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

Abstract

The application discloses a kind of composite degradable modified atmosphere fresh-keeping film and its preparation, application and cherry preservation method.The application obtains casting film liquid by mixing copolyester PBTF, polybutylene succinate-terephthalate and solvent, pours film, drying, obtains composite degradable modified atmosphere fresh-keeping film.The fresh-keeping film has the characteristics of high CO2 and low O2 permeability, can inhibit fruit and vegetable respiration, slow down fruit and vegetable metabolism, thereby prolong storage time, the composite degradable modified atmosphere fresh-keeping film is heat sealed into bag and used for preserving Dalian cherry, and excellent preservation effect can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of Dalian cherry preservation, and particularly relates to a composite degradable modified atmosphere preservation film and a preparation method and application thereof and a cherry preservation method. BACKGROUND

[0002] The fruit of Dalian cherry is thick and juicy, not only bright and shiny in appearance, but also sweet and sour in taste. Dalian cherry is rich in vitamin C, potassium, iron and the like, is helpful to enhance immunity and improve cardiovascular health, and has a certain effect on the prevention of cancer and diseases related to oxidative stress. With its rich nutritional value and outstanding taste, Dalian cherry has won the favor of many consumers.

[0003] However, the fruit of Dalian cherry is thin-skinned and full of juice, the internal tissue is relatively delicate, and the sugar content is also extremely high, so it is easy to be invaded by microorganisms and damaged by external mechanical force, thereby easily leading to the spoilage of the whole batch of cherries. This condition not only reduces the commodity value of cherries, but also affects its eating experience. The storage time of Dalian cherry at room temperature is generally not more than 5 days, and the taste will be affected to a certain extent generally more than 3 days. Patent application CN114732047A discloses a cherry preservation method, but the method needs to use the soaking method, and needs to place the cherries collected in the soaking liquid containing licorice antioxidant, chitosan acetic acid, glycerol and the like after soaking in these components for a period of time, which may affect the natural fresh fruit aroma and sweet taste of cherries to a certain extent.

[0004] So far, there is no completely effective cherry preservation method, and therefore, a more effective and high-quality cherry preservation method is urgently needed to be developed. SUMMARY

[0005] In view of the poor preservation effect of existing Dalian cherries, the primary purpose of the present application is to provide a preparation method of a composite degradable modified atmosphere preservation film.

[0006] Another purpose of the present application is to provide a composite degradable modified atmosphere preservation film prepared by the above method.

[0007] Still another purpose of the present application is to provide the application of the above composite degradable modified atmosphere preservation film in fruit and vegetable preservation.

[0008] Another purpose of the present application is to provide a method for micro-environment conditioning, humidity conditioning, cooling and preservation of Dalian cherries using the above-mentioned composite degradable modified atmosphere packaging film. First, prepare nano-acidic bubble water, sodium alginate coating liquid and PP composite degradable modified atmosphere packaging film, assemble a positive ion sterilization device and make a heat preservation box. Then, pretreat the Dalian cherries with nano-acidic bubble water, a positive ion sterilization device and sodium alginate coating liquid, and finally use the PP composite degradable modified atmosphere packaging film and the heat preservation box for preservation at room temperature of 25±3℃.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] A preparation method of a composite degradable modified atmosphere packaging film, comprising the following steps:

[0011] (1) Preparation of copolyester PBTF: after furandicarboxylic acid dimethyl ester, catalyst antioxidant and 1,4-butanediol are mixed, heating reaction is performed to obtain a prepolymer polybutylene 2,5-furandicarboxylate; then catalyst and polytetramethylene ether glycol are added to the system and heating reaction is continued, the pressure is reduced, the temperature is increased, and when the climbing rod effect appears, the reaction is ended, and purification is performed to obtain copolyester PBTF;

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

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

[0014] (1) Preparation of copolyester PBTF: after furandicarboxylic acid dimethyl ester, catalyst antioxidant and 1,4-butanediol are mixed, heating reaction is performed to obtain a prepolymer polybutylene 2,5-furandicarboxylate; then catalyst and polytetramethylene ether glycol are added to the system and heating reaction is continued, the pressure is reduced, the temperature is increased, and when the climbing rod effect appears, the reaction is ended, and purification is performed to obtain copolyester PBTF;

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

[0016] More preferably, in the preparation of the prepolymer polybutylene-2,5-furandicarboxylate in step (1), the molar ratio of dimethyl furandicarboxylate to 1,4-butanediol is (1-5):(8-10); more preferably, 5:9. More preferably, in the preparation of the prepolymer polybutylene-2,5-furandicarboxylate in step (1), the molar ratio of dimethyl furandicarboxylate to antioxidant is (995-1000):(1-5); more preferably, 1000:1.

