Xinmei low-voltage electrostatic field synergistic special fresh-keeping packaging storage method and application

Abstract

The present invention belongs to the field of fruit and vegetable preservation technology and discloses a method for storing new plums in a low-voltage electrostatic field-coordinated special fresh-keeping packaging, comprising the following steps: (1) special packaging for non-damage harvesting: selecting new plum fruits that have reached physiological maturity, have intact fruit powder, and have green stems, and non-damage harvesting with gloves, and placing them in a mesh plastic basket with a special fresh-keeping packaging on the inner surface; (2) pre-cooling and fumigation before storage; and (3) LVEF cold storage. The method of the present invention integrates a new plum post-harvest storage and preservation technology system of "non-damage harvesting under the tree → direct packaging → tying and transportation → forklift storage → pre-cooling and fumigation → storage under an electric field." The entire process does not involve secondary grading, secondary handling, or secondary basket dumping, thereby minimizing mechanical damage, protecting the surface fruit powder intact, maintaining the green color and firmness of the stems, and extending the storage period of new plums to 3 months, with a water loss rate of less than 5% and a good fruit rate of more than 95%.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and in particular to a low-voltage electrostatic field coordinated special fresh-keeping packaging storage method for new plums and its application. Background Art

[0002] New plums have a strong aroma and a crisp taste, and are rich in vitamins, minerals, dietary fiber and antioxidant active ingredients.

[0003] The harvest season for new plums is concentrated in the hot season of August and September. As a result, plums are characterized by a high respiratory rate, resulting in a high metabolic rate after harvest. At room temperature, they begin to soften and rot after about six days. The powder on the skin of new plums is a naturally occurring sugar alcohol formed during growth. Its hydrophobic properties reduce postharvest water loss and act as a natural barrier against disease. Intact powder and a deep green stalk are hallmarks of new plum freshness. Harvesting, grading, and packaging, along with other commercial processes, are prone to mechanical damage, resulting in a loss of powder, browning or even blackening of the stalk, and eventual falloff. Water evaporation and material consumption accelerate at the pedicle abscission layer, leading to severe water loss and shrinkage. Microorganisms can enter through natural pores, exacerbating browning and rot in the flesh.

[0004] Current literature and patent disclosures on methods for storing and preserving new plums involve 1-MCP treatment alone or in combination with fungicides, ice-temperature storage, controlled atmosphere preservation, chemical coating, etc. The storage period basically remains at 1-2 months, which is still far from the 3 months or more required by enterprises and the market (that is, if stored until around New Year's Day, the price can double).

[0005] Through searching, we found the following patent publications related to the patent application of this invention:

[0006] 1. A method for storing prunes in an ice-controlled atmosphere (CN 114403207 A) employs an ice temperature of -5°C to 0°C (fluctuation ≤ 0.5°C) combined with an O2 concentration of 1-19% and a CO2 concentration of 0-5% to preserve fresh prunes. This method utilizes a stepwise cooling system for entry and a stepwise heating system for exit, achieving a storage period of 20 to 50 days. However, this method has the following issues: the freezing point of prunes is approximately -2.2°C, and ice storage at -5°C can cause freeze or chill damage; the prunes are fully ripened and senescent upon exit, making re-injection of ethylene gas for ripening ineffective; and the storage period does not exceed two months.

[0007] 2. A method and application for the storage and preservation of prunes (CN 112868750 A) involves pre-harvest spraying with a nutrient preservative, transporting the prunes into portable atmosphere-controlled containers, and subjecting them to physiological regulation with 1-MCP, along with physical preservation during storage. This method preserves surface frost, maintains fruit firmness, and reduces decay. However, the patented method has a 40-day storage period for prunes, and the high cost and limited capacity of the atmosphere-controlled containers (2.0 to 2.5 kg) make it unsuitable for large-scale industrial application.

[0008] 3. A cold chain logistics storage and preservation method for prunes and its application (CN 114831173 A). After harvesting at the production site, methyl jasmonate is treated with 1-MCP. After cold chain transportation in ice boxes, the prunes are stored in a cold storage at 3-5°C and wrapped with natamycin. The prunes can be stored for 35 days, effectively maintaining flesh firmness and reducing rot. However, the prunes in this patent are exposed to multiple preservatives, including MeJA, 1-MCP, and natamycin, simultaneously, posing a potential risk of residual residues. Furthermore, the prunes are fumigated, air-dried, and then packed into portable boxes for transportation, which involves unloading the boxes, which is very detrimental to the preservation of fruit powder and stems.

