A method for preserving whole lotus roots with skin and its application

Abstract

This invention provides a method for preserving whole lotus roots with skin and its application. The method includes the following steps: selecting freshly harvested, uniformly sized, whole lotus roots with skin, free from mechanical damage, pests, and diseases; washing the surface of the selected whole lotus roots with skin with tap water to remove the soil, cutting off the root head and roots, and retaining the intact nodes; using a sterile fine needle with a diameter of 0.5-0.8 mm to pierce the nodes of the whole lotus root with skin to a depth of 4-6 mm, evenly piercing 4-6 holes in each node; completely immersing the lotus root in a nano-emulsion; vacuuming at 4-10℃ to a vacuum degree of 0.08-0.1 MPa and maintaining this vacuum for 10-30 minutes, then continuing to soak at normal pressure for 15-25 minutes; removing the lotus root and air-drying at 4-20℃ for 30-60 minutes; placing the treated lotus root in a food-grade micro-permeable vacuum packaging bag, vacuuming and sealing it; and storing the vacuum-packed lotus root at 4±1℃ and a relative humidity of 90±5%. The nanoemulsion and micro-permeable vacuum packaging bag of the present invention form a synergistic system, which significantly improves the preservation effect of lotus root.

Description

Technical Field

[0001] This invention belongs to the field of agricultural product preservation and storage technology, specifically relating to a method for preserving whole lotus roots with skin and its application. Background Technology

[0002] Lotus root is a unique aquatic vegetable in my country, widely cultivated in provinces such as Hubei, Hunan, Jiangsu, and Anhui. Rich in starch, dietary fiber, vitamin C, and other nutrients, lotus root is crisp, sweet, and delicious, making it a popular choice among consumers. However, due to its thin skin and tender flesh, lotus root is prone to dehydration, loss of crispness, browning, and rotting after harvest due to its own physiological metabolism and microbial growth, resulting in a very limited shelf life and severely restricting its sales radius. In recent years, research on lotus root preservation technology has mainly focused on peeled and cut fresh-cut lotus root, including various techniques such as chemical preservation, physical preservation, and biological preservation. Chemical preservation techniques often use substances such as citric acid, ascorbic acid, chitosan, and tea polyphenols to soak or coat fresh-cut lotus root, and combined with low temperatures, can extend the shelf life to 8-12 days. However, single preservatives often have the problem of large dosages with limited effectiveness. Furthermore, chemical preservation carries the risk of improper use and a loss of consumer trust. Physical preservation technologies include low temperature, heat treatment, modified atmosphere packaging, ultrasound, irradiation, ultra-high pressure, and pulsed electric field techniques. Studies have shown that 20% CO2 modified atmosphere packaging is effective in delaying browning of fresh-cut lotus root, but its storage period is only about 6 days. Vacuum packaging has a good effect on delaying the deterioration of the quality of fresh-cut lotus root, and its storage period can be extended to about 35 days. Biological preservation technologies utilize the metabolic products of microorganisms, such as nisin, to preserve fresh-cut lotus root and can inhibit the growth and reproduction of some spoilage bacteria. However, the preservation effect of a single biological preservative is limited and cannot meet the preservation requirements for a longer shelf life.

[0003] While the aforementioned technologies have extended the shelf life of fresh-cut lotus root to some extent, their direct application to whole lotus roots with the skin on faces the following technical bottlenecks: Technological mismatch and the current situation of "emphasizing cutting while neglecting whole lotus roots": Existing research mostly focuses on peeled fresh-cut lotus roots. Fresh-cut lotus root slices, due to mechanical damage, primarily need to address the problem of enzymatic browning. However, whole lotus roots have intact skin, and their deterioration mainly stems from the growth of microorganisms on the skin, internal respiration and metabolism, and water transpiration. Directly applying color-protecting technologies designed for cut surfaces to whole lotus roots is not only ineffective but also easily leads to waste of chemicals or the risk of residue. The "scissors difference" dilemma in storage period: As consumers increasingly prefer naturally prepared foods, the market demand for whole lotus roots with the skin on is growing year by year, with the market generally requiring a shelf life of over 30 days. However, current mainstream fresh-cut lotus root slice preservation technologies can only maintain shelf life for 8-12 days, while traditional whole lotus roots with mud on or simply refrigerated can only be preserved for 10-15 days in early autumn, far from meeting the needs of supermarket logistics, off-season sales, and export sales. The commercialization of highly effective preservatives is hampered: Although research has reported that treatment with ε-polylysine and 2,3-butanedione can extend the storage period of whole lotus roots to 40-55 days, showing great potential, these treatment methods are currently mostly in the laboratory stage. They cannot be directly used for commercial production for the time being due to high costs, regulatory applicability, or the technical difficulties of large-scale application.

[0004] Therefore, given the high cost of existing biological preservation, the risk of residue from chemical preservation, and the poor effectiveness of physical preservation, developing a green, safe, and specifically applicable preservation method for whole lotus roots with skin that can achieve a shelf life of more than 30 days has become a core technical challenge that the lotus root industry urgently needs to solve. Summary of the Invention

[0005] This invention provides a method for preserving whole lotus roots with skin and its application. A nanoemulsion and a food-grade micro-permeable vacuum packaging bag form a synergistic preservation system. The nanoemulsion responds to pH changes on the surface and inside of the lotus root, inhibiting the quality changes of the lotus root in stages. The micro-permeable vacuum packaging bag isolates external pollution and provides a micro-aerobic environment suitable for the survival of Lactobacillus plantarum, significantly improving the overall preservation effect.

