tea polyphenol into water, heating to 55 ℃ under the condition of stirring, adjusting the pH of the obtained solution to about 1.5, maintaining the pH for reaction for 5 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 70 ℃, and carrying out vacuum reaction for 3 hours; adding a tea polyphenol hydrolysate with the mass of 0.3wt% of lactic acid, heating to 130 ℃, performing dehydration and polycondensation reaction for 4 hours, further heating to 200 ℃, continuing the reaction for 3 hours, draining, cooling, separating the product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 98:2, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 300 mL/kg; the introduction process of the carbon dioxide comprises the following steps: 75% of carbon dioxide is firstly introduced at the rate of 35mL/min, and then the rest carbon dioxide is introduced at the rate of 15mL/min, and the uncured polylactic acid foam material is obtained after extrusion.
Uniformly applying uncured polylactic acid foam material on the coating layer of the preservative paper, standing and curing at 45 ℃ for 30min to form a polylactic acid foam layer (0.2 mm) after curing.
Soaking the preservative paper with the polylactic acid foam layer in 0.4wt% ascorbic acid solution for 5s, wherein the soaking amount is 0.75 g/m2And taking out after dipping and drying to obtain the preservative paper.
Comparative example 4 (differing from example 1 in that staged carbon dioxide injection was not used)
The preparation method of the preservative paper comprises the following steps:
adding tea polyphenol into water, heating to 55 ℃ under the condition of stirring, adjusting the pH of the obtained solution to about 1.5, maintaining the pH for reaction for 5 hours, and continuously adding the tea polyphenol during the reaction period; after reaction, rotary steaming, concentration and vacuum drying are carried out to obtain the tea polyphenol hydrolysate.
Adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 70 ℃, and carrying out vacuum reaction for 3 hours; adding a tea polyphenol hydrolysate with the mass of 0.3wt% of lactic acid, heating to 130 ℃, performing dehydration and polycondensation reaction for 4 hours, further heating to 200 ℃, continuing the reaction for 3 hours, draining, cooling, separating the product, and granulating to obtain the hybrid polylactic acid particles.
Mixing hybrid polylactic acid particles and nano cellulose according to a mass ratio of 98:2, adding the mixture into an injection molding machine, heating, pressurizing and melting, and introducing carbon dioxide into the injection molding machine to fully blend the mixture and a hybrid polylactic acid melt, wherein the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 300 mL/kg; the flow rate of carbon dioxide was 35mL/min, and an uncured polylactic acid foam was obtained after extrusion.
Taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper (0.2 mm), standing and curing at 45 ℃ for 30min to obtain the double-layer composite paper with the polylactic acid foam layer (0.2 mm).
And (3) soaking the double-layer composite paper in 0.4wt% ascorbic acid solution for 5s, taking out after soaking, and drying. The impregnation amount was 0.75 g/m2。
Dissolving sodium alginate in 16wt% oxidized starch solution (gelatinized at 95 ℃) to obtain coating liquid; the concentration of sodium alginate in the coating liquid was 1 wt%.
Uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper to form a coating layer, wherein the coating amount is controlled to be 10 g/m2And fully drying to obtain the preservative paper.
For the two-ply composite paper (base paper + polylactic acid foam layer) obtained in the production of example 1 and comparative example 4The gram weight is detected, and the result is as follows: the grammage of the two-ply composite paper in example 1 was 171g/m2The grammage of the two-ply composite paper of comparative example 4 was 182g/m2. The lower grammage of the two-ply composite paper of example 1 demonstrates that the polylactic acid foam layer of example 1 has a higher porosity and is lighter.
Effect testing
Kiwi fruit sold in the Lingan district of Hangzhou city, Zhejiang province is taken as a test material, and the influence of wrapping of preservative paper on the ripening process of the picked Kiwi fruit at normal temperature is discussed.
