Composite degradable modified atmosphere preservative film, preparation and application thereof, and cherry preservation method

Abstract

The invention discloses a composite degradable modified atmosphere preservative film, preparation and application thereof and a cherry preservation method. The preparation method comprises the following steps: mixing copolyester PBTF, poly (butylene adipate-succinate)-terephthalate and a solvent to obtain a film casting solution, pouring the film, and drying to obtain the composite degradable modified atmosphere preservative film. The preservative film has the characteristics of high CO2 permeability and low O2 permeability, and can inhibit respiration of fruits and vegetables and slow down metabolism of the fruits and vegetables, so that the storage time is prolonged, the composite degradable controlled atmosphere preservative film is heat-sealed into a bag and is used for preserving Dalian cherries, and an excellent preservation effect can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of Dalian cherry preservation, and particularly relates to a composite degradable atmosphere-controlled fresh-keeping film and a preparation and application thereof, and a cherry preservation method. Background Art

[0002] Dalian cherries are thick and juicy, not only shiny and bright, but also sweet and sour. Dalian cherries are rich in vitamin C, potassium, iron, etc., which can help enhance immunity, improve cardiovascular health, and play a certain role in the prevention of cancer and diseases related to oxidative stress. With its rich nutritional value and outstanding taste, Dalian cherries have won the favor of many consumers.

[0003] However, Dalian cherries have a thin skin and are full of juice, with delicate internal tissues and extremely high sugar content. Therefore, they are easily invaded by microorganisms and damaged by external mechanical forces, which can easily cause the entire batch of cherries to rot and deteriorate. This situation not only reduces the commercial value of cherries, but also affects their eating experience. At room temperature, the storage time of Dalian cherries generally does not exceed 5 days, and the taste will be affected to a certain extent if it exceeds 3 days. Patent application CN114732047A discloses a method for preserving cherries, but this method requires the use of an immersion method, which requires the cherries to be collected and placed in an immersion solution containing ingredients such as licorice antioxidants, chitosan acetic acid, and glycerol. After being immersed in these ingredients for a period of time, the natural fresh fruity aroma and sweet taste of the cherries may be affected to a certain extent.

[0004] So far, there is no completely effective method for preserving cherries, so a more effective and higher-quality method for preserving cherries is in urgent need of development. Summary of the invention

[0005] Aiming at the disadvantage of poor preservation effect of existing Dalian cherries, the primary purpose of the present invention is to provide a preparation method of a composite degradable modified atmosphere fresh-keeping film.

[0006] Another object of the present invention is to provide a composite degradable modified atmosphere fresh-keeping film prepared by the above method.

[0007] Another object of the present invention is to provide application of the above-mentioned composite degradable modified atmosphere cling film in preserving fruits and vegetables.

[0008] Another object of the present invention is to provide a method for using the above-mentioned composite degradable atmosphere-controlled fresh-keeping film to adjust the atmosphere, humidity, temperature and fresh-keeping of Dalian cherries in a microenvironment. First, nano-acidic bubble water, sodium alginate coating liquid and PP composite degradable atmosphere-controlled film are prepared, a positive ion sterilization device is assembled and an insulation box is made. Then, the Dalian cherries are pre-treated with nano-acidic bubble water, a positive ion sterilization device and a sodium alginate coating liquid, and finally the PP composite degradable atmosphere-controlled film and the insulation box are used to preserve them at room temperature 25±3°C.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing a composite degradable atmosphere-controlled fresh-keeping film comprises the following steps:

[0011] (1) Preparation of copolyester PBTF: Dimethyl furandicarboxylate, catalyst antioxidant and 1,4-butanediol are mixed and heated to obtain a prepolymer poly(2,5-furandicarboxylic acid butylene glycol ester); a catalyst and polytetramethylene ether glycol are then added to the system and the heating reaction is continued, the pressure is reduced, the temperature is increased, and when a climbing pole effect occurs, the reaction is terminated and purified to obtain the copolyester PBTF;

[0012] (2) Preparation of composite degradable modified atmosphere cling film: copolyester PBTF, polybutylene adipate succinate terephthalate (PBAT) and solvent are uniformly mixed to obtain a casting solution, which is then poured and dried to obtain a composite degradable modified atmosphere cling film.