[0006] The technical solution adopted by the present invention to achieve the above objectives is: a method for preserving whole lotus roots with skin, comprising the following steps: Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. Using a sterile fine needle with a diameter of 0.5-0.8 mm, pierce the nodes of the whole lotus root with skin into a depth of 4-6 mm, and evenly pierce 4-6 holes in each node. Completely immerse the lotus root in the nano-emulsion, and vacuum it at 4-10℃ to a vacuum degree of 0.08-0.1 MPa for 10-30 minutes. Then continue to soak it at normal pressure for 15-25 minutes. Remove the lotus root and air dry it at 4-20℃ for 30-60 minutes. Place the processed lotus root into a food-grade, slightly breathable vacuum packaging bag, vacuum it, and seal it. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity.

[0007] Preferably, the mass ratio of lotus root and nanoemulsion in step (3) is 1:3-5.

[0008] Preferably, the preparation steps of the nanoemulsion in step (3) are as follows: S1: Dissolve chitosan in a 1% (v / v) glacial acetic acid solution and stir until completely dissolved to prepare a 0.3% (w / w) chitosan solution; add lotus root polyphenol extract to sterile water to prepare a 0.2-0.5% (w / w) lotus root polyphenol extract solution; mix the chitosan solution and lotus root polyphenol extract solution thoroughly, and slowly add a 0.4% (w / w) sodium tripolyphosphate solution at a dropping rate of 1-2 mL / min while stirring at 300-500 rpm, continue stirring for 30-60 min, and adjust the pH of the system to 6.5-7.0 to obtain a chitosan-lotus root polyphenol nanoparticle suspension; S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 8 -1×10 10CFU / mL was used to obtain a bacterial suspension; the bacterial suspension was mixed with a 5-10% gelatin solution preheated to 40℃ at a volume ratio of 1:(2-4), and the pH of the system was adjusted to 6.2-6.8; at 4℃, the mixture was slowly and uniformly added dropwise to pre-cooled sterile vegetable oil, wherein the volume of sterile vegetable oil was 3-6 times that of the mixture. After the addition was completed, the mixture was allowed to stand and solidify at 4℃ for 10-15 min, and then stirred at 350-500 rpm for 15-25 minutes. After 1 minute, gelatin microspheres are formed. Most of the upper vegetable oil is separated and removed. Transglutaminase is added, and the mixture is cross-linked at 30-35℃ for 1.5-2 hours. The microgel is collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4℃ and containing 0.05-0.1% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel is resuspended in sterile water to a mass fraction of 10-15%. S3: Add liquid soybean lecithin to soybean oil and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:2-4 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at a high-speed shearing machine speed of 10000-12000 rpm and continue shearing for 5-10 min to obtain a crude emulsion; homogenize the crude emulsion through a high-pressure homogenizer at a pressure of 60-100 MPa 2-4 times, and after homogenization, rapidly cool to below 25℃, slowly add the microgel suspension at a speed of 200-300 rpm, continue stirring for 5-10 min, and adjust the pH of the system to 6.5-7.0 to obtain the nanoemulsion.

[0009] Preferably, the mass ratio of chitosan solution, lotus root polyphenol extract solution and sodium tripolyphosphate solution in S1 is 1 : (0.5-1.5) : (0.2-0.4).

[0010] Preferably, the amount of transglutaminase added in S2 is 1-2% of the total mass of the dried gelatin.

[0011] Preferably, the vegetable oil in S2 includes soybean oil, corn oil, sunflower seed oil, and peanut oil.

[0012] Preferably, the volume ratio of liquid soybean lecithin to soybean oil in S3 is 1:20-50.

[0013] Preferably, in S3, V 油相 V 初始水相 V 微凝胶悬液 =1 : (6-10) : (0.8-1.5).

[0014] Preferably, the preparation method of the food-grade micro-permeable vacuum packaging bag in step (4) is as follows: Fresh lotus root residue was washed, drained, dried at 70℃ to constant weight, and pulverized through an 80-mesh sieve. A 1.0 mol / L NaOH solution and a 0.5 mol / L Na₂SO₃ solution were mixed at a volume ratio of 1:2 to obtain a composite alkali solution. The lotus root residue powder was mixed with the composite alkali solution at a mass-volume ratio of 1 g:10 mL. After stirring in a water bath at 75℃ for 3 hours, the mixture was filtered. The solid was repeatedly washed with deionized water until neutral. The solid was hydrolyzed with 5% hydrochloric acid at 70℃ for 80 minutes, with a solid-to-hydrochloric acid mass-volume ratio of 1 g:15 mL. After filtration, the solid was washed with deionized water until neutral. The solid was dried at 60℃ and ultra-finely pulverized to obtain lotus root residue microcrystalline cellulose O-MCC powder. Based on 100 parts by weight of food-grade low-density polyethylene resin, 10 parts of O-MCC powder dried at 65℃ for 6 hours, 3 parts of food-grade compatibilizer, and 0.8 parts of food-grade lubricant were added and stirred in a high-speed mixer for 10 minutes. The mixture is premixed uniformly at 180°C; the mixture is then fed to a twin-screw extruder, melt-blended at 180°C, extruded into strands, cooled by water, and pelletized to obtain composite masterbatch; the composite masterbatch is fed into a blown film unit, melted and plasticized by the screw at 175°C, and the melt is extruded through an annular die to form a film bubble, which is then air-cooled, shaped, traction-flattened, and wound and slit to obtain the food-grade micro-permeable vacuum packaging bag.

