CN110643078B - Low-moisture-permeability edible composite preservative film and preparation method thereof - Google Patents
Low-moisture-permeability edible composite preservative film and preparation method thereof Download PDFInfo
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- 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
- B65D65/463—Edible packaging materials
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- 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
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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
- C08J2305/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2301/00 or C08J2303/00
- C08J2305/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
- C08K3/20—Oxides; Hydroxides
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- C08K2003/2296—Oxides; Hydroxides of metals of zinc
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K2201/00—Specific properties of additives
- C08K2201/011—Nanostructured additives
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
- C08K5/05—Alcohols; Metal alcoholates
- C08K5/053—Polyhydroxylic alcohols
Abstract
The invention discloses an edible composite preservative film with low moisture permeability and a preparation method thereof. The preparation method of the preservative film comprises the following steps: adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 1-3%, controlling the concentrations of the chitosan, the nano zinc oxide and the glycerol in the system to be 0.02g/mL, 0.004g/mL and 0.004g/mL respectively, then heating to 50 ℃, keeping the temperature, stirring until the mixture is uniformly dispersed, and then ultrasonically degassing to obtain a composite membrane liquid; and casting the obtained composite membrane liquid into a membrane, and drying to obtain the composite membrane. The composite preservative film has a good preservation effect, is simple in preparation method, can be simply mixed, dispersed and cast into a film, and is low in production cost and energy consumption.
Description
Technical Field
The invention relates to a preservative film, in particular to an edible composite preservative film with low moisture permeability and a preparation method thereof.
Background
The main source of the existing food packaging material is petroleum-based polymer (represented by polyethylene or polypropylene), and the environmental pollution problem and the food safety problem caused by the material become more prominent with the increase of consumption. The birth of the edible fresh-keeping packaging material not only solves the problem of safe and rapid degradation of the food packaging material, but also can play a role in separation, thereby ensuring the safety of food.
Chitosan is a polysaccharide organic polymer obtained by deacetylation reaction of chitin. The chitosan molecules are highly entangled, and the highly deacetylated chitosan molecules have more crystal structures and stronger molecular rigidity, so that the chitosan has film forming property, and in addition, the chitosan also has the advantages of biocompatibility, biodegradability, no toxicity, no pollution and the like, so that the chitosan becomes an excellent material for preparing food packaging films. Nevertheless, the chitosan alone as the film forming material still has the disadvantages of poor mechanical properties, poor water resistance, etc. of the obtained film. The current research is mainly to improve the performance of the chitosan food packaging film by improving the formula of the chitosan packaging film. For example, the invention patent with the publication number of CN109776834A discloses a preparation method of preservative and bacteriostatic preservative film, which comprises the following steps: (1) weighing 80-112 parts of polypropylene, 5-7 parts of copper powder, 20-28 parts of zinc oxide, 1-3 parts of graphene, 5-8 parts of acetic acid, 3-5 parts of glycerol and 5-10 parts of chitosan as raw materials in parts by weight; (2) uniformly mixing the raw materials, performing melt extrusion in an extruder, and performing blow molding to obtain a base film; (3) and respectively spraying a layer of protective film on the upper surface and the lower surface of the base film to obtain the preservative film. The formula of the protective film is as follows: 80-100 parts of water, 10-20 parts of ginger extract, 8-16 parts of edible alcohol, 3-8 parts of ferrous sulfate, 10-15 parts of citric acid, 6-18 parts of hydroxymethyl cellulose and 1-8 parts of sodium tripolyphosphate. The invention indicates that the added copper oxide and zinc oxide can decompose ethylene into water and carbon dioxide, and the ethylene is a strong cause for quick ripening and rotting of fruits and vegetables, so the invention can prolong the fresh-keeping time of the fruits and the vegetables. However, the base film still contains petroleum-based polymer, the formula is complex, and all components need to be melted and then extruded and blown to obtain the base film, so that the requirement on production equipment (an extruder is needed) is high, the cost is high, and the energy consumption (melting) is high.
Disclosure of Invention
The invention aims to solve the technical problem of providing the low-moisture-permeability edible composite preservative film with simple formula and good preservation effect and the preparation method thereof.