[0013] Preferably, the preparation method of the composite degradable modified atmosphere cling film comprises the following steps:

[0014] (1) Preparation of copolyester PBTF: After dimethyl furandicarboxylate, catalyst antioxidant and 1,4-butanediol are mixed, heated at 90-95°C to react until the liquid is uniform and transparent, then heated to 180-185°C to react until the top of the reaction container exceeds 100°C, and the reaction is continued until the methanol distillate reaches 93% of the theoretical value to obtain a prepolymer poly(2,5-butylene furandicarboxylate) (BHBD); the system temperature is raised to 210-215°C, a catalyst and polytetramethylene ether glycol are added and reacted for 15-20 minutes, then the system pressure is reduced to 80-100 Pa, and the temperature is continued to be raised at a rate of 10-15°C / h. When a climbing pole effect occurs, the reaction is terminated, purified, and the copolyester PBTF is obtained; the reactions are all carried out under an inert gas atmosphere;

[0015] (2) Preparation of composite degradable modified atmosphere cling film: copolyester PBTF, polybutylene adipate succinate terephthalate (PBAT) and solvent are uniformly mixed to obtain a casting solution, which is then poured and dried to obtain a composite degradable modified atmosphere cling film.

[0016] More preferably, in the process of preparing the prepolymer poly-2,5-furandicarboxylic acid butylene glycol ester in step (1), the molar ratio of furandicarboxylic acid dimethyl ester to 1,4-butanediol is (1-5): (8-10); more preferably 5: 9. More preferably, in the process of preparing the prepolymer poly-2,5-furandicarboxylic acid butylene glycol ester in step (1), the molar ratio of furandicarboxylic acid dimethyl ester to antioxidant is (995-1000): (1-5); more preferably 1000: 1.

[0017] More preferably, the antioxidant in step (1) is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (antioxidant 1010) and n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (antioxidant 1076).

[0018] More preferably, in the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to the catalyst is (995-1000):(3-10); more preferably 1000:3; in step (1), the system temperature is raised to 210-215°C, and the molar ratio of the added catalyst to dimethyl furandicarboxylate is (1.5-2.0):(995-1000), more preferably 1.5:1000.

[0019] More preferably, the catalyst in step (1) is at least one of butyl titanate and trimethyl phosphate.

[0020] More preferably, in step (1), the system temperature is raised to 210-215° C., and the mass ratio of the added polytetramethylene ether glycol to the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) is (11-15):(20-25), and more preferably 11:20. More preferably, the molecular weight of the polytetramethylene ether glycol in step (1) is 500-1500.

[0021] More preferably, the reaction in step (1) is carried out under stirring at 400-600 r / min.

[0022] More preferably, the inert gas in step (1) is at least one of argon, helium and nitrogen.

[0023] More preferably, the purification method in step (1) is as follows: after the reaction is completed, the product is quenched with liquid nitrogen, dissolved in chloroform, filtered to remove insoluble matter, and then methanol is added to generate white flocs, which are centrifuged, washed, and dried to obtain purified copolyester PBTF.

[0024] More preferably, the copolyester PBTF in step (2) accounts for 1-5% of the total mass of the copolyester PBTF and polybutylene terephthalate-adipate (PBAT), further preferably 2-5%, and further preferably 2-4%.

[0025] More preferably, the molecular weight of the polybutylene terephthalate-adipate in step (2) is 10,000 to 15,000.

[0026] More preferably, the solvent in step (2) is dichloromethane.

[0027] More preferably, the concentration of the casting solution in step (2) is 15 to 20 wt%.

[0028] The composite degradable atmosphere-controlled fresh-keeping film is prepared by the preparation method.

[0029] The above-mentioned composite degradable modified atmosphere cling film is used in the preservation of fruits and vegetables.

[0030] A method for regulating air, humidity, temperature and freshness of cherries in a microenvironment, comprising the following steps:

[0031] (1) preparing alkaline electrolyzed water with a pH of 8.5 to 9.0, and then acidifying it to a pH of 4.5 to 5.5 to obtain nano acidic bubble water;

[0032] Wash the cherries with nano acidic bubble water, wipe off the surface moisture and set aside;

[0033] (2) placing the cherries from step (1) in a sterilization processor, treating the air with a positive ion generator and then sending the air to the sterilization processor to sterilize the cherries;

[0034] (3) soaking the cherries in step (2) in a sodium alginate coating solution for a period of time and then air-drying;

[0035] (4) heat-sealing the composite degradable atmosphere-controlled fresh-keeping film into a bag, sealing the cherries from step (3) in the composite degradable atmosphere-controlled fresh-keeping bag, and storing them in a constant temperature and humidity environment.

