Passive controlled atmosphere fresh-keeping bag as well as preparation method and application thereof

Abstract

The invention discloses a passive controlled atmosphere preservation bag and a preparation method and application thereof, and belongs to the technical field of fruit and vegetable preservation. The preparation method comprises the following steps: mixing low-density polyethylene and an ethylene-vinyl acetate copolymer in proportion, and carrying out melt blending to obtain modified low-density polyethylene resin; the preparation method comprises the following steps: mixing an ethylene-vinyl acetate copolymer, a polyvinyl alcohol swelling material and potassium sorbate in proportion, and carrying out melt blending to obtain modified ethylene-vinyl acetate copolymer resin; preparing a stripe structure film; and processing the fresh-keeping bag into a bag shape to obtain the passive controlled atmosphere fresh-keeping bag. The invention aims to provide the passive controlled atmosphere fresh-keeping bag as well as the preparation method and the application thereof. The passive controlled atmosphere fresh-keeping bag can be used for effectively keeping fresh of fruit and vegetable products with high breathing intensity and keeping the nutritional value and the freshness of the fruit and vegetable products.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a passive atmosphere-controlled fresh-keeping bag and a preparation method and application thereof. Background Art

[0002] Leafy vegetables are prone to water loss and wilt due to their high respiration rate. If water-retaining film is not used, they will lose water in about 5 hours. However, the use of water-retaining film can easily cause vegetables to rot at the mechanically damaged parts. At present, the transportation packaging of leafy vegetables mainly uses polyethylene plastic bags, which contain 10-20 kg of vegetables and 2-5 bottles of ice water to cool the vegetables. Supermarkets mostly use perforated polyethylene terephthalate (PET) plastic bags to preserve freshness under refrigerated conditions. The water vapor transmission rate of these two materials is less than 5g / m 2 .day, resulting in the inability to discharge the moisture produced by the vegetables' respiration in time, causing the relative humidity (RH) in the bag to exceed 100%, which is very likely to cause mold growth.

[0003] The most suitable storage temperature for leafy vegetables is 0 to -5°C and the relative humidity is 95% to 99%. However, the water vapor permeability of polyethylene and PET plastic bags is low and cannot meet this requirement, resulting in frequent rot in damaged parts of vegetables. Although perforated PE and PET plastic bags are put into use on the market, the defects in the physical properties of the film have not been fundamentally solved. Therefore, the development of new leafy vegetable preservation materials and technologies has become an urgent problem to be solved. Summary of the invention

[0004] The present invention aims to provide a passive atmosphere-controlled fresh-keeping bag and a preparation method and application thereof. The passive atmosphere-controlled fresh-keeping bag can effectively preserve fruit and vegetable products with high respiration intensity, thereby maintaining their nutritional value and freshness.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a passive atmosphere-controlled fresh-keeping bag comprises the following steps:

[0007] S1, preparing a modified low-density polyethylene resin: mixing low-density polyethylene and ethylene-vinyl acetate copolymer in proportion, and melt blending to obtain a modified low-density polyethylene resin;

[0008] S2, preparing a modified ethylene-vinyl acetate copolymer resin: mixing ethylene-vinyl acetate copolymer, polyvinyl alcohol swelling material and potassium sorbate in proportion, and melt blending to obtain a modified ethylene-vinyl acetate copolymer resin;

[0009] S3, blowing the prepared modified low-density polyethylene resin and modified ethylene-vinyl acetate copolymer resin through an annular film head with a multi-channel design to obtain a stripe structure film;

[0010] S4, processing the striped structure film into a bag shape to obtain a passive atmosphere-controlled fresh-keeping bag.

[0011] Preferably, the weight ratio of the low-density polyethylene to the ethylene-vinyl acetate copolymer in S1 is 10:1-3.

[0012] Preferably, in the ethylene-vinyl acetate copolymer, the mass percentage of vinyl acetate is 32%.

[0013] Preferably, the mass ratio of the ethylene-vinyl acetate copolymer, the polyvinyl alcohol swelling material and potassium sorbate in S2 is 100:20-30:2-5.

[0014] Preferably, in the ethylene-vinyl acetate copolymer described in S2, the mass percentage of vinyl acetate is 32%.