The invention relates to a preparation method of a low-moisture-permeability edible composite preservative film, which comprises the following steps: adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 1-3%, controlling the concentrations of the chitosan, the nano zinc oxide and the glycerol in the system to be 0.02g/mL, 0.004g/mL and 0.004g/mL respectively, then heating to 50 ℃, keeping the temperature, stirring until the mixture is uniformly dispersed, and then ultrasonically degassing to obtain a composite membrane liquid; and (3) casting the obtained composite membrane liquid into a membrane, and drying to obtain the low-moisture-permeability edible composite preservative membrane.
In the above preparation method, the time for stirring under heat preservation is preferably 20min, and the time for ultrasonic degassing is preferably 20-40min, and more preferably 30 min.
In the above preparation method, chitosan, nano zinc oxide and glycerol are preferably added to a glacial acetic acid solution with a volume concentration of 2%.
The invention also comprises the edible composite preservative film with low moisture permeability prepared by the method.
The invention is characterized in that:
1. based on 1-3% of glacial acetic acid solution, chitosan, nano zinc oxide and glycerol are added into the glacial acetic acid solution, the specific concentrations of the chitosan, the nano zinc oxide and the glycerol are limited, and the glacial acetic acid solution is stirred at a specific temperature in a heat preservation mode until the components are uniformly dispersed, so that the preservative film obtained by casting the obtained composite film liquid has a lower water vapor transmission coefficient, and a better preservative effect is achieved (compared with a chitosan film, the nutrition loss in fruits after 10 days of preservation is less).
2. The preservative film is non-toxic, pollution-free and degradable; the preparation method is simple, only needs simple mixing and even dispersion, and then carries out tape casting to form the film, and has low production cost and low energy consumption.
Drawings
FIG. 1 is a graph showing the influence of the addition of chitosan on the water vapor transmission rate of a chitosan composite membrane;
FIG. 2 is a graph showing the influence of the addition of nano ZnO on the water vapor transmission coefficient of the chitosan composite film;
FIG. 3 is a graph showing the influence of the addition of glycerol on the water vapor transmission coefficient of a chitosan composite membrane;
FIG. 4 is a graph showing the influence of different stirring temperatures on the water vapor transmission coefficient of the chitosan composite membrane;
FIG. 5 is a graph showing the influence of different stirring times on the water vapor transmission coefficient of the chitosan composite membrane;
FIG. 6 is a picture of the loquat in the treatment group A after being stored for 10 days at normal temperature;
FIG. 7 is a photograph of the loquat in the treatment group B after being stored for 10 days at normal temperature;
FIG. 8 is a photograph of the loquat in the treatment group C after being stored at room temperature for 10 days;
FIG. 9 is a photograph of the loquat in the treatment group D after being stored at room temperature for 10 days;
FIG. 10 is a graph showing the change of the fruit-improving rate of the loquat during storage in different treatment groups;
FIG. 11 is a graph showing the change of the weight loss ratio of the loquat during storage in different treatment groups;
FIG. 12 is a graph showing the variation of Vc content during the storage period of loquat in different treatment groups;
FIG. 13 is a graph showing the variation of soluble solids content during storage of Eriobotrya japonica according to the different treatment groups;
FIG. 14 is a graph showing the change of total acid content in loquat storage time in different treatment groups.
Detailed Description
The applicant determined the parameters of the method of the invention by the following orthogonal experiments.
1 Experimental materials and instruments
1.1 Main materials and reagents
TABLE 1 Main materials and reagents
1.2 Main instruments
TABLE 2 Main instruments
2 method of experiment
2.1 preparation of Chitosan Membrane
Dissolving chitosan in 2% glacial acetic acid solution, stirring at 50 deg.C for 20min, and ultrasonic degassing for 30min to obtain chitosan solution. Quantitatively casting the chitosan solution on a flat plate to form a film, drying and uncovering the film for later use.
2.2 preparation of Chitosan-Nano ZnO composite film
Dissolving a certain amount of nano zinc oxide (nano ZnO) in glycerol, adding 100mL of 2% glacial acetic acid solution, adding 2g of chitosan, stirring at 50 ℃ for 20min, and ultrasonically degassing for 30min to obtain the chitosan-nano ZnO composite membrane liquid. Quantitatively casting the chitosan-nano ZnO composite membrane liquid on a flat plate to form a membrane, drying and uncovering the membrane for later use.
2.3 determination of the Properties of the composite film
And placing the prepared composite membrane in a transparent glass dryer at room temperature for standing for later use.
2.3.1 measurement of film thickness
Selecting a flat and defect-free thin film, randomly measuring five points, and taking the average value as the thickness of the film.