[0036] Preferably, the cherries in step (1) are Dalian cherries.

[0037] Preferably, the alkaline electrolyzed water with a pH of 8.5 to 9.0 in step (1) is obtained by electrolyzing a 1 to 4 wt % NaCl solution.

[0038] Preferably, step (1) is acidified with citric acid to a pH of 4.5 to 5.5.

[0039] Preferably, in step (2), the positive ion generator processes the air for 15 to 20 minutes; and the cherries are sterilized for 5 to 10 minutes.

[0040] Preferably, the concentration of the sodium alginate coating solution in step (3) is 1.5-4 wt %, and is obtained by heating sodium alginate and water until they are completely dissolved and defoamed.

[0041] Preferably, the soaking time in step (3) is 1 to 5 minutes.

[0042] Preferably, the constant temperature and humidity environment in step (4) refers to an environment with a temperature of 25±3° C. and a humidity of 90-95%.

[0043] Preferably, the constant temperature and humidity environment in step (4) is obtained by the following method: holes are opened on each side of the foam insulation box, and a microporous membrane is attached to the holes, bacterial nanocellulose hydrogel is added into the foam insulation box as an insulation layer, and dry ice is placed between the insulation layer and the insulation box wall.

[0044] More preferably, each of the six surfaces of the foam insulation box has 4 to 8 holes with a diameter of 5 to 7 cm; and the pore size of the microporous membrane is 1 to 10 nm.

[0045] More preferably, the bacterial nanocellulose hydrogel is prepared with reference to the paper "Potential of bacterial nanocellulose hydrogel for antipyretic and cooling patches" by Hong Siyi and Wei Bin.

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] (1) The nano acidic bubbles prepared by the present invention can generate a large number of hydroxyl free radicals with strong oxidizing properties when they burst, which can destroy the functional structural parts such as the cell membrane of microorganisms and thus kill the microorganisms. In addition, the microbubbles can fully clean the wrinkles on the surface of the cherry, achieving a full sterilization effect.

[0048] (2) The positive and negative ions generated by the positive ion device assembled in the present invention can neutralize the positive and negative charges in the air, causing changes in the structure of bacteria or energy conversion, thereby achieving a pollution-free and side-effect-free sterilization effect.

[0049] (3) The sodium alginate coating liquid prepared by the present invention can inhibit the respiration of cherries, reduce their nutritional loss, and prevent corruption and deterioration. In addition, sodium alginate is non-toxic and harmless, and the coating components can be removed by simple washing, which will not affect the sensory perception and taste of cherries.

[0050] (4) The PP composite degradable modified atmosphere cling film prepared by the present invention has excellent gas selectivity. Its CO2 / O2 separation coefficient is higher than that of some common packaging film materials, and it has the characteristics of high CO2 permeability and low O2 permeability, which can inhibit the respiration of fruits and vegetables and slow down the metabolism of fruits and vegetables, thereby extending the storage time.

[0051] (6) The PP composite degradable atmosphere-controlled fresh-keeping film prepared by the present invention has degradable properties and can be almost completely degraded in a natural soil environment, thereby reducing environmental pollution.

[0052] (7) The microporous membrane on the foam insulation box of the present invention helps to achieve a moisture permeability effect during the preservation process, thereby preventing excessive moisture in the packaging environment from causing microbial contamination and reducing the quality of fruits and vegetables.

[0053] (8) The structure of bacterial nanocellulose hydrogel gives it excellent water-retention and thermal insulation properties, and this water mainly exists in the form of free water. Since water has a large specific heat capacity, bacterial nanocellulose hydrogel can be used to achieve the purpose of thermal insulation.

