Ethylene adsorption type laser drilling freshness protection bag

Abstract

The invention discloses an ethylene adsorption type laser drilling freshness protection bag, and relates to a double-layer passive air-conditioning freshness protection bag adopting a laser drilling technology, an ethylene adsorption technology and an anti-fog technology. The invention belongs to the technical field of fruit and vegetable preservation. The composite material is composed of a structural layer made of an inner layer and an outer layer, wherein the inner layer is mainly made of EVA (ethylene-vinyl acetate copolymer) and ethylene adsorption powder; the main materials of the outer layer are LDPE (Low Density Polyethylene) and EVA (Ethylene Vinyl Acetate), the micropores can further improve the oxygen permeability, carbon dioxide permeability and moisture permeability of the film, and the thickness ratio of the inner layer to the outer layer of the film and the total thickness of the film are adjustable. The special preservation bag for winter jujubes prepared by the process can adsorb ethylene and prevent fog, passively establishes an environment with high oxygen concentration, low carbon dioxide concentration and relative humidity (RH) of 90-95%, and is especially suitable for preservation of winter jujubes.

Description

Technical Field

[0001] The present invention relates to a design and preparation method of a double-layer passive atmosphere-controlled fresh-keeping bag combining laser drilling technology, ethylene adsorption technology and anti-fogging technology, which is particularly suitable for preserving carbon dioxide-intolerant fruit and vegetable agricultural products such as winter jujube, and belongs to the field of fruit and vegetable preservation technology. Background Art

[0002] Winter jujube is also known as Yanlaihong, frozen jujube, and apple jujube. It is rich in nutrients and can be eaten fresh or processed into candied jujube, drunken jujube, jujube cake, canned jujube, etc. It can also be made into jujube tea, jujube juice, jujube paste and other products. Winter jujube is rich in carbohydrates, proteins, vitamins A, C, E, and various trace elements such as potassium, sodium, iron, and copper. The content of vitamin C is extremely high, which is 70 times that of apples and 16 times that of citrus. It is the most nutritious fruit and is known as the "living vitamin pill". It has the effects of beautifying and nourishing the skin, strengthening the spleen and stomach, nourishing the liver, preventing and treating cardiovascular diseases, regulating immunity, and sobering up. Winter jujube has a high metabolic activity and is prone to water loss during storage, resulting in reduced freshness. Fresh jujube is prone to accumulate ethanol in the pulp to maintain its own respiration, which accelerates the softening of the pulp. In addition, fresh jujube is particularly sensitive to carbon dioxide content, so fresh jujube becomes a fruit that is very difficult to preserve.

[0003] At present, the commonly used preservation methods include quick freezing storage, gas conditioning storage, reduced pressure storage, ozone preservation storage, magnetic field sterilization preservation, preservative preservation, biotechnology preservation, and fresh-keeping bag preservation. Quick freezing storage, gas conditioning storage, reduced pressure storage, ozone preservation storage, magnetic field sterilization preservation generally have the problem of high cost, and preservative preservation has the problem of toxic substances remaining and endangering human health. The existing biotechnology preservation technology is not mature, so the most commonly used preservation method on the market is fresh-keeping bag preservation, but the existing fresh-keeping packaging has the problem of low water permeability and insufficient carbon dioxide permeability, so that the existing fresh-keeping bag packaging has unsatisfactory preservation ability. Summary of the invention