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

[0018] More preferably, in the preparation of the prepolymer polybutylene-2,5-furandicarboxylate in step (1), the molar ratio of dimethyl furandicarboxylate to catalyst is (995-1000):(3-10); more preferably, 1000:3; and the molar ratio of the catalyst to dimethyl furandicarboxylate added in step (1) when the system temperature is raised to 210-215°C 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 mass ratio of polytetramethylene ether glycol to the prepolymer polybutylene-2,5-furandicarboxylate added when the system temperature is raised to 210-215°C is (11-15):(20-25); 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 dissolved in chloroform after quenching with liquid nitrogen, and insoluble substances are removed by filtration, then methanol is added to generate white flocculent substances, which are separated by centrifugation and washed, and dried to obtain the purified copolyester PBTF.

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

[0025] More preferably, the polybutylene adipate terephthalate has a molecular weight of 10,000-15,000.

[0026] More preferably, the solvent is dichloromethane.

[0027] More preferably, the concentration of the casting solution is 15-20 wt%.

[0028] The above preparation method produces a composite degradable modified atmosphere packaging film.

[0029] The above composite degradable modified atmosphere packaging film is used for fruit and vegetable preservation.

[0030] A method for cherry microenvironment conditioning, humidification and cooling preservation, comprising the following steps:

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

[0032] Washing the cherries with the nano-acidic bubble water and wiping off the surface moisture for standby;

[0033] (2) placing the cherries of step (1) in a sterilization processor, and sending the air treated by the positive ion generator into the sterilization processor to sterilize the cherries;

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

[0035] (4) heat-sealing the above composite degradable modified atmosphere packaging film into a bag, sealing the cherries of step (3) in the composite degradable modified atmosphere packaging bag, and storing in a constant temperature and humidity environment.

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

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

[0038] Preferably, the pH of 4.5-5.5 of step (1) is acidified by citric acid.

[0039] Preferably, the air treated by the positive ion generator of step (2) is for 15-20 min, and the sterilization time of the cherries is 5-10 min.

[0040] Preferably, the concentration of the sodium alginate coating solution in step (3) is 1.5-4wt%, which is obtained by heating sodium alginate and water to complete dissolution and defoaming.

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

[0042] Preferably, the constant temperature and humidity environment in step (4) refers to an environment with a temperature of 25±3℃ 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 microporous membranes are attached to the holes; bacterial nanocellulose hydrogel is added as a heat preservation layer in the foam insulation box, and dry ice is placed between the heat preservation layer and the wall of the foam insulation box.

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

[0045] More preferably, the bacterial nanocellulose hydrogel is prepared according to the paper "Potential of bacterial nanocellulose hydrogel for fever-reducing cooling patches" by Hong Siyi and Wei Bin.

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

[0047] (1) The nanometer acidic bubbles prepared by the present application can generate a large amount of hydroxyl radicals with strong oxidizing properties when they break, which can destroy the functional structural parts such as the cell membrane of microorganisms, thereby killing the microorganisms, and the microbubbles can fully clean the wrinkles on the surface of the cherries, achieving the effect of full sterilization.

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

[0049] (3) The sodium alginate coating solution prepared by the present application can inhibit the respiration of cherries, reduce the loss of nutrients, and prevent spoilage. Moreover, sodium alginate is non-toxic and harmless, and the coating components can be removed simply by washing, without affecting the sensory and taste of cherries.

[0050] (4) The PP composite degradable modified atmosphere packaging film prepared by the present application 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 prolonging the storage time.

[0051] (6) The PP composite degradable modified atmosphere preservation film prepared by the application has degradable performance, can be almost fully degraded in a natural soil environment, and reduces environmental pollution.