[0054] (9) The dry ice in the foam insulation box of the present invention absorbs heat from the environment and sublimates, causing the ambient air temperature to drop, and causing the water vapor in the air to condense quickly to form small water droplets, which plays a role in cooling and moisturizing. At the same time, the CO2 generated by the sublimation of dry ice helps to increase the CO2 content in the packaging environment, forming a high CO2 environment, further inhibiting the aerobic respiration of cherries. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The appearance and morphology of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5;

[0056] Figure 2 The permeability coefficients of CO2 and O2 and the separation coefficients of CO2 / O2 of the PBAT membrane and PP composite degradable gas-controlled membrane prepared in Comparative Example 1 and Examples 1 to 5;

[0057] Figure 3 The test results of the moisture permeability of the PBAT film and PP composite degradable gas-controlled membrane prepared in Comparative Example 1 and Examples 1 to 5;

[0058] Figure 4 The surface contact angles of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5;

[0059] Figure 5 The water absorption and swelling performance test results of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5;

[0060] Figure 6 The mechanical properties test results of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5;

[0061] Figure 7 The light transmittance test results of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5;

[0062] FIG8(a) and FIG8(b) are test results of the degradation performance of the PBAT film and PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1 to 5 in natural soil;

[0063] FIG9(a) and FIG9(b) are test results of the degradation performance of the PBAT membrane and PP composite degradable modified atmosphere membrane prepared in Comparative Example 1 and Examples 1 to 5 in an alkaline (pH=12) solution environment;

[0064] Fig.10 The results are as follows: the quality loss rate of Dalian cherries after 10 days of storage in Comparative Example 1 and Examples 1 to 5;

[0065] Fig.11 The results of determination of soluble solids in Comparative Example 1 and Examples 1 to 5 after 10-day storage of Dalian cherries;

[0066] Fig.12 The results are shown in Table 1, which are the results of determining the vitamin C content of Dalian cherries after 10 days of storage in Comparative Example 1 and Examples 1 to 5. DETAILED DESCRIPTION

[0067] The present invention is further described in detail below in conjunction with examples and drawings, but the embodiments of the present invention are not limited thereto.

[0068] If no specific conditions are specified in the examples of the present invention, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. All raw materials, reagents, etc., whose manufacturers are not specified, are conventional products that can be purchased commercially.

[0069] Example 1

[0070] (1) Preparation of nano acidic bubble water:

[0071] A large electrolysis device is used to adjust the current to the maximum value (13.7A), and a 1wt% NaCl solution is electrolyzed for 20 minutes to prepare alkaline electrolyzed water with a pH of 8.5 to 9.0. The alkaline electrolyzed water is then acidified to a pH of about 5.0 with citric acid. The resulting acidic electrolyzed water is nano acidic bubble water.

[0072] (2) Assembly of sterilization device:

[0073] The model of the positive ion generator is JMH-DC050F(Z)3500S, which is placed on the left side of the sterilization processor to assemble a positive ion sterilization device. The sterilization object - Dalian cherry is placed in the sterilization processor, and the positive ion generator processes the air, and the generated gas flows into the sterilization processor through the rubber tube.

[0074] (3) Preparation of sodium alginate coating solution:

[0075] 1.5 g of sodium alginate was accurately weighed and dissolved in 300 ml of deionized water. The solution was heated in a water bath at about 75° C. and stirred thoroughly until it was completely dissolved. The solution was ultrasonically defoamed for 2 h to obtain a coating solution with a concentration of 1.5 wt %.

[0076] (4) Preparation of copolyester PBTF:

[0077] Weigh 0.05 mol of dimethyl furandicarboxylate and 0.09 mol of 1,4-butanediol, and add 0.2 mol% butyl titanate, 0.1 mol% trimethyl phosphate and 0.1 mol% antioxidant 1010 to a three-necked flask based on the content of dimethyl furandicarboxylate. After sealing, the oxygen in the system is extracted by a vacuum pump, and the pressure is reduced to 0.5 kPa, and maintained for 3 minutes; nitrogen is introduced after the vacuum pump is turned off; the above steps are repeated three times. First heat to 90°C until the liquid is uniform and transparent, then stir at a speed of 480r / min and heat to 180°C. When the top of the reaction vessel exceeds 100°C, continue the reaction for 2 hours, and when the methanol distillate in the receiving bottle below the condenser reaches 93% of the theoretical value, the prepolymer poly 2,5-furandicarboxylic acid butylene glycol ester (BHBD) is obtained. Under nitrogen environment, the temperature was raised to 210°C, butyl titanate with a molar content of 0.15 mol% of dimethyl furandicarboxylate and polytetramethylene ether glycol with a molecular weight of 1000 with a mass fraction of 55% of the prepolymer were added to the system, stirred at a speed of 480r / min, and heated continuously for 15min. Then the system pressure was reduced to 90Pa, and the temperature was continued to rise at a rate of 10°C / h. When the climbing pole effect appeared, the copolyester PBTF was obtained. Quenched with liquid nitrogen, the three-necked flask was broken to take out the block and then vacuum dried. The product was dissolved in chloroform and filtered to remove the insoluble matter. Methanol was added to the mixed solution to produce white flocs. After centrifugation and repeated washing three times, the residual solvent was evaporated at room temperature. It was vacuum dried at 65°C for 12h to obtain the purified copolyester PBTF.