[0004] To solve the above problems, the present invention proposes a special fresh-keeping bag for winter jujube. The fresh-keeping bag adopts a double-layer film structure and combines laser drilling, ethylene adsorption, anti-fog, and passive gas conditioning technology to prevent fogging and adsorption of ethylene, and passively adjusts the concentration of oxygen and carbon dioxide in the fresh-keeping bag and the relative humidity, so that the atmosphere in the bag becomes an atmosphere suitable for winter jujube preservation and dormancy, that is, reducing the carbon dioxide content to prevent the damage caused by the high carbon dioxide concentration in the fresh-keeping bag to the winter jujube. Winter jujube is particularly sensitive to carbon dioxide. Under higher carbon dioxide concentrations, the winter jujube pulp will undergo saccharification, the hardness will decrease, and the pulp will rot. Slightly reducing the oxygen content reduces the respiration rate of the winter jujube but will not breathe anaerobicly, reduces the water vapor content (relative humidity RH) in the bag, prevents the water vapor in the bag from being supersaturated to cause water droplets to condense and breed mold, and adsorbs the ethylene released by the winter jujube breathing to prevent the winter jujube from self-ripening. Finally, the anti-fog inner layer in the bag can further prevent the generation of water mist and prevent bacterial growth. The purpose of extending the fresh-keeping time of the winter jujube is finally achieved.

[0005] The utility model discloses an ethylene adsorption type laser perforated fresh-keeping bag, which consists of an inner and outer two-layer structure. The inner layer is a blend of EVA (ethylene-vinyl acetate copolymer) and ethylene adsorption powder, and the outer layer is a blend of LDPE (low-density polyethylene) and EVA. The two layers of film are blown out at one time by an AB type film blowing machine, then punched by a laser punching machine, and finally made into a bag.

[0006] The ethylene adsorption powder is aluminum silicate crystals; the specific preparation method of aluminum silicate crystals comprises the following steps: (1) dissolving 100 parts (by weight, the same below) of sodium silicate and 6 parts of anhydrous aluminum nitrate in distilled water respectively, and then mixing the two solutions under stirring and adjusting the pH value to 6 to 6.5 with nitric acid so that they are complexed in water to form an aluminosilicate gel; (2) evaporating excess water in the aluminosilicate gel by spray drying; (3) calcining at a high temperature of 500°C-600°C to evaporate the crystal water in the aluminosilicate gel, gasify and decompose the nitrate byproduct, and generate aluminum silicate crystals, i.e., the corresponding ethylene adsorption powder; wherein the aluminum silicate crystals The principle of ethylene adsorption is: the raw material sodium silicate solution provides silicon ions, and the aluminum nitrate solution provides aluminum ions. Since silicon and aluminum ions have 4 and 3 active sites respectively, there are active site vacancies when generating aluminosilicate gel. These hole active sites form adsorption active sites after drying and burning, which can adsorb substances with rich electron structures such as ethylene. The tetravalent silicon ions and trivalent aluminum ions in the burned aluminosilicate compounds produce lattice defects (holes) when stacking to form a lattice. These holes have the ability to adsorb substances with rich electron structures, and the metabolic product ethylene of winter jujube has a high electron cloud density. After being captured by the holes, it cannot continue to ripen agricultural products such as winter jujube.

[0007] The raw material of the inner layer is made by melt co-extrusion and pelletizing of 100 parts of EVA resin and 40-60 parts of ethylene adsorption powder, preferably melted at 145-150°C; the ethylene adsorption powder can adsorb ethylene and has an anti-fog effect due to its strong polarity.

[0008] The raw material of the outer layer is made by adding 40-60 parts of EVA resin to 100 parts of LDPE resin, melt co-extrusion and pelletizing, preferably melted at 145-150°C. The main advantage of LDPE resin is that it is easy to be processed by blown film. And because the main component of the inner film is EVA, and a large proportion of EVA is also added to the outer film, the compatibility of the inner film and the outer film is very good, and the processing temperature of LDPE can be reduced from 190°C to 150°C. And because EVA has the physical property of high water vapor, oxygen and carbon dioxide permeability, its addition to the film can passively adjust the atmosphere in the bag, making the atmosphere suitable for the preservation and dormancy of winter jujube.

[0009] After the raw resins of the inner and outer layers are prepared, the total film thickness is controlled between 30 and 50 microns at 150°C using an AB-type film blowing machine, and the thickness ratio of the inner and outer layers is 40%:60% to 60%:40%. The outer layer mainly provides the bag with processing performance and water retention performance, while the inner layer mainly provides the bag with air permeability, water permeability, ethylene adsorption and anti-fog performance.