[0052] (7) The microporous film on the foam insulation box of the application helps the moisture permeability effect in the preservation process, avoids excessive moisture in the packaging environment, causes microbial contamination, and reduces the quality of fruits and vegetables.

[0053] (8) The structure of the bacterial nanocellulose hydrogel makes it have excellent water holding performance and heat insulation performance, and the water mainly exists in the form of free water. Since the specific heat capacity of water is large, the purpose of heat preservation can be achieved through the bacterial nanocellulose hydrogel.

[0054] (9) The dry ice in the foam insulation box of the application absorbs heat from the environment to sublimate, causing the temperature of the surrounding air to drop, and causing the water vapor in the air to rapidly condense to form small water droplets, thereby achieving the effects of cooling and moisturizing. At the same time, the CO2 produced by the sublimation of dry ice helps to increase the CO2 content in the packaging environment, forming a high-CO2 environment, which further inhibits the aerobic respiration of cherries. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 The appearance of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 is shown in the following table:

[0056] Figure 2 The CO2, O2 permeability coefficients and CO2 / O2 separation coefficients of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 are shown in the following table:

[0057] Figure 3 The moisture permeability test results of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 are shown in the following table:

[0058] Figure 4 The surface contact angle of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 is shown in the following table:

[0059] Figure 5 The water absorption and swelling performance test results of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 are shown in the following table:

[0060] Figure 6 The mechanical property test results of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 are shown in the following table:

[0061] Figure 7 The light transmittance test results of the PBAT film and the PP composite degradable modified atmosphere film prepared in Comparative Example 1 and Examples 1-5 are shown in the following table:

[0062] Fig. 8(a) and Fig. 8(b) are test results of PBAT film, PP composite degradable modified atmosphere film prepared by Comparative Example 1 and Examples 1-5 in natural soil degradation performance;

[0063] Fig. 9(a) and Fig. 9(b) are test results of PBAT film, PP composite degradable modified atmosphere film prepared by Comparative Example 1 and Examples 1-5 in alkaline (pH = 12) solution environment degradation performance;

[0064] Figure 10 Fig. 10 is a determination result of quality loss rate of Dalian cherries preserved for 10 days by Comparative Example 1 and Examples 1-5;

[0065] Figure 11 Fig. 11 is a determination result of soluble solids of Dalian cherries preserved for 10 days by Comparative Example 1 and Examples 1-5;

[0066] Figure 12 Fig. 12 is a determination result of vitamin C content of Dalian cherries preserved for 10 days by Comparative Example 1 and Examples 1-5. DETAILED DESCRIPTION

[0067] The present application will be described in further detail by embodiments and drawings, but the embodiments of the present application are not limited thereto.

[0068] The specific conditions not mentioned in the embodiments of the present application are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. used without mentioning the manufacturer are all conventional products that can be purchased on the market.

[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 (13.7 A), and 1 wt% NaCl solution is electrolyzed for 20 min to prepare alkaline electrolytic water with pH 8.5-9.0. Then the alkaline electrolytic water is acidified to pH about 5.0 by citric acid, and the obtained acidic electrolytic water is nano-acidic bubble water.

[0072] (2) Assembly of sterilization device:

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

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

[0075] Accurately weigh 1.5 g of sodium alginate into 300 ml of deionized water, heat in water bath at about 75℃, fully stir until completely dissolved, ultrasonic defoaming for 2 h to prepare a solution with a concentration of 1.5 wt% coating solution.

[0076] (4) Preparation of copolyester PBTF:

[0077] Accurately weigh 0.05 mol of dimethyl furan dicarboxylate and 0.09 mol of 1,4-butanediol, and based on the content of dimethyl furan dicarboxylate, add 0.2 mol% of butyl titanate, 0.1 mol% of trimethyl phosphate and 0.1 mol% of antioxidant 1010 in a three-necked flask. After sealing, the oxygen in the system is pumped out by vacuum pump, the pressure is reduced to 0.5 kPa, and maintained for 3 min; after closing the vacuum pump, nitrogen is introduced; the above steps are repeated three times. First heat to 90℃, until the liquid is uniform and transparent, then stir at a speed of 480 r / min, and heat to 180℃. When the temperature at the top of the reaction vessel exceeds 100℃, continue to react for 2 h, and when the methanol distillate in the receiving bottle below the condenser reaches 93% of the theoretical value, the prepolymer polybutylene glycol 2,5-furan dicarboxylate (BHBD) is obtained. Under nitrogen environment, the temperature is raised to 210℃, 0.15 mol% of butyl titanate based on the content of dimethyl furan dicarboxylate and 55% of the prepolymer by mass fraction of polytetramethylene ether glycol with a molecular weight of 1000 are added to the system, and stirring is carried out at a speed of 480 r / min, and heating is continued for 15 min. The pressure of the system is then reduced to 90 Pa, and the temperature is continued to rise at a rate of 10℃ / h. When the climbing rod effect appears, the copolyester PBTF is obtained. Quenching with liquid nitrogen, breaking the three-necked flask to take out the block, and then vacuum drying. Dissolve the product in chloroform, filter out the insoluble material. Add methanol to the mixed solution to produce white flocculent material. Centrifugal separation and repeated washing three times, evaporation of residual solvent at room temperature. Vacuum drying at 65℃ for 12 h to obtain purified copolyester PBTF.

[0078] (5) Preparation of PP composite degradable modified atmosphere packaging bag:

[0079] Mix copolyester PBTF and polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 at a mass ratio of 1:99, and add dichloromethane solvent to prepare a casting solution with a total concentration of 15.0 wt%. Stir at room temperature for 24 h, and pour the film. After the solvent evaporates, the film is dried in a vacuum drying oven for 24 h to obtain a 1.0% PP composite modified atmosphere film, and heat sealed into a bag.

[0080] (6) Preparation of incubator:

[0081] Six holes with a diameter of 6 cm were opened on each side of the foam incubator, and a microporous membrane with a pore size of 5 nm was attached to each hole. According to the paper by Hong Siyi and Wei Bin, “Potential of bacterial nanocellulose hydrogel for fever-reducing patches”, a 12.5 g of mannitol, 1.5 g of tryptone, 2.5 g of yeast extract, 10 g of agar, and 500 mL of deionized water were used to prepare a gluconacetobacter xylinus slant medium, and the pH was adjusted to 5.0, which was sterilized at 121℃ for 20 min for use. A gluconacetobacter xylinus liquid seed and fermentation medium were prepared in the same way as the gluconacetobacter xylinus slant medium, except that no agar was added. Under sterile conditions, two loops of activated bacterial strain were picked up from the slant medium and inoculated into 100 mL of liquid medium. After shaking, the mixture was placed in a shaking incubator at 30℃ and 160 r / min for 12 h. The seed liquid was inoculated into the liquid fermentation medium at a concentration of 6% (V / V), and the mixture was incubated at 30℃ for 10 days. The gel-like bacterial cellulose membrane was harvested at the interface between the culture medium and the air. The bacterial cellulose membrane was first soaked in 1% (w / V) NaOH solution at 80℃, then washed with deionized water until the pH of the washing solution was neutral. Then the bacterial cellulose membrane was cut into 2×4.5 cm strips and immersed in boiling 15% ethanol solution for 20 min. After cooling, the bacterial nanocellulose hydrogel was obtained. The bacterial nanocellulose hydrogel was added to the foam incubator as a heat preservation layer, and dry ice was placed between the heat preservation layer and the wall of the foam incubator.

[0082] (7) Preservation process of Dalian cherries:

[0083] Step 1: Freshly picked Dalian cherries with uniform size, no insect damage, and no physical trauma were washed with micro-nano acidic bubble water, drained, and surface moisture was wiped off for standby.

[0084] Step 2: The sterilization object Dalian cherry was placed in the sterilization device, pre-aerated for 15 min, and then subjected to positive ion sterilization for 5 min.

[0085] Step 3: After positive ion sterilization, the cherries were immersed in the pre-prepared sodium alginate coating solution for 1 min, and then dried at room temperature.

[0086] Step 4: The dried cherries were immediately sealed in a PP composite degradable modified atmosphere packaging bag.