[0015] Preferably, the method for preparing the polyvinyl alcohol swelling material described in S2 comprises the following steps:

[0016] (1) 40-60 parts of glycerol and 10-20 parts of purified water are mixed evenly, 100 parts of polyvinyl alcohol is added, and the mixture is stirred evenly to obtain a mixture;

[0017] (2) The mixture obtained in step (1) is stored in a sealed state at 35-40° C. for 24 hours and then melt-blended to obtain a polyvinyl alcohol swelling material.

[0018] The invention also provides a passive atmosphere-controlled fresh-keeping bag prepared by the preparation method.

[0019] The present invention also provides a passive atmosphere-controlled fresh-keeping bag prepared by the preparation method or application of the passive atmosphere-controlled fresh-keeping bag in preserving fruits and vegetables.

[0020] Preferably, the fruits and vegetables include leafy vegetables such as rapeseed and spinach, as well as garlic, yam, sweet potato, lily, potato, taro, tomato, chestnut, etc.; winter jujube, peach, pear and other fruits that are sensitive to carbon dioxide.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] The invention discloses a passive atmosphere-controlled fresh-keeping bag and a preparation method and application thereof. The passive atmosphere-controlled fresh-keeping bag can effectively preserve fruit and vegetable products with high respiration intensity, and the oxygen concentration and relative humidity in the fresh-keeping bag are controlled by accurately adjusting the area ratio of a modified low-density polyethylene resin and a modified ethylene-vinyl acetate copolymer resin, thereby significantly extending the fresh-keeping period of vegetables in a high humidity environment of 95% to 99%.

[0023] The modified low-density polyethylene resin has high oxygen and carbon dioxide permeability, while the modified ethylene-vinyl acetate copolymer resin has the function of regulating humidity. Under the joint action, an environment with high oxygen concentration and low carbon dioxide concentration is established in the passive atmosphere-controlled fresh-keeping bag, which effectively slows down the respiration of vegetables and reduces nutrient loss. In addition, by adjusting the width ratio of the stripes, the water vapor permeability can be adjusted, and the humidity in the bag can be effectively controlled to avoid mold growth and condensation caused by excessive humidity. The PVA and potassium sorbate components in the modified ethylene-vinyl acetate copolymer resin provide antibacterial and anti-condensation functions, reduce mold growth on the surface of vegetables, and maintain the freshness of vegetables. After being stored for 3 days, the rapeseed using the fresh-keeping bag of the present invention has a low water loss rate, an almost zero decay rate, and maintains a high soluble solids (TSS), Vc content and chlorophyll content, which is significantly better than traditional materials. The striped fresh-keeping bag of the present invention provides an efficient and economical solution for the preservation of vegetables and fruits, helps to reduce the loss of agricultural products during transportation and storage, and maintains their nutritional value and freshness.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the appearance of the passive atmosphere-controlled fresh-keeping bag provided by the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of the annular membrane head of the present invention;

[0027] Figure 3 The present invention is a structural schematic diagram of a film blowing machine equipped with two single screw conveying devices.

[0028] Description of Reference Numerals

[0029] 1. Melt A (screw A); 2. Melt distributor A; 3. Melt B (screw A); 4. Melt distributor B; 5. Die. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0031] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0032] In the present invention, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in the art and can be purchased through commercial channels.

[0033] Among them, polyvinyl alcohol brand 1799, particle size 100-200 mesh, was purchased from Yinchuan Ningxia Dadi Recycling Development Co., Ltd.;

[0034] Unless otherwise specified, the "parts" described in the present invention are all based on mass parts.

[0035] Embodiment 1 This embodiment provides a passive atmosphere-controlled fresh-keeping bag, and the preparation method comprises the following steps:

[0036] S1. Preparation of modified low-density polyethylene resin: 100 parts of low-density polyethylene and 10 parts of ethylene-vinyl acetate copolymer (the mass percentage of vinyl acetate is 32%) are placed in a high-speed mixer and stirred at 500 rpm for 5 min. The mixture is added to the hopper of a twin-screw extruder, the heating section temperature of the extruder is set to 50-140-140-145-145° C., and melt blended at a screw speed of 100 rpm to obtain a modified low-density polyethylene resin, which is cut into 2-3 mm lengths on a pelletizer to obtain modified low-density polyethylene resin particles;

[0037] S2, preparation of modified ethylene-vinyl acetate copolymer resin:

[0038] (1) 100 parts of polyvinyl alcohol are placed in a high-speed mixer, and a mixed solvent of 40 parts of glycerol and 20 parts of pure water is added dropwise within 10 minutes at a rotation speed of 600 rpm. After the addition is completed, stirring is continued for 5 minutes, and the mixture is taken out and transferred to a polyethylene plastic bag with a thickness of 80 μm. The bag is sealed and stored at an ambient temperature of 35-40° C. for 24 hours to allow the polyvinyl alcohol resin particles to fully swell and reach equilibrium, and the glycerol and water molecules migrate evenly into the interior of the PVA particles. After the polyvinyl alcohol is fully swelled, a polyvinyl alcohol swelling material is obtained.