[0009] Based on the above industry status and needs, it is urgent to develop green physical preservation technology for new plums after harvest. On the premise of ensuring the commercial properties of the fruit such as color, aroma, taste and texture, the storage period can be extended to 3 months to achieve loss reduction and value-added in the new plum industry. Summary of the Invention

[0010] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method and application for storing new plums in a special fresh-keeping packaging using a low-voltage electrostatic field.

[0011] The technical solution adopted by the present invention to solve its technical problem is:

[0012] A method for storing new plums in a special fresh-keeping packaging using a low-voltage electrostatic field, comprising the following steps:

[0013] (1) Special packaging for non-injury harvesting: Select new plum fruits that have reached physiological maturity, have intact fruit powder, and have green stems. Wear gloves to harvest them without injury and put them into a mesh plastic basket with a special fresh-keeping packaging on the inner surface;

[0014] The special fresh-keeping packaging includes microporous aluminum foil, a degradable fresh-keeping bag, a shockproof cushion and a special fresh-keeping pad. The microporous aluminum foil is directly wrapped around the new plum fruit, and the degradable fresh-keeping bag is wrapped around the microporous aluminum foil. A shockproof cushion is set between the bottom of the outer surface of the degradable fresh-keeping bag and the bottom of the mesh plastic basket, and a special fresh-keeping pad is set between the bottom of the outer surface of the microporous aluminum foil and the degradable fresh-keeping bag.

[0015] (2) Pre-cooling and fumigation before storage: The harvested and packaged new plums are tightly packed for transportation and stored in time within 2 to 12 hours. The bags are opened after storage. The storage temperature is 0±0.5℃. Pre-cooling and 1-MCP fumigation are carried out simultaneously in an airtight environment. The treatment time is 12 to 14 hours, and the 1-MCP concentration is 1 to 1.5 μg / m 3 The temperature of the fruit core drops to 0℃, and the bag is tied tightly after the end. The timeliness of 1-MCP fumigation is within 12 hours after the fruit is harvested.

[0016] (3) LVEF cold storage: After pre-cooling and fumigation, the new plums enter the storage stage. The storage temperature is 0±0.5℃ and the humidity is 90%~95%. A low-voltage electrostatic field is used for storage. The output voltage of the low-voltage electrostatic field is 2000~4000V, the output current is 3~5mA, the electrode plate size is 46cm×51cm, and the distance between the upper electrode plate and the lower electrode plate is 40cm.

[0017] Furthermore, the thickness of the degradable fresh-keeping bag is 0.038±0.005 mm, the air permeability is 0.2-0.5 μm, and the antibacterial rates against Escherichia coli and Staphylococcus aureus reach 83% and 92% respectively.

[0018] Furthermore, the pore density of the microporous aluminum foil is 200 to 499 per cm 2 The pore size is 30-50 μm, and water molecules and 1-MCP can pass through normally.

[0019] Furthermore, the special fresh-keeping pad is a composite nanofiber pad with directional water conduction and antibacterial functions, including a water-conducting and breathable layer, a water-absorbing and controlled-release layer, and a waterproof barrier layer. The specific preparation method is as follows:

[0020] (1) Preparation of a water-conducting and breathable layer: First, cellulose acetate is dissolved in an acetic acid / water mixed solvent, wherein the mass concentration of cellulose acetate is 10% to 17%. The acetic acid / water mixed solvent is obtained by mixing acetic acid and water, and the volume ratio of acetic acid to water is 70:30 to 75:25. The mixture is magnetically stirred at room temperature until it is fully dissolved. Then, the above-mentioned mixture is electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The obtained spun fiber membrane is dried at 60 to 80° C. to obtain a CA water-conducting and breathable layer having weak hydrophilicity.

[0021] (2) Preparation of a water-absorbing controlled-release layer: First, polyvinyl alcohol was added to ultrapure water at a mass concentration of 7% to 12%, and the polyvinyl alcohol was heated to 85 to 100°C to completely dissolve to obtain a PVA aqueous solution; then, acetic acid and chitosan were added to the PVA aqueous solution in sequence, with the mass concentration of acetic acid being 3% to 12% and the mass concentration of chitosan being 1% to 3%, to obtain a composite fluid; finally, the composite fluid was subjected to electrospinning at a feed rate of 0.05 to 0.24 mL / h, an applied voltage of 15 to 23 kV, a spinning receiving distance of 8 to 12 cm, and a thermal crosslinking temperature of 180 to 230°C to obtain a CS / PVA-AA water-absorbing controlled-release layer having strong hydrophilicity;

[0022] (3) Preparation of waterproof barrier layer: First, polyurethane is dissolved in a tetrahydrofuran / N,N-dimethylformamide mixed solvent, the mass concentration of polyurethane is 12% to 17%, the tetrahydrofuran / N,N-dimethylformamide mixed solvent is obtained by mixing tetrahydrofuran and N,N-dimethylformamide, the volume ratio of tetrahydrofuran to N,N-dimethylformamide is 1:1 to 5:1, and magnetic stirring is performed at room temperature until it is fully dissolved; then the above-mentioned mixed solution is electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The obtained spun fiber membrane is dried at 60 to 80°C to obtain a hydrophobic PU waterproof barrier layer;

[0023] (4) Preparation of special fresh-keeping mat: The prepared water-conducting and breathable layer, water-absorbing and controlled-release layer and waterproof barrier layer are sprayed and fixed in sequence from top to bottom by a glue spraying machine to form a CA / CS / PVA-AA / PU special fresh-keeping mat.