[0015] This invention also provides the application of the above-mentioned preservation method in the transportation or storage of lotus roots.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The nanoemulsion prepared in this invention comprises a browning-responsive chitosan-lotus root polyphenol nanoparticle suspension and a quality change-responsive microgel suspension. Postharvest browning of lotus root is one of the main problems affecting its commercial value. During storage, organic acids (such as citric acid and malic acid) produced by the lotus root's own respiration metabolism, as well as organic acids that rapidly accumulate after cell damage at the damaged areas, are easily enriched and retained in the nodes, unable to diffuse quickly. This leads to a drop in local pH at the nodes to below 5.5. The browning-responsive system is prepared by ion-electrostatic cross-linking of chitosan and sodium tripolyphosphate. The cross-linked structure is stable in a neutral environment. When the pH drops below 5.5, high concentrations of hydrogen ions break the ionic bonds, triggering the dissociation of the chitosan-sodium tripolyphosphate nanoparticle ion-cross-linked structure. The encapsulated lotus root polyphenols are rapidly released, scavenging free radicals such as reactive oxygen species and blocking browning at its source. At the same time, it competes with the lotus root's own polyphenols for PPO active sites, directly inhibiting polyphenol growth. The catalytic activity of oxidases prevents the formation of quinones and melanin, and the response mechanism occurs before the irreversible browning. During the harvesting, cleaning and processing of lotus root, a certain number of spoilage microorganisms are attached. When stored at 4±1℃, these microorganisms continue to metabolize. As time goes on, their total number of colonies gradually accumulates and secretes extracellular proteases. The qualitative change response system is highly sensitive to proteases. Before the spoilage microorganisms have multiplied to the point of lotus root spoilage, the trace amount of extracellular proteases secreted by them can cause local degradation of the gelatin skeleton, triggering microgel rupture and releasing Lactobacillus plantarum. Lactobacillus plantarum continues to metabolize and produce lactic acid, which further reduces the local microenvironment pH of lotus root. On the one hand, it directly inhibits the proliferation of spoilage microorganisms, and on the other hand, it promotes the simultaneous release of lotus root polyphenols from the surrounding undisintegrated browning response system. Lotus root polyphenols and Lactobacillus plantarum form a synergistic antibacterial response mechanism. The response occurs in the early stage of spoilage bacterial colonization and before the lotus root shows sensory spoilage. The nanoemulsion prepared by this invention has an average particle size of 50-150 nm and a stable pH of 6.5-7.0, which is close to the initial pH of intact lotus root tissue. The effective components are firmly encapsulated inside the carrier, and the effective components will not dissolve and be lost prematurely during the lotus root processing. By piercing 4-6 mm micropores in the lotus root nodes with a 0.5-0.8 mm fine needle, and then using a low-temperature vacuum impregnation process, the gas inside the lotus root tissue is extracted during the vacuum stage, and negative pressure is formed in the micropores and intercellular spaces of the lotus root. After the pressure returns to normal, the nanoemulsion is pressed into the internal tissue of the lotus root by the pressure difference. It can cover the lotus root skin and also wet the micropores and thin-walled channels inside the lotus root nodes, achieving full coverage of the nanoemulsion from the inside out. It can precisely enrich the preservative active ingredients in the lotus root nodes and damaged parts that are most prone to spoilage, filling the preservation gaps inside the lotus root tissue. The food-grade micro-permeable vacuum packaging bag of this invention incorporates lotus root residue microcrystalline cellulose, which has multiple synergistic preservation advantages: ordinary pure low-density polyethylene resin film has low oxygen permeability, which affects the activity of Lactobacillus plantarum. This invention incorporates O-MCC into the resin matrix, forming uniform and controllable micro-permeable channels through the cellulose pores, allowing micro-oxygen to pass through and expelling carbon dioxide produced by lotus root respiration, thus constructing a micro-aerobic environment suitable for the survival of Lactobacillus plantarum, ensuring that the live bacteria continuously produce acid and release polyphenols to inhibit bacteria; at the same time, O-MCC is derived from lotus root processing by-products, realizing waste recycling, which is green, low-carbon, and meets food packaging safety requirements. The nanoemulsion of this invention forms a synergistic preservation system with a food-grade micro-permeable vacuum packaging bag. The nanoemulsion responds to pH changes on the surface and inside of the lotus root, inhibiting the deterioration of the lotus root in stages, while the micro-permeable vacuum packaging bag isolates external pollution and provides a micro-aerobic environment suitable for the survival of Lactobacillus plantarum, significantly improving the overall preservation effect. Detailed Implementation

[0017] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] It should be understood that the following limitations on the types, addition ratios, and process parameters of substances in the preparation process of the nanoemulsion and food-grade micro-permeable vacuum packaging bags in this invention are preferred embodiments and should not be construed as limiting the scope of protection of the independent claims. The embodiments described are only for explaining the invention and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available food-grade reagents and materials. The oxygen concentration in the microaerobic environment of this invention is defined as 2-5%. Example 1 Preparation of nanoemulsion