2.3.2 measurement of Membrane Water vapor Transmission coefficient (WVP)
The water vapor permeability of the composite film was measured by a pseudo-cup method. At room temperature, anhydrous CaCl2The mixture is added into a weighing bottle with the diameter of 30X 50mm until the position of the bottle mouth is 5 mm. The smooth and flat part of the composite film is cut, the thickness of the composite film is measured, the composite film is placed into a bottle and fixed by a rubber ring, and then the composite film is weighed quickly. And (3) placing the weighed weighing bottle into a climatic chamber, and keeping the temperature at 25 ℃, namely under the condition that the relative humidity is 90%, ensuring that the water vapor pressure difference inside and outside the membrane is unchanged. And (4) taking out the weighing bottle at intervals and weighing until the difference between the mass increment of the two times is less than 5%, weighing for three times, calculating the average value, and calculating the water vapor transmission coefficient of the composite membrane by using the result expressed by delta m. The calculation formula is as follows:
wherein, WVP: water vapor transmission coefficient [ g.mm/(m)2·h·kPa)]；
d: thickness (mm) of the composite film;
Δ m: mass increase after stabilization (g);
a: area of the cut film (m)2)；
Δ t: measuring time interval (h), wherein the measuring interval in the experiment is 3 h;
Δ p: the fixed water vapor pressure difference (kPa) of the two sides of the composite membrane is 3.168kPa, because the relative humidity is kept 90 percent under the experiment at 25 ℃.
2.4 Single factor test
And (3) placing the composite membrane prepared in the step (2.2) in a climatic chamber, setting the temperature to be 25 ℃ and the relative humidity to be 90%, and measuring the influence of different factor conditions on the water vapor transmission coefficient of the composite membrane.
(1) Under the conditions that the addition amount of nano ZnO is 0.002g/mL and the addition amount of glycerin is 0.004g/mL, the addition amounts of chitosan are respectively 0.005, 0.01, 0.015, 0.02, 0.025 and 0.03g/mL, the stirring temperature is 30 ℃, the stirring time is 30min, and ultrasonic degassing is performed for 30min, the influence of chitosan on the water vapor transmission coefficient of the chitosan-nano ZnO composite membrane is considered, and the optimal addition amount of chitosan is determined.
(2) Under the conditions that the addition amount of chitosan is 0.02g/mL and the addition amount of glycerol is 0.004g/mL, the addition amounts of nano ZnO are respectively 0, 0.002, 0.004, 0.006, 0.008 and 0.01g/mL, the stirring temperature is 30 ℃, the stirring time is 30min, and ultrasonic degassing is performed for 30min, the influence of nano ZnO on the water vapor transmission coefficient of the chitosan-nano ZnO composite membrane is examined, and the optimal addition amount of nano ZnO is determined.
(3) Under the conditions that the addition amount of chitosan is 0.02g/mL and the addition amount of nano ZnO is 0.004g/mL, the addition amounts of glycerol are 0.002, 0.004, 0.006, 0.008 and 0.01g/mL respectively, the stirring temperature is 30 ℃, the stirring time is 30min, and ultrasonic degassing is performed for 30min, the influence of glycerol on the water vapor transmission coefficient of the chitosan-nano ZnO composite membrane is examined, and the optimal addition amount of glycerol is determined.
(4) Under the conditions that the addition amount of chitosan is 0.02g/mL, the addition amount of nano ZnO is 0.004g/mL and the addition amount of glycerol is 0.006g/mL, the stirring temperature is respectively 30 ℃, 40 ℃, 50 ℃, 60 ℃ and 70 ℃, the stirring time is 30min, and when ultrasonic degassing is carried out for 30min, the influence of the stirring temperature on the water vapor transmission coefficient of the chitosan-nano ZnO composite membrane is considered, and the optimal reaction temperature is determined.
(5) Under the conditions that the addition amount of chitosan is 0.02g/mL, the addition amount of nano ZnO is 0.004g/mL, the addition amount of glycerol is 0.006g/mL and the stirring temperature is 50 ℃, the stirring time is respectively 20min, 30min, 40min, 50min and 60min, and ultrasonic degassing is carried out for 30min, the influence of the stirring time on the water vapor transmission coefficient of the chitosan-nano ZnO composite membrane is examined, and the optimal stirring time is determined.