[0024] Furthermore, an LVEF device is used for low-voltage electrostatic field storage, wherein the LVEF device includes a device body, a voltage converter, an upper electrode plate, a lower electrode plate, and a plastic basket placement cavity. The upper electrode plate, the lower electrode plate, and the plastic basket placement cavity are connected on the device body. The upper electrode plate is arranged above the lower electrode plate in parallel and at intervals. The upper electrode plate and the lower electrode plate are both connected to the power supply through the voltage converter. The lower electrode plate is also grounded to the ground. A plastic basket placement cavity is arranged on the device body between the upper electrode plate and the lower electrode plate. A mesh plastic basket for holding new plum fruits can be detachably and movably arranged in the plastic basket placement cavity.

[0025] Application of the above method in the preservation and / or storage of new plums.

[0026] The advantages and positive effects achieved by the present invention are:

[0027] 1. The present invention addresses the physiological characteristics of new plums' respiratory transitions. The innermost layer of packaging, a microporous aluminum foil, provides strong barrier properties, maximizing light isolation and retaining moisture. The outer layer, a degradable fresh-keeping bag, further provides moisture retention and breathability, spontaneously regulating the respiration of the new plums. A specialized fresh-keeping mat between the two layers of packaging not only directs moisture generated by fruit respiration or ambient temperature fluctuations through a weakly hydrophilic layer under capillary action into the middle, water-absorbing, controlled-release layer, but also blocks moisture through the bottom, hydrophobic layer. This integrated, specialized packaging system coordinates to maintain the integrity of the new plum powder and the freshness of the stem and fruit, addressing the problem of post-harvest wilting of new plums due to water loss.

[0028] 2. The method of the present invention uses the external electric field environment created by the LVEF cold storage to change the inherent electric field inside the new plum fruit, inhibit metabolism, regulate physiological enzyme activity, affect the electron transfer of the respiratory chain, etc. At the same time, the negative ions generated have the effect of decomposing ethylene. Combined with the competition of 1-MCP fumigation within the precise time range after harvest for ethylene receptors, the respiratory rate is jointly slowed down, material consumption is reduced, and the problem of softening and aging of new plums after harvest is solved.

[0029] 3. In the method of the present invention, the external storage environment affects the cell membrane permeability of microorganisms within a certain range through the electric field and ionization of the LVEF cold storage, and the ions interact with the substances in the membrane to block the physiological and biochemical reactions, thereby killing the microorganisms; the internal storage environment is achieved through the addition of chitosan in the water-absorbing controlled release layer of the special fresh-keeping pad, and its positively charged NH 3+ The groups undergo typical ionic electrostatic adsorption with the negatively charged components in the microorganisms, resulting in the leakage of microbial cell components and inducing cell death. In addition, the intercalation antibacterial effect of the degradable fresh-keeping bag and the antibacterial effect of the biological interaction between the aluminum foil material and LVEF jointly create an antibacterial environment of "external prevention and internal control" to solve the problem of mildew and rot after the new plums are picked.

[0030] 4. The method of the present invention integrates a new plum post-harvest storage and preservation technology system of "harmless harvesting under the tree → direct packaging → tying and transportation → forklift storage → pre-cooling and fumigation → storage under an electric field". The whole process does not involve secondary grading, secondary transportation, secondary basket dumping and other operations, which minimizes mechanical damage to the greatest extent, protects the surface fruit powder intact, maintains the green color and hardness of the fruit stalk, and extends the storage period of new plums to 3 months. The water loss rate is less than 5%, and the good fruit rate is greater than 95%.