Firstly, fresh-keeping treatment is carried out on kiwi fruits, and the method specifically comprises the following steps:
the purchased kiwifruits sold on the market are randomly and evenly divided into 8 groups of 6 kiwifruits. Group 1 was blank and was not treated; group 2 was the experimental group (example 1), groups 3-6 were the control groups (comparative examples 1-4, respectively), and groups 7-8 were the artificially aged (50 ℃, 10 days) fresh-keeping papers of example 1 and comparative example 2, respectively. Wrapping the kiwi fruits by using preservative paper respectively; the 8 groups of kiwi fruits were stored at room temperature for 23 days. And simultaneously, the indexes of the hardness, the relative conductivity, titratable acid, soluble solid and the like of the kiwi fruits stored for 0h are measured.
Secondly, carrying out a series of measurements on the stored kiwi fruits: the assay covers the following aspects: hardness, relative conductivity, titratable acids, soluble solids.
And thirdly, evaluating the curing and fresh-keeping effects.
(1) Hardness index analysis
Fruits contain more protopectin, but as the fruits mature, the protopectin gradually degrades into water-soluble pectin, which causes cell wall degradation, hardness reduction and fruit softening. The hardness value can reflect the maturity degree of the picked kiwi fruits in the storage process and influence the edible mouthfeel of the kiwi fruits, so the hardness value is an important quality index.
In the storage process, 8 groups of kiwi fruits are gradually softened (as shown in figure 1), wherein the hardness of the kiwi fruits in groups 2-8 is lower than that of the kiwi fruits in a blank group, and the softening is more obvious, so that the aging of the kiwi fruits can be obviously promoted by wrapping the preservative paper, and the palatability of the kiwi fruits is improved. In addition, we observed that the softening phenomenon occurred for about 7 days in groups 2 to 4 and 6 to 8 before group 1, and the softening phenomenon occurred for about 5 days in group 5 before group 1, and analyzed the reason why the pores on the surface of the polylactic acid foam layer of the preservative paper of group 5 (example 3) were not closed, and part of ethylene was adsorbed, which affects the artificial ripening effect.
(2) Relative conductivity index analysis
The senescence of plant tissues is closely related to the degradation of biological membranes, and the primary characteristic of the early senescence stage of fruits is the loss of membrane integrity and function, wherein the peroxidation of membrane lipid is one of the important causes for fruit senescence.
After the storage is finished, the relative conductivity of 8 groups of kiwi fruits is increased (as shown in fig. 2), but the relative conductivity of the blank group (group 1) is obviously higher than that of the groups 2-8, and meanwhile, the rotting condition in the kiwi fruits can be obviously found by peeling off the skin, which shows that although the hardness of the blank group of kiwi fruits is well maintained, the blank group of kiwi fruits has the phenomenon that the softening stage is skipped and the kiwi fruits directly step into the rotting stage. The relative conductivity of the kiwi fruits of the groups 2-8 is increased compared with that before storage, but is lower than that of the blank group, which shows that during the storage period, the kiwi fruits of the group are frequently exchanged in the process of gradually maturing, and the nutrient substances are increased in the process, and meanwhile, the preservative paper of the groups 2 and 4-8 contains preservative materials, so that the good quality of the kiwi fruits during the storage period can be well maintained, the aging and the decay of the kiwi fruits are slowed down, and the kiwi fruits can be regarded as being normally softened. And because the preservative paper of the group 3 does not contain a preservative material, the preservative paper can only play a role in physical barrier preservation after wrapping the kiwi fruits, and the preservation effect is relatively poor. In addition, the conductivity of group 7 was lower than that of group 8, and the reason for this analysis was probably that the freshness-retaining paper of comparative example 2 (group 8) was partially precipitated after artificial aging, and therefore the freshness-retaining effect was affected.
(3) Solid acid ratio index analysis
The soluble solid is composed of sugar, pectin, organic acid, tannin and some mineral substances, vitamins, pigments and other components which can be dissolved in water, and the components directly influence the flavor of fruits and vegetables; titratable acid is also one of important indexes influencing the flavor, taste and nutritional value of fruits and vegetables, and the content of titratable acid is gradually degraded in the storage period; the solid acid ratio is an important index for evaluating the flavor and the maturity of fruits, and the larger the solid acid ratio is, the stronger the fruit flavor is, and the better the palatability is.