2.5 orthogonal test
Based on the results of the single-factor test, the water vapor transmission coefficient was used as an evaluation index, and the amounts of chitosan concentration, nano-ZnO concentration, and glycerin concentration were selected and subjected to L9 (3)3) Orthogonal test (table 3).
TABLE 3 orthogonal test factors and horizon
3 results and discussion
3.1 Effect of different Chitosan additions on the Water vapor Transmission coefficient of composite membranes
As can be seen from fig. 1, the water vapor permeability of the composite membrane tends to decrease and then increase as the amount of chitosan added increases. The water vapor transmission coefficient of the membrane is continuously decreased at 0.005 to 0.02g/mL, which is probably because the thinner the chitosan concentration is, the larger the water vapor transmission coefficient is, and the water vapor transmission rate of the membrane is increased at 0.02 to 0.03g/mL, which is probably because the chitosan membrane has water absorbency, and the higher the concentration is, the stronger the water absorbency is. When the chitosan addition amount is 0.02g/mL, the water vapor transmission coefficient of the composite membrane is the lowest, and the chitosan addition amount is selected to be 0.02g/mL in consideration of the film forming property of the composite membrane.
3.2 Effect of different Nano ZnO addition amounts on vapor transmission coefficient of composite film
As can be seen from fig. 2, the water vapor transmission coefficient of the composite film tends to decrease with the increase in the amount of nano ZnO, which is probably due to the effect of water blocking by adding nano ZnO. When the addition amount of the nano ZnO is 0.01g/mL, the steam transmission coefficient of the composite membrane is the lowest. When the addition amount of nano ZnO reaches 0.008g/mL, the composite film shows easy brittleness, so 0.004g/mL of nano ZnO is selected.
3.3 Effect of different Glycerol additions on the Water vapor Transmission coefficient of the composite Membrane
As can be seen from fig. 3, the water vapor permeability of the composite membrane tends to increase as the amount of glycerin added increases, which is probably because glycerin has water absorption. The water vapor transmission coefficients of the composite films with the glycerol addition amounts of 0.004g/mL, 0.006g/mL and 0.008g/mL are not greatly different, so the glycerol addition amount is selected to be 0.006 g/mL.
3.4 Effect of different stirring temperatures on the Water vapor Transmission coefficient of the composite Membrane
As can be seen from fig. 4, the water vapor permeability coefficient of the composite membrane is not large as the stirring temperature increases), which is probably because the stirring temperature has little influence on the composite membrane, and according to experimental observation, the higher the temperature is, the faster the composite membrane solution is dissolved. When the stirring temperature is 50 ℃, the water vapor permeability coefficient of the film is the lowest, so 50 ℃ is selected.
3.5 Effect of different stirring times on the Water vapor Transmission coefficient of the composite Membrane
As can be seen from fig. 5, the water vapor permeability of the composite membrane tends to gradually increase with the increase in the stirring time. According to experimental observation, when the stirring time is 20min, the composite membrane liquid is completely dissolved. This is probably because the stirring time was selected to be 20min because it does not greatly affect the water vapor permeability coefficient of the composite membrane.
3.6 analysis of orthogonal Experimental results
TABLE 4 results of orthogonal test factors and visual analysis table
As shown in Table 4, the optimum mixing ratio of the chitosan composite film is A2B2C1Namely, the concentration of chitosan is 0.02g/mL, the concentration of nano ZnO is 0.004g/mL, and the concentration of glycerol is 0.004 g/mL. From the range analysis, the main factor and the secondary factor which influence the water vapor transmission rate of the composite membrane are A>B>C, i.e. chitosan concentration>Concentration of nano ZnO>The concentration of glycerol.
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The chitosan is dissolved in slightly acidic water and is insoluble in water, and a solution formed after the chitosan is fully dissolved has certain viscosity, is natural high-molecular polysaccharide, is suitable for fruit and vegetable fresh-keeping, and is a fresh-keeping film required by the experiment. The chitosan polysaccharide film is yellowish and transparent in appearance, poor in toughness and easy to break. The composite membrane with the same concentration is easier to take off the flat plate than the chitosan membrane.
(1) The 0.02g/mL chitosan solution has certain film forming property and can form a layer of polysaccharide film.
(2) The optimal proportioning conditions of the composite membrane by taking the water vapor permeability as an index are that the chitosan concentration is 0.02g/mL, the nano ZnO concentration is 0.004g/mL, the glycerin concentration is 0.004g/mL, the stirring temperature is 50 ℃, and the stirring time is 20 min.