[0019] S1: Collect lotus root peel, nodes, and residue (collectively referred to as "lotus root processing by-products") generated during lotus root processing. Remove moldy and rotten parts, wash with clean water, and drain. Chop the washed by-products into small pieces with a particle size of 1 cm. Add a 30% ethanol solution (solid-to-liquid ratio 1:20), adjust the pH to 3.0 with citric acid, and place the mixture in an ultrasonic extraction device. Set the ultrasonic power to 300 W and the extraction temperature to 25℃, and perform ultrasonic extraction for 30 min. After extraction, centrifuge at 4000 rpm for 10 minutes. The supernatant was collected and concentrated under reduced pressure at 40℃ to 1 / 5 of its original volume to obtain lotus root polyphenol extract. The total phenol content was determined to be 0.3% (calculated as gallic acid equivalent). Chitosan was dissolved in a 1% (v / v) glacial acetic acid solution and stirred until completely dissolved to prepare a 0.3% (w / w) chitosan solution. The lotus root polyphenol extract was added to sterile water to prepare a 0.2% (w / w) lotus root polyphenol extract solution. The chitosan solution and lotus root polyphenol extract solution were thoroughly mixed, and a 0.4% (w / w) sodium tripolyphosphate solution was slowly added dropwise at a rate of 1 mL / min while stirring at 300 rpm. Stirring was continued for 30 min, and the pH of the system was adjusted to 6.5 to obtain a chitosan-lotus root polyphenol nanoparticle suspension. The mass ratio of the chitosan solution, lotus root polyphenol extract solution, and sodium tripolyphosphate solution was 1:0.5:0.2. S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 8 CFU / mL was used to obtain a bacterial suspension. The bacterial suspension was mixed with a 5% gelatin solution preheated to 40°C at a volume ratio of 1:2, and the pH of the system was adjusted to 6.2. At 4°C, the mixture was slowly and uniformly added dropwise to pre-cooled sterile soybean oil, with the volume of soybean oil being three times that of the mixture. After the addition was complete, the mixture was allowed to stand at 4°C for 10 minutes to solidify, and then stirred at 350 rpm for 15 minutes to form gelatin microspheres. Most of the upper soybean oil layer was removed, and 1% (by weight of the total dry gelatin mass) of transglutaminase was added. The mixture was cross-linked at 30°C for 1.5 hours. The microgel was collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4°C containing 0.05% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel was resuspended in a small amount of sterile water to make the mass fraction of the microgel suspension 10%. S3: Add liquid soybean lecithin to soybean oil at a volume ratio of 1:20 and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:2 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at 10,000 rpm using a high-speed shear mill, and continue shearing for 5 minutes to obtain a crude emulsion; homogenize the crude emulsion twice at 60 MPa using a high-pressure homogenizer, and then rapidly cool it to below 25°C. Slowly add the microgel suspension at 200 rpm, continue stirring for 5 minutes, and adjust the pH of the system to 6.5 to obtain the nanoemulsion, wherein V 油相 V 初始水相 V 微凝胶悬液 =1 : 6 : 0.8. Example 2 Preparation of Nanoemulsion

[0020] S1: Collect lotus root peel, nodes, and residue (collectively referred to as "lotus root processing by-products") generated during lotus root processing. Remove moldy and rotten parts, wash with clean water, and drain. Chop the washed by-products into small pieces with a particle size of 1 cm. Add a 30% ethanol solution (solid-to-liquid ratio 1:20), adjust the pH to 3.0 with citric acid, and place the mixture in an ultrasonic extraction device. Set the ultrasonic power to 300 W and the extraction temperature to 25℃, and perform ultrasonic extraction for 30 min. After extraction, centrifuge at 4000 rpm for 10 minutes. The supernatant was collected and concentrated under reduced pressure at 40℃ to 1 / 5 of its original volume to obtain lotus root polyphenol extract. The total phenol content was determined to be 0.3% (calculated as gallic acid equivalent). Chitosan was dissolved in a 1% (v / v) glacial acetic acid solution and stirred until completely dissolved to prepare a 0.3% (w / w) chitosan solution. The lotus root polyphenol extract was added to sterile water to prepare a 0.3% (w / w) lotus root polyphenol extract solution. The chitosan solution and lotus root polyphenol extract solution were thoroughly mixed, and a 0.4% (w / w) sodium tripolyphosphate solution was slowly added dropwise at a rate of 1.5 mL / min while stirring at 400 rpm. Stirring was continued for 40 min, and the pH of the system was adjusted to 6.7 to obtain a chitosan-lotus root polyphenol nanoparticle suspension. The mass ratio of chitosan solution, lotus root polyphenol extract solution, and sodium tripolyphosphate solution was 1:0.8:0.3. S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 9CFU / mL was used to obtain a bacterial suspension. The bacterial suspension was mixed with a 7% gelatin solution preheated to 40°C at a volume ratio of 1:3, and the pH of the system was adjusted to 6.5. At 4°C, the mixture was slowly and uniformly added dropwise to pre-cooled sterile corn oil, with the volume of corn oil being four times that of the mixture. After the addition was complete, the mixture was allowed to stand at 4°C for 12 minutes to solidify, and then stirred at 400 rpm for 20 minutes to form gelatin microspheres. Most of the upper corn oil layer was removed, and 1.3% (by weight of the total dry gelatin mass) of transglutaminase was added. The mixture was cross-linked at 32°C for 1.7 hours. The microgel was collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4°C containing 0.07% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel was resuspended in sterile water to a mass fraction of 12%. S3: Add liquid soybean lecithin to soybean oil at a volume ratio of 1:30 and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:3 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at 11000 rpm using a high-speed shear mill, and continue shearing for 7 min to obtain a crude emulsion; homogenize the crude emulsion three times at 75 MPa using a high-pressure homogenizer, and then rapidly cool it to below 25°C. Slowly add the microgel suspension at 240 rpm, continue stirring for 7 min, and adjust the pH of the system to 6.7 to obtain the nanoemulsion, wherein V 油相 V 初始水相 V 微凝胶悬液 =1 : 8 : 1.2. Example 3 Preparation of Nanoemulsion