[0078] (5) Preparation of PP composite degradable modified atmosphere fresh-keeping bag:

[0079] The copolyester PBTF and the polybutylene terephthalate adipate (PBAT) with a molecular weight of 10,000 were mixed at a mass ratio of 1:99, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a 1.0% PP composite gas-conditioned cling film, which was heat-sealed into a bag.

[0080] (6) Production of thermal insulation box:

[0081] Six holes with a diameter of 6 cm were opened on each surface of the foam insulation box, and a microporous membrane with a pore size of 5 nm was attached to each hole. Referring to the paper "The Potential of Bacterial Nanocellulose Hydrogel for Antipyretic and Cooling Patch" by Hong Siyi and Wei Bin, 12.5g mannitol, 1.5g tryptone, 2.5g yeast extract, 10g agar, and 500mL of deionized water were used to prepare a slant medium of xylindole acetobacter, and its pH was adjusted to 5.0, and sterilized at 121℃ for 20min for use. And a liquid seed and fermentation medium of xylindole acetobacter were prepared with the same preparation steps as the slant medium of xylindole acetobacter except that agar was not added. Under sterile operation, two loops were picked from the activated strain slant with an inoculation loop and inoculated into 100mL of liquid culture medium. After shaking well, put it in a shake flask incubator and culture it at 30℃ and 160r / min for 12h. The cultured seed liquid was inoculated into the liquid fermentation medium at an inoculation rate of 6% (V / V), and statically cultured at 30°C for 10 days, and a gelatinous bacterial cellulose film was harvested at the interface between the culture medium and the air. The bacterial cellulose film harvested from the static culture was first soaked in a 1% (w / V) NaOH aqueous solution in an 80°C water bath, and then repeatedly rinsed with deionized water until the pH value of the washing liquid was neutral, and then the obtained bacterial cellulose film was cut into 2×4.5cm strips and immersed in a boiling 15% ethanol aqueous solution for 20 minutes, and the bacterial nanocellulose hydrogel was obtained after cooling, and the bacterial nanocellulose hydrogel was added to the incubator as an insulation layer, and dry ice was placed between the insulation layer and the insulation box wall.

[0082] (7) Dalian cherry preservation process:

[0083] Step 1: Select freshly picked Dalian cherries that are uniform in size, free of pests and physical damage, wash them with micro-nano acidic bubble water, drain them, wipe off the surface moisture and set aside.

[0084] Step 2: Place the Dalian cherries to be sterilized into the sterilization device, pre-ventilate for 15 minutes, and then perform positive ion sterilization for 5 minutes.

[0085] Step 3: After positive ion sterilization, immerse the cherries in the pre-prepared sodium alginate coating solution for 1 minute, take them out and air dry them at room temperature.

[0086] Step 4: Immediately seal the air-dried cherries in a PP composite biodegradable modified atmosphere fresh-keeping bag.

[0087] Step 5: Place the fresh-keeping bag containing cherries into a foam insulation box, and then store it in a constant temperature and humidity box at 25±3℃.

[0088] Example 2

[0089] Steps (1) to (4) are the same as steps (1) to (4) in Example 1.

[0090] (5) Preparation of PP composite degradable modified atmosphere fresh-keeping bag:

[0091] The copolyester PBTF and polybutylene terephthalate-adipate (PBAT) with a molecular weight of 10,000 were mixed in a mass ratio of 2:98, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a 2.0% PP composite modified atmosphere cling film, which was heat-sealed into a bag.

[0092] Steps (6) to (7) are the same as steps (6) to (7) in Example 1.

[0093] Example 3

[0094] Steps (1) to (4) are the same as steps (1) to (4) in Example 1.

[0095] (5) Preparation of PP composite degradable modified atmosphere fresh-keeping bag:

[0096] The copolyester PBTF and polybutylene terephthalate adipate (PBAT) with a molecular weight of 10,000 were mixed in a mass ratio of 3:97, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a 3.0% PP composite modified atmosphere cling film, which was heat-sealed into a bag.