(3) According to experimental observation, the glycerol has the functions of dispersing nano ZnO and plasticizing in the composite film.
Example 1
Adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 2%, wherein the adding amounts of the chitosan, the nano zinc oxide and the glycerol are respectively 0.02g/mL, 0.004g/mL and 0.004g/mL in a control system, then heating to 50 ℃, stirring for 20min under heat preservation, and then ultrasonically degassing for 30min to obtain a composite membrane liquid; and (3) casting the obtained composite membrane liquid on a flat plate to form a membrane, drying at 80 ℃, and uncovering the membrane to obtain the edible composite preservative membrane with low moisture permeability.
Comparative example 1
Adding chitosan into glacial acetic acid solution with volume concentration of 2%, wherein the addition amount of the chitosan is 0.02g/mL, heating to 50 ℃, stirring for 20min, and ultrasonically degassing for 30min to obtain composite membrane liquid; and (3) casting the obtained composite membrane liquid on a flat plate to form a membrane, drying at the temperature of 80 ℃, and uncovering the membrane to obtain the chitosan membrane.
Example 2
Example 1 was repeated except that: adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 1%, ultrasonically degassing for 40min, forming a film on a flat plate, drying at 60 ℃, and uncovering the film to obtain the edible composite preservative film with low moisture permeability.
Example 3
Example 1 was repeated except that: adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 3%, ultrasonically degassing for 20min, forming a film on a flat plate, drying at 50 ℃, and uncovering the film to obtain the edible composite preservative film with low moisture permeability.
Experimental example: experiment on preservation effect of composite film
1 Experimental materials and instruments
1.1 Main materials and reagents
TABLE 5 Main materials and reagents
1.2 Main instruments
TABLE 6 Main Instrument
2 method of experiment
2.1 pretreatment of the fruit
Selecting fresh loquat fruits with the same maturity, no damage to the skin and uniform size, cutting and reserving a stem of about 1cm, washing with clear water and drying in the air. Loquat fruits were randomly grouped, and the experiment was set up with four treatment groups: group a (blank control), no treatment; group B (preservative film group, the preservative film is a PE preservative film purchased in the market), and fruits are wrapped by the preservative film; c group (chitosan film group, the chitosan film is the chitosan film prepared according to the method of the invention comparative example 1), and the fruit is wrapped by the chitosan film; and group D (composite film group, the composite film is the composite preservative film prepared by the method of the invention in the embodiment 1), and the fruit is wrapped by the composite film. Each treatment group will be stored at room temperature and the index change of the fruit measured every 2 days.
2.2 Change of Each index during storage
2.2.1 determination of good fruit percentage
In view of the taste and health requirements of the consumer, the test was conducted to determine the appearance of brown speckles in the size of the soybean grains, the color shift from yellow to brown in the peel and the appearance of slight off-flavors as the criteria for the non-integrity of the fruit. □ □
2.2.2 measurement of weight loss ratio
2.2.3 determination of vitamin C content
With reference to GB5009.86-2016, the determination was carried out by 2, 6-dichloroindophenol titration.
2.2.4 measurement of soluble solid content%
The measurements were performed using a hand-held glucometer.
2.2.5 determination of titratable acid content
Measured by acid-base titration indicator method[11]。
3 results and analysis
3.1 loquat fresh-keeping picture
3.1.1 fresh loquat
The fresh loquat is picked the same day and transported back to the laboratory, after pretreatment and air drying, the loquat is stored at room temperature, and the loquat stored the first day is plump and bright yellow in color.
3.1.2 loquat leaves after 10 days storage
A. B, C and the loquats of the D-treated group after 10 days of storage at ambient temperature are shown in FIGS. 6-9, respectively.
As can be seen in FIGS. 6-9, the loquat in group A is mostly rotten and deteriorated; the appearance of group B was mostly intact; partial fruit shriveling in group C; the loquat fruits in group D are still plump and brown, and can be eaten.
Storing the loquat which is not treated for 10 days at room temperature, namely 80% of fruits are rotten; the composite film of the invention is adopted to carry out room temperature fresh keeping on the loquat, and shows good fresh keeping effect.
3.2 Effect of different treatments on the good fruit Rate of loquat
As can be seen from FIG. 10, the good fruit rate of the loquat fruits gradually decreased as the storage time increased. The good fruit rate of the group A is reduced rapidly, the good fruit rate is only 20% after 10 days of storage, and the reduction rate is obviously faster than that of the B, C, D groups. The good fruit rate of the B group is the best, and the D group is the next, but the composite film has the advantages of no toxicity, edible property, biodegradability and the like compared with the preservative film.