[0021] S1: Collect lotus root peel, nodes, and residue (collectively referred to as "lotus root processing by-products") generated during lotus root processing. Remove moldy and rotten parts, wash with clean water, and drain. Chop the washed by-products into small pieces with a particle size of 1 cm. Add a 30% ethanol solution (solid-to-liquid ratio 1:20), adjust the pH to 3.0 with citric acid, and place the mixture in an ultrasonic extraction device. Set the ultrasonic power to 300 W and the extraction temperature to 25℃, and perform ultrasonic extraction for 30 min. After extraction, centrifuge at 4000 rpm for 10 minutes. The supernatant was collected and concentrated under reduced pressure at 40℃ to 1 / 5 of its original volume to obtain lotus root polyphenol extract. The total phenol content was determined to be 0.3% (calculated as gallic acid equivalent). Chitosan was dissolved in 1% glacial acetic acid solution and stirred until completely dissolved to prepare a 0.3% chitosan solution. The lotus root polyphenol extract was added to sterile water to prepare a 0.4% lotus root polyphenol extract solution. The chitosan solution and lotus root polyphenol extract solution were thoroughly mixed, and a 0.4% sodium tripolyphosphate solution was slowly added dropwise at a rate of 2 mL / min while stirring at 450 rpm. Stirring was continued for 50 min, and the pH of the system was adjusted to 6.8 to obtain a chitosan-lotus root polyphenol nanoparticle suspension. The mass ratio of chitosan solution, lotus root polyphenol extract solution, and sodium tripolyphosphate solution was 1:1.2:0.3. S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 9 CFU / mL was used to obtain a bacterial suspension. The bacterial suspension was mixed with an 8% gelatin solution preheated to 40°C at a volume ratio of 1:3, and the pH of the system was adjusted to 6.7. At 4°C, the mixture was slowly and uniformly added dropwise to pre-cooled sterile sunflower seed oil, with the volume of sunflower seed oil being 5 times that of the mixture. After the addition was complete, the mixture was allowed to stand at 4°C for 14 min to solidify, and then stirred at 450 rpm for 22 min to form gelatin microspheres. Most of the upper layer of sunflower seed oil was separated and removed. 1.7% (by weight of the total dry gelatin mass) of transglutaminase was added, and the mixture was cross-linked at 33°C for 1.8 h. The microgel was collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4°C containing 0.08% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel was resuspended in sterile water to a mass fraction of 14%. S3: Add liquid soybean lecithin to soybean oil at a volume ratio of 1:40 and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:3 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at 11000 rpm using a high-speed shear mill, and continue shearing for 8 minutes to obtain a crude emulsion; homogenize the crude emulsion three times at 85 MPa using a high-pressure homogenizer, and then rapidly cool it to below 25°C. Slowly add the microgel suspension at 280 rpm, continue stirring for 8 minutes, and adjust the pH of the system to 6.8 to obtain the nanoemulsion, wherein V 油相 V 初始水相 V 微凝胶悬液 =1 : 9 : 1.3. Example 4 Preparation of Nanoemulsion

[0022] S1: Collect lotus root peel, nodes, and residue (collectively referred to as "lotus root processing by-products") generated during lotus root processing. Remove moldy and rotten parts, wash with clean water, and drain. Chop the washed by-products into small pieces with a particle size of 1 cm. Add a 30% ethanol solution (solid-to-liquid ratio 1:20), adjust the pH to 3.0 with citric acid, and place the mixture in an ultrasonic extraction device. Set the ultrasonic power to 300 W and the extraction temperature to 25℃, and perform ultrasonic extraction for 30 min. After extraction, centrifuge at 4000 rpm for 10 minutes. After 1 minute, the supernatant was collected and concentrated under reduced pressure at 40℃ to 1 / 5 of its original volume to obtain lotus root polyphenol extract. The total phenol content was determined to be 0.3% (calculated as gallic acid equivalent). Chitosan was dissolved in 1% glacial acetic acid solution and stirred until completely dissolved to prepare a 0.3% chitosan solution. The lotus root polyphenol extract was added to sterile water to prepare a 0.5% lotus root polyphenol extract solution. The chitosan solution and the lotus root polyphenol extract solution were thoroughly mixed, and 0.4% sodium tripolyphosphate solution was slowly added dropwise at a rate of 2 mL / min while stirring at 500 rpm. The stirring was continued for 60 minutes, and the pH of the system was adjusted to 7.0 to obtain a chitosan-lotus root polyphenol nanoparticle suspension. The mass ratio of chitosan solution, lotus root polyphenol extract solution and sodium tripolyphosphate solution was 1:1.5:0.4. S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 10CFU / mL was used to obtain a bacterial suspension. The bacterial suspension was mixed with a 10% gelatin solution preheated to 40°C at a volume ratio of 1:4, and the pH of the system was adjusted to 6.8. At 4°C, the mixture was slowly and uniformly added dropwise to pre-cooled sterile peanut oil, with the volume of peanut oil being 6 times that of the mixture. After the addition was complete, the mixture was allowed to stand at 4°C for 15 minutes to solidify, and then stirred at 500 rpm for 25 minutes to form gelatin microspheres. Most of the upper peanut oil layer was removed, and 2% (by weight of the total dry gelatin mass) of transglutaminase was added. The mixture was cross-linked at 35°C for 2 hours. The microgel was collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4°C containing 0.1% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel was resuspended in sterile water to a mass fraction of 15%. S3: Add liquid soybean lecithin to soybean oil at a volume ratio of 1:50 and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:4 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at 12000 rpm using a high-speed shear mill, and continue shearing for 10 min to obtain a crude emulsion; homogenize the crude emulsion four times at 100 MPa using a high-pressure homogenizer, and then rapidly cool it to below 25°C. Slowly add the microgel suspension at 300 rpm, continue stirring for 10 min, and adjust the pH of the system to 7.0 to obtain the nanoemulsion, wherein V 油相 V 初始水相 V 微凝胶悬液 =1 :10 : 1.5.

[0023] The average particle size of the nanoemulsions prepared in Examples 1-4 was determined by dynamic light scattering method, and the results are shown in Table 1.

