阅读说明：本技术 一种低透湿性可食性复合保鲜膜及其制备方法 (Low-moisture-permeability edible composite preservative film and preparation method thereof ) 是由 韦巧艳 廖政达 覃逸明 谢济运 李乃干 蓝峻峰 李大成 周永升 陈碧 柳富杰 邓 于 2019-09-03 设计创作，主要内容包括：本发明公开了一种低透湿性可食性复合保鲜膜及其制备方法。该保鲜膜的制备方法为：在体积浓度为1-3％的冰醋酸溶液中加入壳聚糖、纳米氧化锌和甘油,控制体系中壳聚糖、纳米氧化锌和甘油的浓度分别为0.02g/mL、0.004g/mL和0.004g/mL,然后升温至50℃,保温搅拌至分散均匀,之后超声脱气,得到复合膜液；所得复合膜液流延成膜,干燥,即得。本发明所述复合保鲜膜具有较好的保鲜效果,且制备方法简单,仅需简单混合分散均匀后流延成膜即可,生产成本低,能耗也低。(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.)

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 5.

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.

4 small knot

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.