3.3 Effect of different treatments on loquat weight loss ratio
As can be seen from fig. 11, the weight loss rates of the loquats treated in different ways during the over-storage period all showed an upward trend. This is due to the loss of water inside the fruit which results in a loss of quality. Group a trended the fastest, with group B being 8.16% lower than group a on day 10 of storage. The weight loss ratios of the group C and the group D are respectively 2.79 percent and 3.63 percent lower than that of the control group, probably because the nano zinc oxide is added into the composite membrane, the moisture permeability of the composite membrane is improved to a certain extent, and the weight loss ratio of the group D is lower than that of the group C.
3.4 Effect of different treatments on the vitamin C content of Eriobotrya japonica
Vitamin C is an important nutrient substance in fruits and vegetables, and has the effects of resisting oxidation and slowing down aging. As can be seen from fig. 12, the vitamin C content of the loquats treated differently showed a decreasing trend with increasing storage time, wherein the decrease rate of the vitamin C content of the fruits treated in group D was slower than that of the fruits treated in groups a, B and C, indicating that the composite film inhibited the decrease of the vitamin C content of the fruits to some extent, and thus, effectively slowed the loss of the nutritional components of the loquats.
3.5 Effect of different treatments on soluble solids content of Eriobotrya japonica
As can be seen from FIG. 13, the soluble solids content of loquat fruits treated differently at room temperature decreased during storage, indicating that the sugar content of loquat was decreased due to respiration. On the whole, the decrease speed of the soluble solid content of the group D is slower and is obviously lower than that of the group A, probably because the composite membrane can delay the decrease of the soluble solid content in the loquat fruits to a certain extent, thereby achieving the effects of delaying the senescence of the fruits and improving the storability of the loquats.
3.6 Effect of different treatments on titratable acid content in Eriobotrya japonica
Titratable acid content is an important chemical index for fruit quality identification. As can be seen from FIG. 14, the titratable acid content of the loquats in different treatments decreased during storage, wherein the group A decreased most rapidly due to the respiration consumption of the fruits. The D group is reduced slower than the A group, which probably means that the composite film of the invention slows the respiratory metabolism of the fruit to a certain extent and effectively delays the reduction of the titratable acid content during the storage period of the fruit.
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The composite film disclosed by the invention has a good preservation effect on the loquats, and can effectively delay the shelf life of the loquats.
(1) Days for preservation, 10 days.
(2) The composite film has good fresh-keeping effect on the loquat, maintains good fruit rate in the storage period, and slows down the reduction of the vitamin C content, the soluble solid content and the titratable acid content of the fruits. The composite film is wrapped on the surface of the fruit, so that the infection of exogenous microorganisms can be reduced, and a good fresh-keeping effect is achieved.
Claims (5)
1. A preparation method of a low-moisture-permeability edible composite preservative film is characterized by comprising the following steps: adding chitosan, nano zinc oxide and glycerol into a glacial acetic acid solution with the volume concentration of 1-3%, controlling the concentrations of the chitosan, the nano zinc oxide and the glycerol in the system to be 0.02g/mL, 0.004g/mL and 0.004g/mL respectively, then heating to 50 ℃, keeping the temperature, stirring until the mixture is uniformly dispersed, and then ultrasonically degassing to obtain a composite membrane liquid; and (3) casting the obtained composite membrane liquid into a membrane, and drying to obtain the low-moisture-permeability edible composite preservative membrane.
2. The preparation method of the low moisture permeability edible composite preservative film according to claim 1, characterized in that: the stirring time is 20 min.
3. The preparation method of the low moisture permeability edible composite preservative film according to claim 1, characterized in that: ultrasonic degassing time is 20-40 min.
4. The preparation method of the low moisture permeability edible composite preservative film according to any one of claims 1 to 3, characterized in that: adding chitosan, nano zinc oxide and glycerol into glacial acetic acid solution with the volume concentration of 2%.
5. The low-moisture-permeability edible composite preservative film prepared by the method of any one of claims 1 to 4.
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| CN201910828502.6A CN110643078B (en) | 2019-09-03 | 2019-09-03 | Low-moisture-permeability edible composite preservative film and preparation method thereof |
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