[0024] Table 1. Average Particle Size of Nanoemulsions

[0025] Test results show that the average particle size of the nanoemulsions prepared in Examples 1-4 all fall within the range of 50-150 nm. The emulsion droplets are small in size and can easily penetrate into the internal tissue of the lotus root through the 0.5-0.8 mm puncture micropores of the lotus root nodes. Example 5: Preparation of food-grade micro-permeable vacuum packaging bags

[0026] Fresh lotus root residue was washed, drained, dried at 70℃ to constant weight, and pulverized through an 80-mesh sieve. A composite alkali solution was prepared by mixing 1.0 mol / L NaOH solution and 0.5 mol / L Na₂SO₃ solution at a volume ratio of 1:2. The lotus root residue powder was mixed with the composite alkali solution at a mass-volume ratio of 1 g:10 mL, stirred in a water bath at 75℃ for 3 hours, and then filtered. The solid was repeatedly washed with deionized water until neutral. The solid was hydrolyzed with 5% hydrochloric acid at 70℃ for 80 minutes, with a solid-to-hydrochloric acid mass-volume ratio of 1 g:15 mL. After filtration, the solid was washed with deionized water until neutral, dried at 60℃, and then ultra-finely pulverized to obtain lotus root residue microcrystalline fibers. O-MCC powder; based on 100 parts by weight of food-grade low-density polyethylene resin, 10 parts of O-MCC powder dried at 65℃ for 6 hours, 3 parts of food-grade compatibilizer maleic anhydride grafted polyethylene, and 0.8 parts of food-grade lubricant oleamide are added and stirred in a high-speed mixer for 10 minutes to complete uniform premixing; the mixture is conveyed to a twin-screw extruder, melt-blended at 180℃, extruded into strands, water-cooled, and pelletized to obtain composite masterbatch; the composite masterbatch is fed into a blown film unit, melt-plasticized in the screw at 175℃, the melt is extruded through an annular die to form film bubbles, and air-cooled for shaping, traction flattening, winding and slitting are used to obtain the food-grade micro-permeable vacuum packaging bag.

[0027] The performance of the prepared food-grade micro-permeable vacuum packaging bag was compared with that of pure food-grade low-density polyethylene vacuum packaging bag. The results are shown in Table 2.

[0028] Table 2. Performance Test Table for Vacuum Packaging Bags

[0029] Oxygen and water vapor permeability were measured under standard conditions of 23℃ and 50% relative humidity, with five parallel tests per group and the average value taken. The oxygen permeability of pure food-grade low-density polyethylene vacuum packaging bags is significantly lower than that of the micro-permeable vacuum packaging bags of this invention, which inhibits the activity of *Lactobacillus plantarum*. In contrast, the vacuum packaging bags of this invention utilize the microcrystalline cellulose of lotus root residue to form uniform micro-gas exchange channels, providing a small amount of oxygen and expelling carbon dioxide produced by lotus root respiration, thus meeting the microaerophilic survival conditions of *Lactobacillus plantarum*. The water vapor permeability data shows that the vacuum packaging bags of this invention can promptly remove accumulated condensate from the bag, reducing the growth of miscellaneous bacteria caused by high humidity and water accumulation. Example 6: A method for preserving whole lotus root with skin

[0030] Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. Using a sterile fine needle with a diameter of 0.5 mm, pierce 4 mm deep at the nodes of the whole lotus root with skin. Make 4 holes evenly in each node. Immerse the lotus root completely in the nanoemulsion prepared in Example 1 at a mass ratio of lotus root to nanoemulsion of 1:3. Vacuum the lotus root to a vacuum degree of 0.08 MPa at 4°C and maintain it for 10 min. Then continue to soak at normal pressure for 15 min. Remove the lotus root and air dry it at 4°C for 30 min. The processed lotus root was placed in the food-grade micro-permeable vacuum packaging bag prepared in Example 5, and then vacuumed and sealed. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity. Example 7: A method for preserving whole lotus root with skin

[0031] Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. A sterile needle with a diameter of 0.6 mm was used to pierce 5 mm deep at each node of the whole lotus root with skin. Five holes were evenly pierced at each node. The lotus root was completely immersed in the nanoemulsion prepared in Example 2 at a mass ratio of lotus root to nanoemulsion of 1:4. The vacuum was drawn to a vacuum degree of 0.08 MPa at 6°C and maintained for 20 min. Then, it was soaked at normal pressure for another 20 min. The lotus root was then removed and dried in a ventilated place at 10°C for 40 min. The processed lotus root was placed in the food-grade micro-permeable vacuum packaging bag prepared in Example 5, and then vacuumed and sealed. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity. Example 8: A method for preserving whole lotus root with skin

[0032] Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. A sterile fine needle with a diameter of 0.7 mm was used to pierce 5 mm deep at the nodes of the whole lotus root with skin. Five holes were evenly pierced at each node. The lotus root was completely immersed in the nanoemulsion prepared in Example 3 at a mass ratio of lotus root to nanoemulsion of 1:3. The vacuum was drawn to a vacuum degree of 0.09 MPa at 6°C and maintained for 23 min. Then, it was soaked at normal pressure for another 22 min. The lotus root was then removed and dried in a ventilated place at 15°C for 45 min. The processed lotus root was placed in the food-grade micro-permeable vacuum packaging bag prepared in Example 5, and then vacuumed and sealed. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity. Example 9: A method for preserving whole lotus root with skin