[0010] Then, after the double-layer composite film is blown into shape, a laser puncher is used to punch holes with a diameter of 30-50 microns every 0.5-1.5 cm on the film; finally, a bag making machine is used to make bags. Punching holes will greatly increase the permeability of carbon dioxide, because a high carbon dioxide environment is very unfavorable to winter dates. DETAILED DESCRIPTION

[0011] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0012] Embodiment 1:

[0013] Preparation of ethylene adsorption powder: Pour 100 parts of water glass into 80 parts of deionized water and stir until a water glass solution is formed. Pour 6 parts of anhydrous aluminum nitrate into 80 parts of deionized water and stir until an aluminum nitrate solution is formed. Add the water glass solution into a stainless steel reactor, and then gradually add the aluminum nitrate solution to the water glass solution at 60 degrees Celsius and under stirring, and complete the addition within 30 minutes. Stir at high speed for one hour at a speed of 600 rpm. Then gradually add the dilute sulfuric acid solution to the above-prepared solution and stir until the pH value reaches 6 to 6.5, and the aluminosilicate gel is prepared. Then transfer the prepared aluminosilicate gel to a spray drying device and spray dry until the excess water in the aluminosilicate gel is evaporated to obtain a powder containing crystal water. Finally, add the powder into a muffle furnace and calcine at 500°C to 600°C for 4 to 5 hours to remove the crystal water in the powder and obtain a crystalline powder containing active sites (holes).

[0014] Preparation of raw resin for inner layer film: put 100 parts of EVA resin and 40 parts of ethylene adsorption powder into a high-speed mixer, stir for 5 minutes at a speed of 500 rpm, add the mixture into the hopper of a twin-screw extruder, set the temperature of the heating section of the extruder to 80-145-145-150-150°C, melt blend at a screw speed of 100 rpm to obtain modified EVA resin strips, and cut them into modified EVA resin particles with a length of 2-3 mm on a pelletizer.

[0015] Preparation of raw material resin for outer layer film: put 100 parts of LDPE resin and 40 parts of EVA resin into a high-speed mixer, stir for 5 minutes at a speed of 500 rpm, add the mixture into the hopper of a twin-screw extruder, set the temperature of the heating section of the extruder to 80-145-145-150-150°C, melt blend at a speed of 100 rpm to obtain modified LDPE resin strips, and cut them into modified LDPE resin particles with a length of 2-3 mm on a pelletizer.

[0016] Preparation of double-layer composite film: Set the heating section temperature, connector and die head of the two screws of the AB type film blowing machine equipped with two single-screw conveying devices to 100-145-145-150-150-150°C respectively, place the inner layer film raw material resin particles in the corresponding inner layer single screw conveying hopper, place the outer layer film raw material resin particles in the corresponding outer layer single screw conveying hopper, adjust the inner layer screw speed to 25rpm, adjust the outer layer screw speed to 30rpm, adjust the blowing ratio of the film bubble to 2, and the traction ratio to 4, to obtain a double-layer composite film with a thickness of 50 microns, of which the inner layer thickness is 20 microns and the outer layer thickness is 30 microns.

[0017] The double-layer composite film was processed using a laser puncher: a 30-micron hole was punched every 1.5 cm on the composite film using a laser puncher.

[0018] Bag making: The film processed by laser punching machine is sealed on three sides to make a fresh-keeping bag with an outer size of 30×25 cm, namely the winter jujube fresh-keeping bag. 500 grams of winter jujube and a small electronic hygrometer are added to the bag, which is sealed and stored in an environment of 25-30℃ for 5 days. Then, the quality of the winter jujube is tested.

[0019] Embodiment 2:

[0020] Preparation of ethylene adsorption powder: Ethylene adsorption powder was prepared under the same conditions as in Example 1.

[0021] Preparation of raw material resin for inner layer film: 100 parts of EVA resin and 50 parts of ethylene adsorption powder were put into a high-speed mixer, and other conditions were the same as those in Example 1 to prepare raw material resin for inner layer film.