[0097] Steps (6) to (7) are the same as steps (6) to (7) in Example 1.

[0098] Example 4

[0099] Steps (1) to (4) are the same as those in Example 1 (1) to (4).

[0100] (5) Preparation of PP composite degradable modified atmosphere fresh-keeping bag:

[0101] The copolyester PBTF and polybutylene terephthalate adipate (PBAT) with a molecular weight of 10,000 were mixed in a mass ratio of 4:96, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a 4.0% PP composite modified atmosphere cling film, which was heat-sealed into a bag.

[0102] Steps (6) to (7) are the same as those in Example 1 (6) to (7).

[0103] Example 5

[0104] Steps (1) to (4) are the same as those in Example 1 (1) to (4).

[0105] (5) Preparation of PP composite degradable modified atmosphere fresh-keeping bag:

[0106] The copolyester PBTF and polybutylene terephthalate adipate (PBAT) with a molecular weight of 10,000 were mixed in a mass ratio of 5:95, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a 5.0% PP composite gas-conditioned cling film, which was heat-sealed into a bag.

[0107] Steps (6) to (7) are the same as those in Example 1 (6) to (7).

[0108] Comparative Example 1

[0109] (1) Preparation of nano acidic bubble water:

[0110] A large electrolysis device is used to adjust the current to the maximum value (13.7A), and a 1wt% NaCl solution is electrolyzed for 20 minutes to prepare alkaline electrolyzed water with a pH of 8.5 to 9.0. The alkaline electrolyzed water is then acidified to a pH of about 5.0 with citric acid. The resulting acidic electrolyzed water is nano acidic bubble water.

[0111] (2) Assembly of sterilization device:

[0112] The model of the positive ion generator is JMH-DC050F(Z)3500S, which is placed on the left side of the sterilization processor to assemble a positive ion sterilization device. The sterilization object - Dalian cherry is placed in the sterilization processor. The positive ion generator processes the air, and the generated gas flows into the sterilization processor through the rubber tube.

[0113] (3) Preparation of sodium alginate coating solution:

[0114] 1.5 g of sodium alginate was accurately weighed and dissolved in 300 ml of deionized water. The solution was heated in a water bath at about 75° C. and stirred thoroughly until it was completely dissolved. The solution was ultrasonically defoamed for 2 h to obtain a coating solution with a concentration of 1.5 wt %.

[0115] (4) Preparation of PBAT fresh-keeping bags:

[0116] Polybutylene terephthalate (PBAT) with a molecular weight of 10,000 was added to dichloromethane solvent to prepare a casting solution with a total concentration of 15.0 wt%, stirred at room temperature for 24 hours, and poured into a film. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 hours to obtain a PBAT cling film, which was then heat-sealed into a bag.

[0117] (5) Production of thermal insulation box:

[0118] Six holes with a diameter of 6 cm were opened on each surface of the foam insulation box, and a microporous membrane with a pore size of 5 nm was attached to each hole. Bacterial nanocellulose hydrogel prepared with reference to the paper "Potential of Bacterial Nanocellulose Hydrogel for Cooling Patch" by Hong Siyi and Wei Bin was added into the insulation box as an insulation layer (same preparation process as in Example 1), and dry ice was placed between the insulation layer and the insulation box wall.

[0119] (6) Dalian cherry preservation process:

[0120] Step 1: Select freshly picked Dalian cherries that are uniform in size, free of pests and physical damage, wash them with micro-nano acidic bubble water, drain them, wipe off the surface moisture and set aside.

[0121] Step 2: Place the Dalian cherries to be sterilized into the sterilization device, pre-ventilate for 15 minutes, and then perform positive ion sterilization for 5 minutes.

[0122] Step 3: After positive ion sterilization, immerse the cherries in the pre-prepared sodium alginate coating solution for 1 minute, take them out and air dry them at room temperature.

[0123] Step 4: Immediately seal the air-dried cherries in a controlled atmosphere fresh-keeping bag.

[0124] Step 5: Place the fresh-keeping bag containing cherries into a foam insulation box, and then store it in a constant temperature and humidity box at 25±3℃.

[0125] 1. Determination of vitamin C content:

[0126] 1. Make a standard curve

[0127] Table 1

[0128]

[0129] Take 7 test tubes, number them, add various solutions according to the table above (Table 1), place the mixed solution at 30°C for 60 minutes, and then use the mixed solution in test tube No. 0 as a reference to measure the absorbance value at a wavelength of 534nm. Draw a standard curve with micrograms of ascorbic acid as the horizontal axis and the absorbance value as the vertical axis to obtain the linear regression equation.