After 552h of storage, the solid acid ratio of 8 groups of kiwi fruits is remarkably increased (as shown in fig. 3), wherein the solid acid ratio of 2-6 groups of kiwi fruits is larger than that of 1 group, which shows that the kiwi fruits wrapped by preservative paper have better flavor after the storage is finished, and are more suitable for consumers to purchase and eat. Meanwhile, in groups 2-6, the preservative paper of group 3 does not contain preservative materials, so that partial decay occurs and the flavor is poor. In addition, group 7 had a poor flavor compared to group 8, and the reason for this analysis was probably that the preservative material of the preservative paper of comparative example 2 (group 8) was partially precipitated after artificial aging, and thus the preservation effect was affected.
Unless otherwise specified, the reagents designed in the examples of the present invention are all commercially available products, and all of them are commercially available.
The foregoing is directed to embodiments of the present invention, and not to all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (10)
1. The utility model provides a preservative paper for kiwi fruit postharvest curing which characterized in that: the preparation method comprises the following steps:
1) taking base paper, uniformly applying uncured polylactic acid foam material on one surface of the base paper, and curing to obtain double-layer composite paper with a polylactic acid foam layer;
2) dipping the double-layer composite paper in an ascorbic acid solution, taking out the dipped double-layer composite paper and drying the dipped double-layer composite paper;
3) dissolving sodium alginate in the oxidized starch solution to obtain a coating liquid;
4) and (3) uniformly coating the coating liquid on the surface of the polylactic acid foam layer of the paper obtained in the step 2) to form a coating layer, and fully drying to obtain the preservative paper.
2. The preservative paper according to claim 1, wherein in step 1), the thickness of the base paper is 0.175 to 0.2mm, and the thickness of the polylactic acid foam layer is 0.15 to 0.2 mm.
3. The preservative paper according to claim 1, wherein in the step 1), the aging condition is 40-50 ℃, and the paper is left standing for 20-40 min.
4. The preservative paper according to claim 1 or 3, wherein the uncured polylactic acid foam material is prepared by the following method in step 1):
A) adding tea polyphenols into water, heating to 50-60 deg.C under stirring, adjusting pH of the obtained solution to 1-2, maintaining pH for reaction for 4-6h, and continuously adding tea polyphenols during reaction period; after reaction, rotary steaming, concentrating and vacuum drying to obtain a tea polyphenol hydrolysate;
B) adding lactic acid into a vacuum reaction kettle using a water solvent, heating to 65-75 ℃, and carrying out vacuum reaction for 2-4 h; adding a tea polyphenol hydrolysate, heating to the temperature of 120-;
C) and mixing the hybrid polylactic acid particles and the nano cellulose according to the mass ratio of (97: 3) - (99: 1), adding the mixture into an injection molding machine, heating, pressurizing and melting, introducing carbon dioxide into the injection molding machine to fully blend the mixture with the hybrid polylactic acid melt, and extruding to obtain the uncured polylactic acid foam material.
5. The preservative paper according to claim 4, wherein: in the step B), the addition amount of the tea polyphenol hydrolysate is 0.1-0.5wt% of the lactic acid.
6. The preservative paper according to claim 4, wherein: in the step C), the volume mass ratio of the carbon dioxide to the hybrid polylactic acid particles is 100-500 mL/kg; wherein the introduction process of the carbon dioxide comprises the following steps: firstly, 70-80% of carbon dioxide is introduced at the rate of 30-40mL/min, and then the rest carbon dioxide is introduced at the rate of 10-20 mL/min.
7. The preservative paper according to claim 1, wherein in the step 2), the concentration of the ascorbic acid solution is 0.2 to 0.6wt%, the dipping time is 3 to 7s, and the dipping amount is 0.5 to 1.0 g/m2。
8. The preservative paper according to claim 1, wherein in the step 3), the concentration of the oxidized starch solution is 10-20 wt%; the concentration of sodium alginate in the coating liquid is 0.5-1.5 wt%.
9. The preservative paper according to claim 1, wherein in the step 4), the coating amount is controlled to 9.5 to 10.5 g/m2。
10. A method for curing picked kiwi fruits is characterized by comprising the following steps: wrapping the picked kiwi fruits with the preservative paper according to any one of claims 1 to 9, and then storing the kiwi fruits to promote ripening of the kiwi fruits.
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