[0022] Preparation of raw material resin for outer layer film: 100 parts of LDPE resin and 50 parts of EVA resin were put into a high-speed mixer, and other conditions were the same as those in Example 1 to prepare raw material resin for outer layer film.

[0023] Preparation of double-layer composite film: The inner layer screw speed described in Example 1 is adjusted to 26.5rpm, the outer layer screw speed is adjusted to 26.5rpm, and the other conditions are the same as Example 1, to prepare a double-layer composite film with a thickness of 40 microns, of which the inner layer thickness is 20 microns and the outer layer thickness is 20 microns.

[0024] The double-layer composite film is processed using a laser puncher: the conditions are the same as in Example 1, and the double-layer composite film is processed using a laser puncher.

[0025] Bag making: The conditions are the same as those in Example 1, and fresh-keeping bags with an outer size of 30×25 cm, i.e., winter jujube fresh-keeping bags, are prepared. 500 g of winter jujube and a small electronic hygrometer are added into the bag, which is sealed and stored in an environment of 25-30° C. for 5 days, and then taken out to test the quality of the winter jujube.

[0026] Embodiment 3:

[0027] Preparation of ethylene adsorption powder: Ethylene adsorption powder was prepared under the same conditions as in Example 1.

[0028] Preparation of raw material resin for inner layer film: 100 parts of EVA resin and 60 parts of ethylene adsorption powder were put into a high-speed mixer, and other conditions were the same as those in Example 1 to prepare raw material resin for inner layer film.

[0029] Preparation of raw material resin for outer layer film: 100 parts of LDPE resin and 60 parts of EVA resin were put into a high-speed mixer, and other conditions were the same as those in Example 1 to prepare raw material resin for outer layer film.

[0030] Preparation of double-layer composite film: The inner layer screw speed described in Example 1 is adjusted to 28 rpm, and the outer layer screw speed is adjusted to 23 rpm. Other conditions are the same as Example 1, and a double-layer composite film with a thickness of 30 microns is prepared, wherein the inner layer thickness is 18 microns and the outer layer thickness is 12 microns.

[0031] The double-layer composite film is processed using a laser puncher: the conditions are the same as in Example 1, and the double-layer composite film is processed using a laser puncher.

[0032] Bag making: The conditions are the same as those in Example 1, and fresh-keeping bags with an outer size of 30×25 cm, i.e., winter jujube fresh-keeping bags, are prepared. 500 g of winter jujube and a small electronic hygrometer are added into the bag, which is sealed and stored in an environment of 25-30° C. for 5 days, and then taken out to test the quality of the winter jujube.

[0033] Comparative Example 1:

[0034] Buy polyethylene film with a thickness of 50 microns and seal it on three sides to make a fresh-keeping bag with an outer size of 30×25 cm. Add 500 grams of winter jujube and a small electronic hygrometer into the bag. After sealing, store it in an environment of 25-30℃ for 3 days, then take it out to test the quality of the winter jujube.

[0035] Comparative Example 2:

[0036] Purchase 50-micron-thick PET (polyethylene terephthalate) film and seal three sides to make a perforated fresh-keeping bag with an outer dimension of 30×20 cm. Add 500 grams of winter jujube and a small electronic hygrometer into the bag. After sealing, store in an environment of 25-30℃ for 3 days, then take out and test the quality of the winter jujube.

[0037] The quality evaluation method of winter jujube is as follows:

[0038] First, the headspace oxygen and carbon dioxide concentrations in the fresh-keeping bag were tested using a headspace gas analyzer (PAC CHECK 450EC; Mocon, Minneapolis, MN, USA); then the fresh-keeping bag was opened and the relative humidity displayed on the hygrometer was observed; the decay rate of winter jujube was counted; 10 healthy winter jujubes were randomly selected and the hardness of winter jujubes was measured using a FHM-5 fruit hardness analyzer (Takemura Electric Works Co., Ltd., Tokyo, Japan). Ten healthy individuals were randomly selected for each sample, crushed into particles in a grinder, put into a non-woven bag, and squeezed with a juicer to obtain winter jujube juice; 5 drops of the juice were taken with a pipette, and the total soluble solid content (TSS) was measured using a sugar content tester (Atago, Tokyo, Japan, model N-1α) and expressed in %;