[0031] 5. Compared to traditional preservation technologies, low-voltage electrostatic field (LVEF) is a non-contact, green, non-destructive, safe, and effective non-thermal physical method. It can create an ion-driven environment through spatial discharge, affecting the charge distribution and water activity within the fruit within a certain distance, further altering physiological enzyme activity and microbial growth. Specialized packaging that combines the physiological characteristics of new plums with the preservation needs of fresh plums is urgently needed. It should not only retain water and regulate respiration, but also provide sustained-release antibacterial properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the packaging of fresh plums during the preservation process of the present invention;

[0033] Figure 2 The diagram of the low-voltage electrostatic field treatment of Xinmei in the present invention; wherein, A: a photo of the actual object treated by the experiment; B: a schematic diagram of the structural connection of the LVEF device;

[0034] Figure 3 These are sensory photos of the new plums in the present invention after different packaging treatments and storage for 90 days under LVEF;

[0035] Figure 4 These are sensory photos of new plums stored for 90 days in different packaging and electric field treatment according to the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the following examples. The following examples are descriptive rather than restrictive, and the scope of protection of the present invention cannot be limited by the following examples.

[0037] The various experimental operations involved in the specific embodiments are all routine techniques in the field. For parts not specifically annotated in this document, ordinary technicians in this field can refer to various commonly used reference books, scientific literature or related instructions, manuals, etc. before the filing date of this invention to implement them.

[0038] A method for storing new plums in a special fresh-keeping packaging using a low-voltage electrostatic field, comprising the following steps:

[0039] 1. Special packaging for non-injury harvesting: Select new plum fruits that have reached physiological maturity, have intact fruit powder, and have green stems. Wear gloves to harvest them without injury and put them into a mesh plastic basket with a special fresh-keeping packaging on the inner surface.

[0040] like Figure 1As shown, the special fresh-keeping package includes a microporous aluminum foil 3, a degradable fresh-keeping bag 2, a shockproof cushion 6 and a special fresh-keeping pad 5. The microporous aluminum foil is directly wrapped around the new plum fruit 4, and the degradable fresh-keeping bag is wrapped around the microporous aluminum foil. A shockproof cushion is set between the bottom of the outer surface of the degradable fresh-keeping bag and the bottom of the mesh plastic basket, and a special fresh-keeping pad is set between the bottom of the outer surface of the microporous aluminum foil and the degradable fresh-keeping bag.

[0041] Specifically, it can be understood that the fresh-keeping packaging is divided into two layers. The inner layer is microporous aluminum foil that directly wraps the new plum fruit, and the outer layer is a degradable fresh-keeping bag. There is a commercially available shock-proof cushioning pad between the outermost plastic basket bottom and the fresh-keeping packaging, and a special fresh-keeping pad is placed between the microporous aluminum foil and the degradable fresh-keeping bag.

[0042] Among them, the design and preparation method of the above-mentioned degradable fresh-keeping bag can be found in the inventor's authorized invention patent ZL202111600215.3. The thickness of the fresh-keeping bag is 0.038±0.005mm, the air permeability is 0.2~0.5μm, and the antibacterial rates against Escherichia coli and Staphylococcus aureus reach 83% and 92% respectively.

[0043] The pore density of the microporous aluminum foil is 200 to 499 pores / cm 2 The pore size is 30-50 μm, and water molecules and 1-MCP can pass through normally.

[0044] The special fresh-keeping mat is a composite nanofiber mat with directional water conduction and antibacterial functions, including a water-conducting and breathable layer, a water-absorbing and controlled-release layer, and a waterproof barrier layer. The specific preparation method is as follows:

[0045] (1) Preparation of a water-conducting and breathable layer: First, cellulose acetate (CA) is dissolved in an acetic acid / water mixed solvent with a CA mass concentration of 10% to 17%. The acetic acid / water mixed solvent is obtained by mixing acetic acid and water, and the volume ratio of acetic acid to water is 70:30 to 75:25. The mixture is magnetically stirred at room temperature until it is fully dissolved. The mixture is then electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The resulting spun fiber membrane is dried at 60 to 80° C. to obtain a CA water-conducting and breathable layer having weak hydrophilicity.

[0046] (2) Preparation of a water-absorbing controlled-release layer: First, polyvinyl alcohol (PVA) was added to ultrapure water with a mass concentration of 7% to 12%, and the PVA aqueous solution was prepared after being completely dissolved by heating to 85 to 100°C; then, acetic acid (AA) and chitosan (CS) were added to the above-mentioned PVA aqueous solution in sequence, with the mass concentration of acetic acid being 3% to 12% and the mass concentration of chitosan being 1% to 3%, to prepare a composite fluid; finally, the above-mentioned composite fluid was subjected to electrospinning at a feed rate of 0.05 to 0.24 mL / h, an applied voltage of 15 to 23 kV, a spinning receiving distance of 8 to 12 cm, and a thermal crosslinking temperature of 180 to 230°C to obtain a CS / PVA-AA water-absorbing controlled-release layer with strong hydrophilicity;

[0047] (3) Preparation of waterproof barrier layer: First, polyurethane (PU) is dissolved in a tetrahydrofuran (THF) / N,N-dimethylformamide (DMF) mixed solvent, with a mass concentration of polyurethane of 12% to 17%. The tetrahydrofuran (THF) / N,N-dimethylformamide (DMF) mixed solvent is obtained by mixing tetrahydrofuran and N,N-dimethylformamide, and the volume ratio of tetrahydrofuran to N,N-dimethylformamide is 1:1 to 5:1. The mixture is magnetically stirred at room temperature until it is fully dissolved. Then, the above-mentioned mixture is electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The obtained spun fiber membrane is dried at 60 to 80 ° C to obtain a hydrophobic PU waterproof barrier layer.