[0087] Step 5: The preservation bag containing the cherries was placed in a foam incubator, and then placed in a constant temperature and humidity incubator at 25±3℃ for storage.

[0088] Example 2

[0089] Steps (1)-(4) are the same as steps (1)-(4) of Example 1.

[0090] (5) Preparation of PP composite degradable modified atmosphere packaging bags:

[0091] The copolyester PBTF and polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 were mixed in a mass ratio of 2:98, dichloromethane solvent was added, and a casting solution with a total concentration of 15.0wt% was prepared. After stirring at room temperature for 24h, the film was poured. After the solvent volatilized, the film was dried in a vacuum drying oven for 24h to obtain 2.0% PP composite modified atmosphere packaging film, and heat sealed into bags.

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

[0093] Example 3

[0094] Steps (1)-(4) are the same as steps (1)-(4) of Example 1.

[0095] (5) Preparation of PP composite degradable modified atmosphere packaging bags:

[0096] The copolyester PBTF and polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 were mixed in a mass ratio of 3:97, dichloromethane solvent was added, and a casting solution with a total concentration of 15.0wt% was prepared. After stirring at room temperature for 24h, the film was poured. After the solvent volatilized, the film was dried in a vacuum drying oven for 24h to obtain 3.0% PP composite modified atmosphere packaging film, and heat sealed into bags.

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

[0098] Example 4

[0099] Steps (1)-(4) are the same as steps (1)-(4) of Example 1.

[0100] (5) Preparation of PP composite degradable modified atmosphere packaging bags:

[0101] The copolyester PBTF and polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 were mixed in a mass ratio of 4:96, dichloromethane solvent was added, and a casting solution with a total concentration of 15.0wt% was prepared. After stirring at room temperature for 24h, the film was poured. After the solvent volatilized, the film was dried in a vacuum drying oven for 24h to obtain 4.0% PP composite modified atmosphere packaging film, and heat sealed into bags.

[0102] Steps (6)-(7) are the same as steps (6)-(7) of Example 1.

[0103] Example 5

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

[0105] (5) Preparation of PP composite degradable modified atmosphere packaging bag:

[0106] The copolyester PBTF and polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 were mixed at a mass ratio of 5:95, and dichloromethane solvent was added to prepare a casting solution with a total concentration of 15.0wt%. The solution was stirred at room temperature for 24h, and then poured into a film. After the solvent was volatilized, the film was placed in a vacuum drying oven for 24h to obtain a 5.0% PP composite modified atmosphere packaging film, which was heat sealed into a bag.

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

[0108] Comparative Example 1

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

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

[0111] (2) Assembly of sterilization device:

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

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

[0114] 1.5g of sodium alginate was accurately weighed and dissolved in 300ml of deionized water. The solution was heated in a water bath at about 75℃ with stirring until completely dissolved, and then ultrasonic defoaming was performed for 2h to obtain a coating solution with a concentration of 1.5wt%.

[0115] (4) Preparation of PBAT preservation bag:

[0116] Polybutylene adipate terephthalate (PBAT) with a molecular weight of 10000 was added to dichloromethane solvent to prepare a casting solution with a total concentration of 15.0wt%. The solution was stirred at room temperature for 24h, and then poured into a film. After the solvent was volatilized, the film was placed in a vacuum drying oven for 24h to obtain a PBAT preservation film, which was heat sealed into a bag.

[0117] (5) Preparation of incubator:

[0118] Six holes with a diameter of 6 cm were opened on each side of the foam insulation box, and a microporous membrane with a pore size of 5 nm was attached to each hole. The bacterial nanocellulose hydrogel prepared according to the method described in the paper by Hong Siyi and Wei Bin, Potential of bacterial nanocellulose hydrogel for fever-reducing patches, was added to 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 wall of the insulation box.

[0119] (6) Preservation process of Dalian cherries:

[0120] Step 1: Select fresh and evenly sized Dalian cherries that are free of pests and physical trauma. Wash the cherries with micro-nano acidic bubble water, drain and dry the surface moisture for use.

[0121] Step 2: Place the sterilization object Dalian cherries in the sterilization device, pre-ventilate for 15 min, and then perform positive ion sterilization treatment for 5 min.