[0039] (2) 100 parts of ethylene-vinyl acetate copolymer are placed in a high-speed mixer, and 20 parts of polyvinyl alcohol swelling material and 2 parts of potassium sorbate are added at a rotation speed of 300 rpm. After stirring for 5 minutes, the mixture is taken out and transferred to the hopper of a twin-screw extruder. The temperature of the heating section of the extruder is set to 50-140-140-145-145° C., and the mixture is melt-blended at a screw speed of 100 rpm to obtain modified ethylene-vinyl acetate copolymer resin strips, which are cut into 2-3 mm in length on a pelletizer to obtain modified ethylene-vinyl acetate copolymer resin particles.

[0040] S3, set the temperature of the heating section, connector and die head of the two screws of the film blowing machine equipped with two single screw conveying devices to 100-140-145-145-145-145°C, and place the modified low-density polyethylene resin particles in screw A ( Figure 3 ), the modified ethylene-vinyl acetate copolymer resin particles are placed in screw B, the speed of screw A is adjusted to 30rpm, the speed of screw B is adjusted to 25rpm, the blowing ratio of the film bubble is adjusted to 2, the traction ratio is adjusted to 4, the modified resin in screw A is melted to form melt A, which is transformed into strips through melt distributor A, and the modified resin in screw B is melted to form melt B, which is also transformed into strips through melt distributor B. Before exiting the die 5, melt A and melt B are interlaced with each other to form an annular cylindrical film ( Figure 3 ), looking down from the top of the die, you can see Figure 2 As shown in the figure, the melt A and melt B are separated after exiting the die. After cooling the tube film, a striped structure film with a thickness of 50 μm, a width of 5 cm for the modified low-density polyethylene resin stripe A, and a width of 2 cm for the modified ethylene-vinyl acetate copolymer resin stripe B is obtained. Figure 1 , where black is stripe A, white is stripe B, and the total water vapor permeability of the stripe structure film is 20g / m 2 .day, the total oxygen permeability is 2100ml / m 2 .day.atm, the total carbon dioxide permeability is 16000ml / m 2 .day.atm.

[0041] S4. The striped structure film is sealed on three sides to form a passive atmosphere fresh-keeping bag with an outer size of 30×20 cm.

[0042] Embodiment 2 This embodiment provides a passive atmosphere-controlled fresh-keeping bag, and the preparation method is the same as that of Embodiment 1, except that:

[0043] In step S1, the amount of ethylene-vinyl acetate copolymer (the mass percentage of vinyl acetate is 32%) added is 20 parts.

[0044] In step S2, 50 parts of glycerol and 15 parts of purified water are added to (1);

[0045] (2) Add 30 parts of polyvinyl alcohol swelling material and 3 parts of potassium sorbate.

[0046] In step S3, the speed of screw 1 is adjusted to 30 rpm, the speed of screw 2 is adjusted to 50 rpm, the blowing ratio of the film bubble is adjusted to 3, and the pulling ratio is adjusted to 5, to obtain a striped structure film with a thickness of 45 μm, a width of 5 cm for the modified low-density polyethylene resin stripe 1, and a width of 3 cm for the modified ethylene-vinyl acetate copolymer resin stripe 2.

[0047] Among them, the total water vapor permeability of the striped structure film is 40g / m 2 .day, the total oxygen permeability is 2500ml / m 2 .day.atm, the total carbon dioxide permeability is 17000ml / m 2 .day.atm.

[0048] Embodiment 3 This embodiment provides a passive atmosphere-controlled fresh-keeping bag, and the preparation method is the same as that of Embodiment 1, except that:

[0049] In step S1, the amount of ethylene-vinyl acetate copolymer (the mass percentage of vinyl acetate is 32%) added is 30 parts.