[0048] (4) Preparation of special fresh-keeping mat: The prepared water-conducting and breathable layer, water-absorbing and controlled-release layer and waterproof barrier layer are sprayed and fixed in sequence from top to bottom by a glue sprayer to form a CA / CS / PVA-AA / PU special fresh-keeping mat; the special fresh-keeping mat can not only prevent condensation in the new plum packaging from affecting the fruit powder and then rotting through directional water conduction, but also lock in moisture through the hydrophobic barrier layer to prevent the fruit from losing water and wilting, and the fruit stalks from drying up and turning green, while ensuring the integrity of the fruit powder and the freshness of the fruit stalks.

[0049] 2. Pre-cooling and fumigation before storage: The harvested and packaged new plums should be tightly packed for transportation and stored in time within 2 to 12 hours. After storage, the bags should be opened (i.e., the microporous aluminum foil and biodegradable fresh-keeping bags should be opened). The storage temperature should be 0±0.5℃. Pre-cooling and 1-MCP fumigation should be carried out simultaneously in an airtight environment. The treatment time should be 12 to 14 hours, and the 1-MCP concentration should be 1 to 1.5μg / m 3 The temperature of the fruit core drops to 0°C, and the bag is tied tightly after the end. It should be noted that the timeliness of 1-MCP fumigation is within 12 hours after the fruit is harvested. If it exceeds 24 hours, the effect will be weak.

[0050] 3. LVEF cold storage: After pre-cooling and fumigation, the new plums enter the storage stage. The storage temperature is 0±0.5℃ and the humidity is 90%~95%. A low-voltage electrostatic field is used for storage. The output voltage of the low-voltage electrostatic field is 2000~4000V, the output current is 3~5mA, the electrode plate size is 46cm×51cm, and the distance between the upper and lower plates is 40cm.

[0051] Preferably, one can use Figure 2 The LVEF device shown in the figure includes a device body 11, a voltage converter 7, an upper electrode plate 9, a lower electrode plate 8 and a plastic basket placement cavity 10. The upper electrode plate, the lower electrode plate and the plastic basket placement cavity are connected on the device body. The upper electrode plate is arranged above the lower electrode plate in parallel and spaced apart. The upper electrode plate and the lower electrode plate are both connected to a power supply (not shown in the figure) through a voltage converter. The lower electrode plate is also grounded to the ground. A plastic basket placement cavity is arranged on the device body between the upper electrode plate and the lower electrode plate. A mesh plastic basket for holding new plum fruits can be detachably and movably arranged in the plastic basket placement cavity, which facilitates the LVEF device to perform low-voltage electrostatic field storage operations on the mesh plastic basket for holding new plum fruits.

[0052] The contents not described in detail in the following embodiments are the same as those in this section.

[0053] Specifically, the relevant preparation and detection are as follows:

[0054] Example 1

[0055] 1. Experimental treatment

[0056] New plum fruits that have reached physiological maturity, with intact fruit powder and green stems, were harvested from the new plum planting base in Jiashi County, Kashgar Prefecture, Xinjiang Uygur Autonomous Region. They were harvested without injury by wearing gloves, packed in different packages, and placed in mesh plastic baskets. They were stored for pre-cooling within 12 hours at a temperature of 0±0.5℃ and fumigated with 1-MCP in an airtight environment for 12 hours at a concentration of 1μg / m 3 , and the relevant indicators were counted after 90 days of storage.

[0057] Different packaging treatments are:

[0058] Package A: Net bag alone; Package B: Aluminum foil alone; Package C: Net bag + degradable fresh-keeping bag; Package D: Aluminum foil + degradable fresh-keeping bag; Package E: Aluminum foil + degradable fresh-keeping bag + the special fresh-keeping pad of the present invention.