[0033] Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. A sterile fine needle with a diameter of 0.8 mm was used to pierce 5 mm deep at the nodes of the whole lotus root with skin. Six holes were evenly pierced at each node. The lotus root was completely immersed in the nanoemulsion prepared in Example 3 at a mass ratio of lotus root to nanoemulsion of 1:5. The vacuum was drawn to a vacuum degree of 0.09 MPa at 8°C and maintained for 25 min. Then, it was soaked at normal pressure for another 25 min. The lotus root was then removed and dried in a ventilated place at 18°C ​​for 50 min. The processed lotus root was placed in the food-grade micro-permeable vacuum packaging bag prepared in Example 5, and then vacuumed and sealed. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity. Example 10: A method for preserving whole lotus root with skin

[0034] Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. A sterile fine needle with a diameter of 0.8 mm was used to pierce 6 mm deep at the nodes of the whole lotus root with skin. Six holes were evenly pierced at each node. The lotus root was completely immersed in the nanoemulsion prepared in Example 4 at a mass ratio of lotus root to nanoemulsion of 1:5. The vacuum was drawn to a vacuum degree of 0.1 MPa at 10°C and maintained for 30 min. Then, it was soaked at normal pressure for another 25 min. The lotus root was then removed and dried in a ventilated place at 20°C for 60 min. The processed lotus root was placed in the food-grade micro-permeable vacuum packaging bag prepared in Example 5, and then vacuumed and sealed. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity. Comparative Example 1: A method for preserving whole lotus roots with skin

[0035] The difference between this comparative example and Example 9 is that the processed lotus root is placed in a pure food-grade low-density polyethylene vacuum packaging bag, while the other conditions are the same as in Example 9. Comparative Example 2: A method for preserving whole lotus roots with skin

[0036] The difference between this comparative example and Example 9 is that the lotus root is not immersed in the nanoemulsion, while the other conditions are the same as in Example 9. Comparative Example 3: A method for preserving whole lotus roots with skin

[0037] The difference between this comparative example and Example 9 is that the nanoemulsion lacks the chitosan-lotus root polyphenol nanoparticle suspension; the other conditions are the same as in Example 9. Comparative Example 4: A method for preserving whole lotus roots with skin

[0038] The difference between this comparative example and Example 9 is that the nanoemulsion lacks a microgel suspension, while the other conditions are the same as in Example 9.

[0039] Lotus roots from Examples 6-10 and Comparative Examples 1-4 were stored for 35 days after preservation treatment. The Lab value (L* value and a* value), browning index, PPO activity, weight loss rate and hardness of the lotus roots were measured. The results are shown in Table 3.

[0040] Table 3. Data on relevant indicators of lotus root stored for 35 days

[0041] Table 3 shows that all indicators of the embodiments are significantly better than those of the comparative examples, with Example 9 showing the best effect. Comparative Example 1 used a pure food-grade low-density polyethylene vacuum packaging bag with an oxygen permeability of 510 cm³ / (m²・24h). Headspace gas analysis confirmed that after packaging lotus root and refrigerating it, the oxygen consumption inside the bag was reduced to below 1%, and hypoxia stress induced an increase in PPO activity. At the same time, the metabolic activity of *Lactobacillus plantarum* was also affected to some extent, resulting in a decrease in the overall preservation effect. In contrast, the oxygen permeability of the micro-permeable vacuum packaging bag of the present invention was 1650 cm³ / (m²・24h). The oxygen consumption rate (cm³ / (m²・24h)) reached a dynamic equilibrium with the respiration oxygen consumption rate of whole lotus roots stored at 4℃ with skin. Headspace gas analysis confirmed that it could stably maintain a microaerophilic environment of 2-5%. Comparative Example 2 did not undergo nanoemulsion impregnation treatment on the lotus roots and lacked both the browning response system (chitosan-lotus root polyphenol nanoparticle suspension) and the quality change response system (microgel suspension). It exhibited the most severe browning and significant loss of flesh crispness, resulting in the worst overall preservation effect. Comparative Example 3's nanoemulsion did not contain chitosan-... The lotus root polyphenol nanoparticle suspension could not effectively inhibit PPO activity, and the browning degree of lotus root was significantly aggravated. The nanoemulsion of Comparative Example 4 did not add microgel suspension and lacked long-lasting antibacterial active components. During storage, the browning of lotus root was aggravated, the enzyme activity was high, and the flesh softened severely. However, in the example, with the synergy of nanoemulsion and micro-permeable vacuum packaging bag, the lotus root had high brightness and mild browning degree after 35 days of storage. PPO activity was effectively inhibited, the weight loss was small, the flesh firmness was well preserved, and the long-term preservation advantage was outstanding.

[0042] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preserving whole lotus roots with skin, characterized in that, Includes the following steps: Select freshly harvested, whole lotus roots with skin, free from mechanical damage, pests and diseases, and of uniform size; Wash the mud off the whole lotus root with skin, remove the head and roots, and keep the whole lotus root nodes. Using a sterile fine needle with a diameter of 0.5-0.8 mm, pierce the nodes of the whole lotus root with skin into a depth of 4-6 mm, and evenly pierce 4-6 holes in each node. Completely immerse the lotus root in the nano-emulsion, and vacuum it at 4-10℃ to a vacuum degree of 0.08-0.1 MPa for 10-30 minutes. Then continue to soak it at normal pressure for 15-25 minutes. Remove the lotus root and air dry it at 4-20℃ for 30-60 minutes. Place the processed lotus root into a food-grade, slightly breathable vacuum packaging bag, vacuum it, and seal it. The vacuum-packed lotus roots were stored at 4±1℃ and 90±5% relative humidity.

2. The preservation method as described in claim 1, characterized in that, In step (3), the mass ratio of lotus root to nanoemulsion is 1:3-5.