[0122] Step 3: After positive ion sterilization, immerse the cherries in the pre-configured sodium alginate coating solution for 1 min, and then dry at room temperature.

[0123] Step 4: Immediately seal the dried cherries in a modified atmosphere preservation bag.

[0124] Step 5: Place the preservation bag containing the cherries in a foam insulation box, and then place it in a constant temperature and humidity box at 25±3℃ for storage.

[0125] I. Determination of Vitamin C content:

[0126] 1. Preparation of standard curve

[0127] Table 1

[0128]

[0129] Take 7 test tubes, number them, and add various solutions according to the above table (Table 1). Place the mixed solution in a 30℃ environment for 60 min. Then, at a wavelength of 534 nm, measure the absorbance value with the 0th test tube mixture as the reference. Plot the standard curve with ascorbic acid micrograms as the horizontal coordinate and the absorbance value as the vertical coordinate, and obtain the linear regression equation.

[0130] 2. Extraction

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

[0132] 3. Determination

[0133] Take 1.0 mL sample extract in test tube, add 1.0 ml 5% TCA solution, and then add other ingredients according to the same method of making standard curve, carry out reaction and determination. Record the absorbance value of reaction system at wavelength 534 nm. Repeat three times.

[0134] 4. Experimental results and calculation

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

[0136] Ascorbic acid content mg / 100g FW = [(VxC) / (Vs x W x 1000)] x 100

[0137] In the formula: C is the micrograms of ascorbic acid obtained from the standard curve, μg;

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

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

[0140] W is the sample weight, g.

[0141] II. Determination of weight loss rate:

[0142] Weigh the initial weight of the sample with an electronic balance, then weigh the weight every certain time, and calculate the weight loss rate according to the following formula:

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

[0144] In the formula: m1 is the initial mass, g;

[0145] m2 is the mass on the day of determination, g.

[0146] III. Determination of soluble solids

[0147] Randomly select 3-4 Dalian cherry fruits from each treatment group, peel and core to take the pulp, and squeeze the juice. Centrifuge at 8000 r / min for 10 min, and take the supernatant for standby. Use sugar meter PAL-108 to determine the soluble solids content.

[0148] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A method for micro-environmental air conditioning, humidification, cooling and preservation of cherries, characterized in that, It comprises the following steps: (1) preparing alkaline electrolytic water with pH 8.5-9.0, and then acidifying to pH 4.5-5.5 to obtain nano-acidic bubble water; Wash the cherries with nano-acidic bubble water and dry the surface moisture for standby; (2) placing the cherries in step (1) in a sterilization processor, and sterilizing the cherries after the positive ion generator processes the air and sends it to the sterilization processor; (3) soaking the cherries in step (2) in a sodium alginate coating solution for a period of time, and then air-drying; (4) heat-sealing the composite degradable modified atmosphere packaging film into a bag, and sealing the cherries in step (3) in the composite degradable modified atmosphere packaging bag, and storing it in a constant temperature and humidity environment; The composite degradable modified atmosphere packaging film is prepared by the following method: S1, preparation of copolyester PBTF: mixing furan dimethylate, catalyst, antioxidant and 1,4-butanediol, and heating to obtain a prepolymer polybutylene glycol 2,5-furandicarboxylate; then adding catalyst and polytetramethylene ether glycol to the system and continuing to heat, reducing pressure and increasing temperature, and ending the reaction when the climbing rod effect appears, purifying to obtain copolyester PBTF; S2, preparation of composite degradable modified atmosphere packaging film: uniformly mixing copolyester PBTF, polybutylene glycol adipate-terephthalate and solvent to obtain a casting solution, pouring the film, and drying to obtain the composite degradable modified atmosphere packaging film.