[0050] In step S2, 60 parts of glycerol and 10 parts of purified water are added to (1);

[0051] (2) Add 25 parts of polyvinyl alcohol swelling material and 5 parts of potassium sorbate.

[0052] In step S3, the speed of screw 1 is adjusted to 30 rpm, the speed of screw 2 is adjusted to 70 rpm, the blowing ratio of the film bubble is adjusted to 4, and the pulling ratio is adjusted to 6, to obtain a striped structure film with a thickness of 40 μm, a width of 5 cm for the modified low-density polyethylene resin stripe 1, and a width of 5 cm for the modified ethylene-vinyl acetate copolymer resin stripe 2.

[0053] Among them, the total water vapor permeability of the striped structure film is 70g / m 2 .day, the total oxygen permeability is 5000ml / m 2 .day.atm, the total carbon dioxide permeability is 19000ml / m 2 .day.atm.

[0054] Comparative Example 1

[0055] A polyethylene film with a thickness of 50 μm was sealed on three sides to form a fresh-keeping bag with an outer size of 30×20 cm, wherein the polyethylene film was purchased from Hefei Wei Chuang Packaging Materials Co., Ltd.

[0056] Comparative Example 2

[0057] A 50 μm thick BOPP (biaxially oriented polypropylene) film was sealed on three sides to form a fresh-keeping bag with an outer size of 30×20 cm, wherein the BOPP film was purchased from Shenzhen Junmei Packaging Co., Ltd.

[0058] The effects of the fresh-keeping bags provided in Examples 1-3 and Comparative Examples 1-2 were verified by the following tests.

[0059] 500 g of rapeseed and a small electronic hygrometer were added to the fresh-keeping bags provided in Examples 1-3 and Comparative Examples 1-2, respectively. The bags were sealed and stored in an environment of 25-30° C. for 3 days. The rapeseed was then taken out to test its quality.

[0060] The rapeseed quality evaluation method is as follows:

[0061] The headspace O2 and CO2 concentrations in the fresh-keeping bag were tested using a headspace gas analyzer (PAC CHECK 450EC; Mocon, Minneapolis, MN, USA); the fresh-keeping bag was opened and the appearance was observed; the weight loss of the rapeseed was measured using a balance, and the moisture loss rate of the rapeseed was calculated and expressed as a percentage; the weight of the rotten leaves in all the fruit grains was counted and expressed as a percentage; three healthy rapeseeds were randomly selected, and the hardness of the lower tissue of the rapeseed leaves was measured using a FHM-5 fruit hardness analyzer (Takemura Electric Works Co., Ltd., Tokyo, Japan). Three 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 rapeseed 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 as %;

[0062] 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 the following formula, resample and test 5 times, and take the average value;

[0063]

[0064] 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.

[0065] Take 0.1 g rapeseed juice, add 20 ml ethanol, dilute to volume with a 25 ml volumetric flask, and test the chlorophyll A and chlorophyll B contents at 665 and 649 nm respectively using a spectrophotometer. The results are shown in Table 1.

[0066] Table 1 Comparison of rapeseed quality

[0067]

[0068]

[0069] As can be seen from Table 1, the striped film prepared in Example 1 has a larger thickness and a smaller proportion of the water-permeable stripes 2. The prepared fresh-keeping bag has a slightly lower water vapor permeability and oxygen permeability. Therefore, the relative humidity in the fresh-keeping bag is the highest, which is 99%. There is no condensation inside the fresh-keeping bag. After 3 days, the rapeseed has the lowest water loss rate (0.5%), forming an atmosphere with a high oxygen concentration (15%) and a low carbon dioxide atmosphere (1.2%), which effectively prevents water loss and inhibits the possibility of high-humidity mold growth. The rapeseed does not undergo anaerobic respiration, and there is no peculiar smell in the fresh-keeping bag. The rapeseed has a high soluble solid content (TSS) and Vc, and the retention rates of chlorophyll A and chlorophyll B are high.

[0070] The preservation effect of the fresh-keeping bag in Example 2 on rapeseed is similar to that in Example 1.