[0039] Take about 10g of juice, add 0.5g of 1% starch aqueous solution as an indicator, and titrate with about 0.01M I2-KI (iodine-potassium iodide) aqueous solution until the solution changes from colorless to light blue. Calculate the vitamin (Vc) content in terms of ascorbic acid (mg / 100g) according to formula (2). Resample and test 5 times and take the average value;

[0040] Vc=V×C×152.5×100 / M (2)

[0041] Wherein, V (ml): volume of I2-KI standard solution consumed when titrating sample solution; C (mol / L): molar concentration of I2-KI standard solution; M (g): mass of juice.

[0042] Table 1 Comparison of the quality of winter jujube

[0043]

[0044]

[0045] Table 1 lists the preservation effect of the winter jujube fresh-keeping bag of the present invention on winter jujube. The fresh-keeping bag prepared in the embodiment has the lowest EVA content, the highest LDPE content, the lowest ethylene adsorption powder content, and the lowest laser punching density in the three embodiments, resulting in slightly lower oxygen permeability, carbon dioxide permeability, and water permeability of the fresh-keeping bag, and slightly lower ethylene adsorption capacity and anti-fog capacity. This results in the highest headspace humidity (94%) in the three embodiments after 5 days, effectively preventing water loss, and the humidity in the bag does not rise to the concentration that causes water mist generation and water drop condensation, so there is no mold growth. In Example 1, the lowest oxygen concentration (19%) and the highest carbon dioxide concentration (2.5%), but these atmosphere concentrations still belong to the range of high oxygen concentration and low carbon dioxide concentration, so that the winter jujube is dormant but not anaerobic respiration, which is very suitable for winter jujube preservation. These characteristics make the rot rate of the winter jujube in Example 1 0% after 5 days, there is no odor in the bag, the hardness is 14.5kgf, the sugar content is 24.2%, and the vitamin content is 370mg / 100g. Although Example 1 is the worst among the three examples, it is still much better than the comparative example. The fresh-keeping bag prepared in Example 3 has the highest EVA content, the lowest LDPE content, the highest ethylene adsorption powder content, and the highest laser perforation density among the three examples, resulting in the highest oxygen permeability, carbon dioxide permeability, water permeability, ethylene adsorption capacity, and anti-fog ability among the examples. This results in the lowest headspace humidity (90%) in the fresh-keeping bag. Although the humidity is the lowest in the comparative example, it is still in the appropriate humidity range, which can effectively prevent the winter jujube from losing water. This also results in the highest headspace oxygen concentration (19.8%) and the lowest headspace carbon dioxide concentration (2%). This makes Example 3 the best fresh-keeping effect among all the examples, with a decay rate of 0% after 5 days, the highest hardness among all the examples (15.9kgf), the lowest sugar content among all the examples (23.3%), and the lowest vitamin content among all the examples (323mg / 100g). The various properties and fresh-keeping effects of Example 2 are between Example 1 and Example 3. Generally speaking, the lower the maturity of winter jujube, the lower the sugar content and vitamin content in its flesh, and the higher the hardness. For winter jujube with high maturity, more starch polysaccharides will be converted into soluble sugars, resulting in an increase in sugar content. Increased maturity will also increase the rate of vitamin conversion, resulting in an increase in the vitamin content in the flesh.