[0059] 2. Experimental results

[0060] Table 1 Effect of different packaging on the quality of new plums after 90 days of storage

[0061] index Packaging A Packaging B Packaging C Packaging D Packaging E Water loss rate (%) 7.41 5.53 5.89 5.01 4.85 Decay rate (%) 32.7 12.5 13.1 7.6 6.8 <![CDATA[Fruit hardness (kg / cm 2 )]]> / 5.5 5.4 8.5 10.6

[0062] As shown in Table 1, new plum fruits packaged in net wraps alone experienced severe water loss and decay after 90 days of storage, with water loss and decay rates reaching 7.41% and 32.7%, respectively. The fruits softened completely, and their firmness became undetectable. Aluminum foil and biodegradable fresh-keeping bags, each offering varying degrees of barrier properties to water loss and microorganisms, mitigated water loss and maintained fruit firmness compared to Package A, while significantly reducing decay rates by 20.2% and 19.6%, respectively. Aluminum foil combined with biodegradable fresh-keeping bags further maintained humidity during storage, resulting in a water loss rate approaching 5%, further enhancing microbial barrier properties and disease resistance, with a decay rate of 7.6%. Package E, incorporating the specialized fresh-keeping packaging of the present invention, incorporates a custom-made fresh-keeping mat based on Package D, providing directional water conduction and moisture retention. This resulted in a water loss rate of only 4.85%, and combined with the broad-spectrum antibacterial properties of chitosan, reduced decay rates to 6.8%, effectively mitigating the problems of post-harvest wilting, mold, and decay in new plums. At the same time, it can also be seen that the aluminum foil, degradable fresh-keeping bag and special fresh-keeping pad used in the method of the present invention have a synergistic effect, which can synergistically promote the preservation effect of new plums.

[0063] Example 2

[0064] 1. Experimental treatment

[0065] New plum fruits that had reached physiological maturity, had intact fruit powder, and had green stems were harvested from a new plum planting base in Jiashi County, Kashgar Prefecture, Xinjiang Uygur Autonomous Region. They were harvested without injury by wearing gloves, packed into four different packages, and then placed in mesh plastic baskets. The bottoms of the baskets were padded with commercially available shock-proof cushioning pads and homemade special fresh-keeping pads. They were pre-cooled in storage within 12 hours at a temperature of 0±0.5℃ and fumigated with 1-MCP in an airtight environment for 12 hours at a concentration of 1μg / m 3 After fumigation, the LVEF device is turned on, with an output voltage of 3000V, an output current of 3mA, an electrode plate size of 46cm×51cm, and a distance of 40cm between the upper and lower plates. Figure 3 As shown:

[0066] Treatment A: Net cover alone + LVEF; Treatment B: Aluminum foil alone + LVEF; Treatment C: Net cover + degradable fresh-keeping bag + LVEF; Treatment D: Aluminum foil + degradable fresh-keeping bag + LVEF.

[0067] 2. Experimental results

[0068] Table 2 Effect of different packaging on the quality of new plums after 90 days of storage under LVEF

[0069] index Process A Treatment B Process C Processing D Water loss rate (%) 7.26 5.24 5.87 4.82 Decay rate (%) 11.8 9.1 10.4 4.6 <![CDATA[Fruit firmness (kg / cm 2 )]]> / 8.7 6.5 11.2 Soluble solids content (TSS, %) 21.2 22.4 21.5 23.4 Total acid content (%) 0.87 1.85 1.63 2.02

[0070] As shown in Table 2 and Figure 3As shown in Table 1, the sensory and quality changes of new plum fruits stored for 90 days under different packaging conditions under low-voltage electrostatic field are shown in Table 1 and Figure 3 The new plum fruits in treatment A, which were packaged in a single net, were seriously moldy, with a rot rate of 11.8%. The fruit stalks all turned green and dried up and partially fell off. The connection between the fruit stalks and the fruit shrank, and the overall water loss rate reached 7.26%. The fruits were all softened and the hardness was unmeasurable. In treatment B, the fruit stems of the fruit were packaged in aluminum foil alone, turning yellow-green but not falling off. The rot rate was 9.1%, the moisture retention was good, the water loss was only 5.24%, the fruit softened to a certain extent, and the TSS and total acid contents remained good. In treatment C, the fruit stems of the fruit were packaged in a degradable fresh-keeping bag, turning yellow-brown and part of the fruit stems fell off. The rot rate was 10.4%, the water loss rate was 5.87%, and the fruit softened to a greater extent than treatment B. Compared with treatment A, both groups delayed the softening and rot of the new plum fruit after harvest to a certain extent, and the effect of treatment B was better than treatment C. Treatment D is the special fresh-keeping packaging for new plums in the present invention. Combined with the electrostatic field treatment, it effectively maintains the integrity of the fruit powder and the fruit stem. The water loss rate is <5%, the good fruit rate is >95%, and the TSS and total acid contents remain at a high level, which has a significant fresh-keeping effect on new plums. At the same time, it can also be seen that the aluminum foil, degradable fresh-keeping bag and low-voltage electrostatic field used in the method of the present invention have a synergistic effect, which can synergistically promote the fresh-keeping effect of new plums.