3. The preservation method as described in claim 1, characterized in that, The preparation steps of the nanoemulsion in step (3) are as follows: S1: Dissolve chitosan in a 1% (v / v) glacial acetic acid solution and stir until completely dissolved to prepare a 0.3% (w / w) chitosan solution; add lotus root polyphenol extract to sterile water to prepare a 0.2-0.5% (w / w) lotus root polyphenol extract solution; mix the chitosan solution and lotus root polyphenol extract solution thoroughly, and slowly add a 0.4% (w / w) sodium tripolyphosphate solution at a dropping rate of 1-2 mL / min while stirring at 300-500 rpm, continue stirring for 30-60 min, and adjust the pH of the system to 6.5-7.0 to obtain a chitosan-lotus root polyphenol nanoparticle suspension; S2: Take the lyophilized powder of *Lactobacillus plantarum*, inoculate it into MRS liquid medium, and anaerobically culture it at 37℃ for 24 h. After the culture is completed, centrifuge the culture at 5000 rpm for 10 min, collect the bacterial pellet, wash the bacterial cells twice with sterile physiological saline, and then resuspend them with sterile water to adjust the viable count to 1×10⁻⁶. 8 -1×10 10 CFU / mL was used to obtain a bacterial suspension; the bacterial suspension was mixed with a 5-10% gelatin solution preheated to 40℃ at a volume ratio of 1:(2-4), and the pH of the system was adjusted to 6.2-6.8; at 4℃, the mixture was slowly and uniformly added dropwise to pre-cooled sterile vegetable oil, wherein the volume of sterile vegetable oil was 3-6 times that of the mixture. After the addition was completed, the mixture was allowed to stand and solidify at 4℃ for 10-15 min, and then stirred at 350-500 rpm for 15-25 minutes. After 1 minute, gelatin microspheres are formed. Most of the upper vegetable oil is separated and removed. Transglutaminase is added, and the mixture is cross-linked at 30-35℃ for 1.5-2 hours. The microgel is collected by filtration and washed three times with sterile phosphate buffer pre-cooled to 4℃ and containing 0.05-0.1% Tween 80 to thoroughly remove residual oil phase and uncross-linked free gelatin. The washed microgel is resuspended in sterile water to a mass fraction of 10-15%. S3: Add liquid soybean lecithin to soybean oil and stir until completely dissolved to obtain the oil phase; mix chitosan-lotus root polyphenol nanoparticle suspension with sterile water at a volume ratio of 1:2-4 to obtain the initial aqueous phase; slowly add the oil phase to the initial aqueous phase at a high-speed shearing machine speed of 10000-12000 rpm and continue shearing for 5-10 min to obtain a crude emulsion; homogenize the crude emulsion through a high-pressure homogenizer at a pressure of 60-100 MPa 2-4 times, and after homogenization, rapidly cool to below 25℃, slowly add the microgel suspension at a speed of 200-300 rpm, continue stirring for 5-10 min, and adjust the pH of the system to 6.5-7.0 to obtain the nanoemulsion.

4. The preservation method as described in claim 3, characterized in that, The mass ratio of chitosan solution, lotus root polyphenol extract solution and sodium tripolyphosphate solution in S1 is 1 : (0.5-1.5) : (0.2-0.4).

5. The preservation method as described in claim 3, characterized in that, The amount of transglutaminase added in S2 is 1-2% of the total mass of the dried gelatin.

6. The preservation method as described in claim 3, characterized in that, The vegetable oils in S2 include soybean oil, corn oil, sunflower oil, and peanut oil.

7. The preservation method as described in claim 3, characterized in that, The volume ratio of liquid soybean lecithin to soybean oil in S3 is 1:20-50.

8. The preservation method as described in claim 3, characterized in that, V in S3 油相 V 初始水相 V 微凝胶悬液 =1 : (6-10) : (0.8-1.5) The preservation method according to claim 1, characterized in that the preparation method of the food-grade micro-permeable vacuum packaging bag in step (4) is as follows: Fresh lotus root residue was washed, drained, dried at 70℃ to constant weight, and pulverized through an 80-mesh sieve. A 1.0 mol / L NaOH solution and a 0.5 mol / L Na₂SO₃ solution were mixed at a volume ratio of 1:2 to obtain a composite alkali solution. The lotus root residue powder was mixed with the composite alkali solution at a mass-volume ratio of 1 g:10 mL. After stirring in a water bath at 75℃ for 3 hours, the mixture was filtered. The solid was repeatedly washed with deionized water until neutral. The solid was hydrolyzed with 5% hydrochloric acid at 70℃ for 80 minutes, with a solid-to-hydrochloric acid mass-volume ratio of 1 g:15 mL. After filtration, the solid was washed with deionized water until neutral. The solid was dried at 60℃ and ultra-finely pulverized to obtain lotus root residue microcrystalline cellulose O-MCC powder. Based on 100 parts by weight of food-grade low-density polyethylene resin, 10 parts of O-MCC powder dried at 65℃ for 6 hours, 3 parts of food-grade compatibilizer, and 0.8 parts of food-grade lubricant were added and stirred in a high-speed mixer for 10 minutes. The mixture is premixed uniformly at 180°C; the mixture is then fed to a twin-screw extruder, melt-blended at 180°C, extruded into strands, cooled by water, and pelletized to obtain composite masterbatch; the composite masterbatch is fed into a blown film unit, melted and plasticized by the screw at 175°C, and the melt is extruded through an annular die to form a film bubble, which is then air-cooled, shaped, traction-flattened, and wound and slit to obtain the food-grade micro-permeable vacuum packaging bag.

9. The application of the preservation method as described in any one of claims 1-9 in the transportation or storage of lotus root.

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