[0046] The WVTR (water vapor transmission rate) of the films used in Comparative Examples 1 and 2 is between 2 and 8 g / m 2.day, causing the RH in the bag to far exceed 100%, severe condensation in the bag, high RH causing mold growth, causing about 4% of the winter jujube to rot. In Comparative Example 1, the raw material LDPE was not plasticized by EVA, and the oxygen and carbon dioxide permeability of the film was not large. A lower oxygen concentration (12.7%) and a high carbon dioxide concentration (6.5%) were established. There was some wine-like smell in the fresh-keeping bag, indicating that the high carbon dioxide concentration caused winter jujube poisoning, and the nutritional quality decreased. The hardness, vitamins, and sugar content were all worse than those in the embodiment; Comparative Example 2 used a perforated plastic bag made of PET material. This film had a small WVTR. Even if 12 holes with a diameter of 1 cm were punched on the PET bag, water droplets were still generated inside the bag, indicating that the RH at a position far away from the pores in the PET bag was higher than 100%, and mold growth caused about 3% of the winter jujube to rot. Moreover, since the oxygen and carbon dioxide in the perforated PET bag were the same as those in the air, the respiration rate of the winter jujube could not be slowed down, resulting in a large loss of nutrients.

[0047] It can be seen that the winter jujube fresh-keeping bag prepared by the present invention has the characteristics of high oxygen and carbon dioxide permeability and adjustable water vapor permeability compared with ordinary LDPE or PET bags, and also has the functions of ethylene adsorption and anti-fog (anti-condensation), and can establish a headspace atmosphere with high oxygen concentration and low carbon dioxide concentration and an environment of 90-95% RH, so as to maintain the nutritional quality of winter jujube to the greatest extent.

Claims

1. An ethylene adsorption type laser perforated fresh-keeping bag, characterized in that: It consists of two layers, the inner layer is a blend of EVA (ethylene-vinyl acetate copolymer) and ethylene adsorption powder, and the outer layer is a blend of LDPE (low-density polyethylene) and EVA. The two layers of film are blown out at one time by an AB type film blowing machine, then punched by a laser punching machine, and finally made into bags; the ethylene adsorption powder is aluminum silicate crystals.

2. The ethylene adsorption type laser perforated fresh-keeping bag according to claim 1, characterized in that: The specific preparation method of aluminum silicate crystals includes the following steps: (1) dissolving 100 parts (by weight, the same below) of sodium silicate and 6 parts of anhydrous aluminum nitrate in distilled water respectively, and then mixing the two solutions under stirring and adjusting the pH value to 6 to 6.5 with nitric acid, so that they are complexed in water to form an aluminosilicate gel; (2) evaporating excess water in the aluminosilicate gel by spray drying; (3) calcining at a high temperature of 500°C-600°C to evaporate the crystal water in the aluminosilicate gel, gasify and decompose the nitrate by-product, and generate aluminum silicate crystals, i.e., the corresponding ethylene adsorption powder.

3. The ethylene adsorption type laser perforated fresh-keeping bag according to claim 1, characterized in that: The raw material of the inner layer is made of 100 parts of EVA resin and 40-60 parts of ethylene adsorption powder, which are melted and co-extruded and pelletized, and melted at 145-150°C; The raw material of the outer layer is prepared by adding 40-60 parts of EVA resin to 100 parts of LDPE resin, melting and co-extruding, and pelletizing, and is melted at 145-150°C.

4. The ethylene adsorption type laser perforated fresh-keeping bag according to claim 1, characterized in that: The total film thickness is controlled between 30-50 microns, and the thickness ratio of the inner and outer layers is 40%:60% to 60%:40%.

5. The ethylene adsorption laser perforated fresh-keeping bag according to claim 1, characterized in that: A hole with a diameter of 30-50 microns was made every 0.5-1.5 cm.

6. The method for preparing an ethylene adsorption laser-perforated fresh-keeping bag according to any one of claims 1 to 5, characterized in that: After the inner and outer layers of raw resin are prepared, a double-layer composite film is prepared at 150°C using an AB-type film blowing machine to control the total film thickness and the thickness ratio of the inner and outer layers; then, after the double-layer composite film is blown into shape, a laser puncher is used to punch holes in the film; finally, a bag making machine is used to make bags.

7. Use of the ethylene adsorption laser-perforated fresh-keeping bag according to any one of claims 1 to 5 for preserving winter jujubes.

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