[0130] 2. Extraction

[0131] Weigh 10.0 g of pulp sample into a mortar, add 20 mL of 5% TCA solution, grind into a slurry under ice bath conditions, transfer to a 100 mL volumetric flask, and dilute to the mark with 5% TCA solution. After mixing and extracting for 10 minutes, filter and collect the filtrate for later use.

[0132] 3. Determination

[0133] Take 1.0mL of sample extract in a test tube, add 1.0ml of 5% TCA solution, and then add other components in the same way as the standard curve, react and measure. Record the absorbance value of the reaction system at a wavelength of 534nm. Repeat three times.

[0134] 4. Experimental results and calculations

[0135] According to the absorbance value, find the micrograms of ascorbic acid in the corresponding mixed solution on the standard curve, and calculate the ascorbic acid content in the fruit and vegetable tissues according to the following formula. The ascorbic acid content in fruits and vegetables is expressed as milligrams of ascorbic acid contained in 100g fresh weight (FW) sample, that is, mg / 100gFW. Calculation formula:

[0136] Ascorbic acid content mg / 100gFW=[(V×C) / (Vs×W×1000)]×100

[0137] Where: C—micrograms of ascorbic acid obtained from the standard curve, μg;

[0138] Vs—volume of sample extract used during titration, mL;

[0139] V—total volume of sample extract, mL;

[0140] W—sample weight, g.

[0141] 2. Determination of weight loss rate:

[0142] Use an electronic balance to weigh the initial weight of the sample, then weigh it at regular intervals, and calculate the weight loss rate according to the following formula:

[0143] Weight loss rate (%) = (m1-m2) / m1×100%

[0144] Where: m1—initial mass, g;

[0145] m2—mass on the day of measurement, g.

[0146] 3. Determination of soluble solids

[0147] Randomly select 3-4 Dalian cherries from each treatment group, peel and pit them, extract the pulp and squeeze the juice, centrifuge at 8000r / min for 10min, and take the supernatant for later use. Use sugar meter PAL-108 to measure the soluble solid content.

[0148] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a composite degradable modified atmosphere cling film, characterized in that: The following steps are involved: (1) Preparation of copolyester PBTF: Dimethyl furandicarboxylate, catalyst antioxidant and 1,4-butanediol are mixed and heated to obtain a prepolymer poly(2,5-furandicarboxylic acid butylene glycol ester); a catalyst and polytetramethylene ether glycol are then added to the system and the heating reaction is continued, the pressure is reduced, the temperature is increased, and when a climbing pole effect occurs, the reaction is terminated and purified to obtain the copolyester PBTF; (2) Preparation of composite degradable modified atmosphere cling film: copolyester PBTF, polybutylene adipate succinate-terephthalate and solvent are uniformly mixed to obtain a casting solution, which is then poured and dried to obtain a composite degradable modified atmosphere cling film.

2. The method for preparing a composite degradable modified atmosphere cling film according to claim 1, characterized in that: The following steps are involved: (1) Preparation of copolyester PBTF: After dimethyl furandicarboxylate, catalyst antioxidant and 1,4-butanediol are mixed, heated to 90-95°C for reaction until the liquid is uniform and transparent, then heated to 180-185°C for reaction until the top of the reaction container exceeds 100°C, and the reaction is continued until the methanol distillate reaches 93% of the theoretical value to obtain a prepolymer poly(2,5-furandicarboxylic acid butylene glycol); the system temperature is raised to 210-215°C, a catalyst and polytetramethylene ether glycol are added and reacted for 15-20 minutes, then the system pressure is reduced to 80-100 Pa, and the temperature is continued to be raised at a rate of 10-15°C / h. When a climbing pole effect occurs, the reaction is terminated, purified, and the copolyester PBTF is obtained; the reactions are all carried out under an inert gas atmosphere; (2) Preparation of composite degradable modified atmosphere cling film: copolyester PBTF, polybutylene adipate succinate-terephthalate and solvent are uniformly mixed to obtain a casting solution, which is then poured and dried to obtain a composite degradable modified atmosphere cling film.