2. The cherry micro-environmental air conditioning and humidifying cooling preservation method according to claim 1, characterized in that, The cherries in step (1) are Dalian cherries; The alkaline electrolytic water with pH 8.5-9.0 in step (1) is obtained by electrolyzing 1-4 wt% NaCl solution; The acidification in step (1) is carried out with citric acid to pH 4.5-5.5; The positive ion generator processes the air for 15-20 min in step (2); and the sterilization treatment of Dalian cherries is carried out for 5-10 min; The concentration of the sodium alginate coating solution in step (3) is 1.5-4 wt%, which is obtained by heating sodium alginate and water to complete dissolution and defoaming; The soaking time in step (3) is 1-5 min; The constant temperature and humidity environment in step (4) refers to an environment with temperature of 25±3℃ and humidity of 90-95%; The constant temperature and humidity environment in step (4) is obtained by the following method: opening holes on each side of the foam insulation box, and attaching microporous membranes on the holes; adding bacterial nanocellulose hydrogel as a heat preservation layer in the foam insulation box; and placing dry ice between the heat preservation layer and the wall of the foam insulation box.

3. The cherry micro-environment air conditioning and humidification cooling preservation method according to claim 2, characterized in that, The foam insulation box has 4-8 holes with a diameter of 5-7 cm on each of the six sides; and the microporous membrane has a pore size of 1-10 nm.

4. The cherry micro-environment air conditioning and humidification cooling preservation method according to claim 1, characterized in that, The composite degradable modified atmosphere packaging film is prepared by the following method: S1, Preparation of copolyester PBTF: after furan dimethylate, catalyst, antioxidant and 1,4-butanediol were mixed, the mixture was heated at 90-95℃ until the liquid was uniform and transparent, then the temperature was increased to 180-185℃, and the reaction was continued until the temperature at the top of the reaction container was over 100℃, and the methanol distillate reached 93% of the theoretical value, to obtain the prepolymer polybutylene 2,5-furandicarboxylate; the temperature of the system was increased to 210-215℃, and catalyst and polytetramethylene ether glycol were added and reacted for 15-20 min, then the pressure of the system was reduced to 80-100 Pa, and the temperature was continuously increased at a rate of 10-15℃ / h, and the reaction was ended when the climbing rod effect appeared, and the copolyester PBTF was obtained after purification; the reaction was carried out in an inert gas atmosphere; S2, Preparation of composite degradable modified atmosphere packaging film: copolyester PBTF, polybutylene adipate terephthalate and solvent were mixed to obtain casting solution, and the film was poured and dried to obtain the composite degradable modified atmosphere packaging film.

5. The cherry micro-environmental air conditioning and humidifying cooling preservation method according to claim 4, characterized in that, In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to 1,4-butanediol was (1-5):(8-10); In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to antioxidant was (995-1000):(1-5); In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to catalyst was (995-1000):(3-10); In S1, the molar ratio of the added catalyst to furan dimethylate was (1.5-2.0):(995-1000), and the mass ratio of polytetramethylene ether glycol to the prepolymer polybutylene 2,5-furandicarboxylate was (11-15):(20-25) when the temperature of the system was increased to 210-215℃. The antioxidant in S1 is at least one of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl ester. The catalyst in S1 is at least one of butyl titanate and trimethyl phosphate. The molecular weight of the polytetramethylene ether glycol in S1 is 500-1500.

6. The cherry micro-environment conditioning, humidifying and cooling preservation method according to claim 1, characterized in that, The copolyester PBTF in S2 accounts for 1-5% of the total mass of copolyester PBTF and polybutylene adipate terephthalate. The molecular weight of the polybutylene adipate terephthalate in S2 is 10000-15000. The concentration of the casting solution in S2 is 15-20 wt%.

7. The cherry micro-environment air conditioning and humidification cooling preservation method according to claim 4, characterized in that, In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to 1,4-butanediol was 5:

9. In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to antioxidant was 1000:

1. In the preparation process of the prepolymer polybutylene 2,5-furandicarboxylate in S1, the molar ratio of furan dimethylate to catalyst was 1000:

3. The molar ratio of the catalyst to dimethyl furandicarboxylate is 1.5:1000, and the mass ratio of polytetramethylene ether glycol to the prepolymer polybutylene 2,5-furandicarboxylate is 11:20 when the system temperature is increased to 210-215 DEG C in S1; The inert gas is at least one of argon, helium and nitrogen in S1; The copolyester PBTF accounts for 2-5% of the total mass of the copolyester PBTF and polybutylene terephthalate-adipate in S2.

Images