[0071] The striped film prepared in Example 3 is the thinnest, and the proportion of water-permeable stripes 2 is relatively large. The fresh-keeping bag prepared has a slightly higher water vapor permeability, oxygen permeability and carbon dioxide permeability. Therefore, the relative humidity in the fresh-keeping bag is the lowest (95%), and there is no condensation inside the fresh-keeping bag. After 3 days, the water loss rate of rapeseed is slightly higher than that of Examples 1 and 2 (0.8%). At the same time, a high oxygen concentration (16.9%) and low carbon dioxide atmosphere (1.1%) are also formed, which effectively prevents the loss of water in rapeseed and inhibits the possibility of high-humidity mold growth. Rapeseed does not undergo anaerobic respiration, and there is no peculiar smell in the fresh-keeping bag. The soluble solid content (TSS) and Vc in rapeseed are relatively high, and the retention rate of chlorophyll A and chlorophyll B is high. The potassium sorbate contained in the striped bag effectively kills the mold on the surface of rapeseed in contact with the film, which helps to preserve the freshness of rapeseed.

[0072] The water vapor permeability of the films used in Comparative Examples 1 and 2 is between 2 and 8 g / m 2 .day, causing the relative humidity in the bag to far exceed 100%, severe condensation in the bag, high relative humidity caused the growth of mold, causing about 4% of the rape to rot. In Comparative Example 1, the raw material low-density polyethylene was not plasticized by ethylene-vinyl acetate polymer, 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 odor in the fresh-keeping bag, indicating that the rape had anaerobic respiration, and the rape aged due to anaerobic respiration, and the nutritional quality decreased. The vitamins and TSS embodiments were low, and the rape leaves turned yellow and the chlorophyll content decreased.

[0073] Comparative Example 2 uses a perforated plastic bag made of PET material. This film has a low water vapor permeability, and the relative humidity at a position away from the pores in the PET bag is higher than 100%, so it will still cause about 4% of the leaves to be infected with mold. Moreover, since the oxygen and carbon dioxide in the perforated PET bag are the same as those in the air, the respiration rate of the rapeseed cannot be slowed down, resulting in a large loss of nutrients.

[0074] In summary, the fresh-keeping bag prepared by the present invention has high oxygen and carbon dioxide permeability and water vapor permeability of 20-70g / m 2 It is adjustable between days and has antibacterial and anti-fog (anti-condensation) functions. It can establish a headspace atmosphere with high oxygen concentration and low carbon dioxide concentration and a relative humidity environment of 95%-99%, thereby maintaining the nutritional quality of leafy vegetables with a high exhalation rate to the greatest extent.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a passive atmosphere-controlled fresh-keeping bag, characterized in that: The steps include: S1, preparing a modified low-density polyethylene resin: mixing low-density polyethylene and ethylene-vinyl acetate copolymer in proportion, and melt blending to obtain a modified low-density polyethylene resin; S2, preparing a modified ethylene-vinyl acetate copolymer resin: mixing ethylene-vinyl acetate copolymer, polyvinyl alcohol swelling material and potassium sorbate in proportion, and melt blending to obtain a modified ethylene-vinyl acetate copolymer resin; S3, blowing the prepared modified low-density polyethylene resin and modified ethylene-vinyl acetate copolymer resin through a multi-channel designed annular film head to obtain a stripe structure film; S4, processing the striped structure film into a bag shape to obtain a passive atmosphere-controlled fresh-keeping bag.

2. The preparation method according to claim 1, characterized in that: The weight ratio of the low-density polyethylene to the ethylene-vinyl acetate copolymer in S1 is 10:1-3.

3. The preparation method according to claim 1, characterized in that: The mass ratio of ethylene-vinyl acetate copolymer, polyvinyl alcohol swelling material and potassium sorbate in S2 is 100:20-30:2-5.

4. The preparation method according to claim 1 or 3, characterized in that: The preparation method of the polyvinyl alcohol swelling material in S2 comprises the following steps: (1) 40-60 parts of glycerol and 10-20 parts of purified water are mixed evenly, 100 parts of polyvinyl alcohol is added, and the mixture is stirred evenly to obtain a mixture; (2) The mixture obtained in step (1) is stored in a sealed state at 35-40° C. for 24 hours and then melt-blended to obtain a polyvinyl alcohol swelling material.

5. A passive atmosphere modified fresh-keeping bag prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the passive atmosphere modified fresh-keeping bag prepared by the preparation method according to any one of claims 1 to 4 or the passive atmosphere modified fresh-keeping bag according to claim 5 in preserving fruits and vegetables.

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