3. The method for preparing a composite degradable modified atmosphere cling film according to claim 1, characterized in that: In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to 1,4-butanediol is (1-5):(8-10); In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to the antioxidant is (995-1000): (1-5); In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to the catalyst is (995-1000): (3-10); In step (1), the system temperature is raised to 210-215° C., the molar ratio of the added catalyst to dimethyl furandicarboxylate is (1.5-2.0):(995-1000), and the mass ratio of polytetramethylene ether glycol to prepolymer poly(2,5-furandicarboxylic acid butylene glycol) is (11-15):(20-25); The antioxidant in step (1) is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; The catalyst in step (1) is at least one of butyl titanate and trimethyl phosphate; The molecular weight of the polytetramethylene ether glycol in step (1) is 500-1500.

4. The method for preparing a composite degradable modified atmosphere cling film according to claim 1, characterized in that: The copolyester PBTF in step (2) accounts for 1 to 5% of the total mass of the copolyester PBTF and polybutylene terephthalate-adipate; The molecular weight of the polybutylene terephthalate-adipate in step (2) is 10000 to 15000; The concentration of the casting solution in step (2) is 15-20wt%.

5. The method for preparing a composite degradable modified atmosphere cling film according to claim 1, characterized in that: In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to 1,4-butanediol is 5:9; In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to the antioxidant is 1000:1; In the preparation process of the prepolymer poly(2,5-furandicarboxylic acid butylene glycol) in step (1), the molar ratio of dimethyl furandicarboxylate to the catalyst is 1000:3; In step (1), the system temperature is raised to 210-215° C., the molar ratio of the added catalyst to dimethyl furandicarboxylate is 1.5:1000; the mass ratio of polytetramethylene ether glycol to prepolymer poly(2,5-furandicarboxylic acid butylene glycol) is 11:20; The inert gas in step (1) is at least one of argon, helium and nitrogen; The copolyester PBTF in step (2) accounts for 2-5% of the total mass of the copolyester PBTF and polybutylene terephthalate-adipate (PBAT).

6. A composite degradable modified atmosphere fresh-keeping film prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the composite degradable modified atmosphere cling film according to claim 6 in preserving fruits and vegetables.

8. A method for regulating air, humidity, temperature and freshness of cherries in a microenvironment, characterized in that: The following steps are involved: (1) preparing alkaline electrolyzed water with a pH of 8.5 to 9.0, and then acidifying it to a pH of 4.5 to 5.5 to obtain nano acidic bubble water; Wash the cherries with nano acidic bubble water, wipe off the surface moisture and set aside; (2) placing the cherries from step (1) in a sterilization processor, treating the air with a positive ion generator and then sending the air to the sterilization processor to sterilize the cherries; (3) soaking the cherries in step (2) in a sodium alginate coating solution for a period of time and then air-drying; (4) Heat-seal the composite degradable modified atmosphere fresh-keeping film according to claim 6 into a bag, seal the cherries from step (3) in the composite degradable modified atmosphere fresh-keeping bag, and store them in a constant temperature and humidity environment.

9. The method for maintaining freshness of cherries by regulating air, humidity and temperature in a microenvironment according to claim 8, characterized in that: The cherries in step (1) are Dalian cherries; The alkaline electrolyzed water with a pH of 8.5 to 9.0 in step (1) is obtained by electrolyzing a 1 to 4 wt% NaCl solution; Step (1) acidifying with citric acid to a pH of 4.5 to 5.5; In step (2), the positive ion generator processes the air for 15 to 20 minutes; the Dalian cherries are sterilized for 5 to 10 minutes; The concentration of the sodium alginate coating solution in step (3) is 1.5-4 wt %, and is obtained by heating sodium alginate and water until they are completely dissolved and defoamed; The soaking time in step (3) is 1 to 5 minutes; The constant temperature and humidity environment in step (4) refers to an environment with a temperature of 25±3°C and a humidity of 90-95%; The constant temperature and humidity environment in step (4) is obtained by the following method: holes are opened on each side of the foam insulation box, and microporous membranes are attached to the holes, bacterial nanocellulose hydrogel is added into the foam insulation box as an insulation layer, and dry ice is placed between the insulation layer and the insulation box wall.

10. The method for maintaining freshness of cherries by regulating air, humidity and temperature in a microenvironment according to claim 9, characterized in that: The six surfaces of the foam insulation box are each provided with 4 to 8 holes with a diameter of 5 to 7 cm; the pore diameter of the microporous membrane is 1 to 10 nm.

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