[0071] Example 3

[0072] 1. Experimental treatment: New plum fruits that have reached physiological maturity, with intact fruit powder and green stems, were harvested from the new plum planting base in Jiashi County, Kashgar Prefecture, Xinjiang Uygur Autonomous Region. They were harvested without injury by wearing gloves, packed in different packages, and placed in mesh plastic baskets. They were stored for pre-cooling within 12 hours at a temperature of 0±0.5℃ and fumigated with 1-MCP in an airtight environment for 12 hours at a concentration of 1μg / m 3 , the mice were divided into groups and processed for LVEF, and the relevant indicators were counted after 90 days of storage.

[0073] The treatments are divided into the following categories: Treatment A: Net bag alone; Treatment B: Special fresh-keeping packaging of the present invention (i.e., aluminum foil + reducible bag + special fresh-keeping pad); Treatment C: Net bag alone + LVEF treatment; Treatment D: Special fresh-keeping packaging of the present invention + LVEF treatment.

[0074] 2. Experimental results

[0075] Table 3 Effects of different packaging and electric field treatment on the quality of new plums after 90 days of storage

[0076] index Process A Treatment B Process C Processing D Water loss rate (%) 7.41 4.85 7.26 4.82 Decay rate (%) 32.7 6.8 11.8 4.6 <![CDATA[Fruit firmness (kg / cm 2 )]]> / 10.6 / 11.2 Soluble solids content (TSS, %) 20.8 22.5 21.2 23.4 Total acid content (%) 0.56 1.64 0.87 2.02

[0077] As shown in Table 3 and Figure 4As shown, the results of net-wrapped packaging for new plums, as described in Example 1, showed severe water loss and decay after 90 days of storage, with water loss and decay rates reaching 7.41% and 32.7%, respectively. The fruits were completely softened and their firmness was unmeasurable. In contrast, after LVEF treatment, the electric field and ionization affected the permeability of microbial cell membranes and the leakage of cell contents, achieving an antibacterial effect and reducing the decay rate by 20.9%. The special fresh-keeping packaging of the present invention combines moisturizing, atmosphere control, and antibacterial properties. After 90 days of storage, the new plums had a water loss rate of 4.85% and a decay rate of 6.8%, while maintaining high levels of TSS and total acid content. The treatment group combining a low-voltage electrostatic field and special fresh-keeping packaging maximized the protection of the surface fruit powder, maintained the green color and firmness of the fruit stem, slowed the respiratory aging rate of the fruit, and created an antibacterial environment of "external protection and internal control." This extended the storage period of new plums to 3 months, while maintaining a water loss rate of less than 5% and a good fruit rate greater than 95%. At the same time, it can also be seen that the aluminum foil, degradable fresh-keeping bag, special fresh-keeping pad and low-voltage electrostatic field used in the method of the present invention have a synergistic effect, which can synergistically promote the preservation effect of new plums.

[0078] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for storing new plums in a low-voltage electrostatic field-coordinated special fresh-keeping packaging, characterized by: The steps include: (1) Special packaging for non-injury harvesting: Select new plum fruits that have reached physiological maturity, with intact fruit powder and green stems, harvest them without injury while wearing gloves, and put them into a mesh plastic basket with a special fresh-keeping packaging on the inner surface; The special fresh-keeping packaging includes microporous aluminum foil, a degradable fresh-keeping bag, a shockproof cushion and a special fresh-keeping pad. The microporous aluminum foil is directly wrapped around the new plum fruit, and the degradable fresh-keeping bag is wrapped around the microporous aluminum foil. A shockproof cushion is set between the bottom of the outer surface of the degradable fresh-keeping bag and the bottom of the mesh plastic basket, and a special fresh-keeping pad is set between the bottom of the outer surface of the microporous aluminum foil and the degradable fresh-keeping bag. (2) Pre-cooling and fumigation before storage: The harvested and packaged new plums are tightly packed for transportation and stored in time within 2 to 12 hours. The bags are opened after storage. The storage temperature is 0±0.5℃. Pre-cooling and 1-MCP fumigation are carried out simultaneously in an airtight environment. The treatment time is 12 to 14 hours, and the 1-MCP concentration is 1 to 1.5 μg / m 3 The temperature of the fruit core drops to 0℃, and the bag is tied tightly after the end. The timeliness of 1-MCP fumigation is within 12 hours after the fruit is harvested. (3) LVEF cold storage: After pre-cooling and fumigation, the new plums enter the storage stage. The storage temperature is 0±0.5℃ and the humidity is 90%~95%. A low-voltage electrostatic field is used for storage. The output voltage of the low-voltage electrostatic field is 2000~4000V, the output current is 3~5mA, the electrode plate size is 46cm×51cm, and the distance between the upper electrode plate and the lower electrode plate is 40cm.

2. The method for storing new plums in low-voltage electrostatic field-coordinated fresh-keeping packaging according to claim 1, characterized in that: The thickness of the degradable fresh-keeping bag is 0.038±0.005 mm, the air permeability diameter is 0.2-0.5 μm, and the antibacterial rates against Escherichia coli and Staphylococcus aureus reach 83% and 92% respectively.

3. The method for storing new plums in low-voltage electrostatic field-coordinated fresh-keeping packaging according to claim 1, characterized in that: The pore density of the microporous aluminum foil is 200 to 499 pores / cm 2 The pore size is 30-50 μm, and water molecules and 1-MCP can pass through normally.

4. The method for storing new plums in low-voltage electrostatic field-coordinated fresh-keeping packaging according to claim 1, characterized in that: The special fresh-keeping mat is a composite nanofiber mat with directional water conduction and antibacterial functions, including a water-conducting and breathable layer, a water-absorbing and controlled-release layer, and a waterproof barrier layer. The specific preparation method is as follows: (1) Preparation of a water-conducting and breathable layer: First, cellulose acetate is dissolved in an acetic acid / water mixed solvent, wherein the mass concentration of cellulose acetate is 10% to 17%. The acetic acid / water mixed solvent is obtained by mixing acetic acid and water, and the volume ratio of acetic acid to water is 70:30 to 75:

25. The mixture is magnetically stirred at room temperature until it is fully dissolved. Then, the above-mentioned mixture is electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The obtained spun fiber membrane is dried at 60 to 80° C. to obtain a CA water-conducting and breathable layer having weak hydrophilicity. (2) Preparation of a water-absorbing controlled-release layer: First, polyvinyl alcohol was added to ultrapure water at a mass concentration of 7% to 12%, and the polyvinyl alcohol was heated to 85 to 100°C to completely dissolve to obtain a PVA aqueous solution; then, acetic acid and chitosan were added to the PVA aqueous solution in sequence, with the mass concentration of acetic acid being 3% to 12% and the mass concentration of chitosan being 1% to 3%, to obtain a composite fluid; finally, the composite fluid was subjected to electrospinning at a feed rate of 0.05 to 0.24 mL / h, an applied voltage of 15 to 23 kV, a spinning receiving distance of 8 to 12 cm, and a thermal crosslinking temperature of 180 to 230°C to obtain a CS / PVA-AA water-absorbing controlled-release layer having strong hydrophilicity; (3) Preparation of waterproof barrier layer: First, polyurethane is dissolved in a tetrahydrofuran / N,N-dimethylformamide mixed solvent, the mass concentration of polyurethane is 12% to 17%, the tetrahydrofuran / N,N-dimethylformamide mixed solvent is obtained by mixing tetrahydrofuran and N,N-dimethylformamide, the volume ratio of tetrahydrofuran to N,N-dimethylformamide is 1:1 to 5:1, and magnetic stirring is performed at room temperature until it is fully dissolved; then the above-mentioned mixed solution is electrospun at a feed rate of 0.5 to 1 mL / h, an applied voltage of 15 to 23 kV, and a spinning receiving distance of 10 to 15 cm. The obtained spun fiber membrane is dried at 60 to 80°C to obtain a hydrophobic PU waterproof barrier layer; (4) Preparation of special fresh-keeping mat: The prepared water-conducting and breathable layer, water-absorbing and controlled-release layer and waterproof barrier layer are sprayed and fixed in sequence from top to bottom by a glue spraying machine to form a CA / CS / PVA-AA / PU special fresh-keeping mat.

5. The method for storing new plums in low-voltage electrostatic field-coordinated fresh-keeping packaging according to claim 1, characterized in that: An LVEF device is used for low-voltage electrostatic field storage. The LVEF device includes a device body, a voltage converter, an upper electrode plate, a lower electrode plate, and a plastic basket placement cavity. The upper electrode plate, the lower electrode plate, and the plastic basket placement cavity are connected on the device body. The upper electrode plate is arranged above the lower electrode plate in parallel and at intervals. The upper electrode plate and the lower electrode plate are both connected to a power supply through the voltage converter. The lower electrode plate is also grounded to the ground. A plastic basket placement cavity is provided on the device body between the upper electrode plate and the lower electrode plate. A mesh plastic basket for holding new plum fruits can be detachably and movably arranged in the plastic basket placement cavity.

6. Use of the method according to any one of claims 1 to 5 in the preservation and / or storage of new plums.

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