Marine leafy vegetable modified atmosphere fresh-keeping method based on high-pressure micro-fog humidification

Abstract

The invention discloses a marine leafy vegetable modified atmosphere fresh-keeping method based on high-pressure micro-fog humidification. The fresh green leaf vegetables are stacked and placed in a marine movable air-conditioned cold store (O2, CO2 and N2) at the temperature of 4 DEG C, a high-pressure micro-fog humidifying device containing a nano ZnO-TiO2-chitosan composite sterilization solution is used for humidifying and sterilizing, the humidity is maintained at 85%-90%, and LED composite illumination and UV-C lamp intermittent illumination are combined for corrosion prevention and photocatalysis of TiO2. The method can effectively control water loss and wilting of the leafy vegetables in the storage process, kill microorganisms on the surfaces of the leafy vegetables, inhibit respiration of the leafy vegetables, slow down maturation and decline of the leafy vegetables, maintain the original sensory quality to the maximum extent, and prolong the shelf life of the leafy vegetables by 13 days.

Description

Technical Field

[0001] The present invention belongs to the technical field of fruit and vegetable preservation, and specifically relates to a marine leafy vegetable controlled atmosphere preservation method based on high-pressure micro-mist humidification. Background Art

[0002] During ocean voyages, the preservation and storage of marine leafy vegetables pose more challenges compared to root vegetables or fruits. Leafy vegetables are prone to water loss during storage, resulting in wilting and drying of the leaves. Under conditions of lack of light or poor ventilation, leafy vegetables are prone to yellowing, losing their original green color and affecting the sensory quality. In addition, due to the high water content of leafy vegetables and the relatively enclosed ship environment, molds are likely to grow, leading to the decay and spoilage of vegetables. Even under the best conditions, the storage time of leafy vegetables is relatively short and it is difficult to store them for a long time. Therefore, it is necessary to explore effective preservation technologies to extend the shelf life of leafy vegetables as much as possible to ensure that crew members can obtain fresh green leafy vegetables during ocean voyages and guarantee nutritional intake and health.

[0003] Xie Jing et al. (2023) disclosed "Vegetable Fresh-keeping Transportation Compartment and Its Transportation Method" (Publication No.: CN115782735A). In this method, 36 red-violet and far-infrared composite LED lamps are installed on the inner wall of the transportation compartment body. Irradiation for 6 hours can reduce the total number of microorganisms on the vegetable surface by more than 2.00 log 10 CFU / g and inhibit the virus transmission ability by more than 95%. However, with too many lamps distributed in the box, the thermal effect of far-infrared light may cause the ambient temperature to rise, and leafy vegetables are usually more sensitive. Under the irradiation of far-infrared light, the temperature rise and water loss of the leaves will cause the leaves to become soft and wilt, and the pigments of the leaves may also be affected.

[0004] Liu Huan et al. (2022) disclosed "A Composite Preservative, Preparation Method and a Sprout Fresh-keeping Method" (Publication No.: CN 115005269 A). The composite preservative invented by this method can effectively reduce the decay rate and damage rate in the post-harvest preservation of sprouts through pre-harvest spraying (methyl jasmonate and pea protein) and post-harvest spraying (phytic acid, carboxymethyl chitosan, citral essential oil and glycerol), and synergistic irradiation with LED red and blue lights. However, for vegetables such as sprouts, the problem of water loss is still a key factor. The film layer formed by the post-harvest spraying method of this method is too thin and may not be able to effectively prevent water loss. Moreover, the volatility of components such as citral essential oil and glycerol may cause further water loss on the surface of the sprouts.

[0005] Li Pengxia et al. (2023) disclosed "A Vacuum Precooling and Fresh-keeping Technology for Leafy Vegetables Harvested in High-temperature Seasons" (CN112790242B). In this method, freshly harvested and precooled Shanghai greens are subjected to pressure-maintaining atomization treatment. The atomizing liquid is a fresh-keeping liquid of ε-polylysine, taxifolin, and tannin. The diameter of the atomizing particles is 30 - 40 μm, and the atomization time is 5 min. This method solves the problem of water loss of leafy vegetables during the precooling and pressure-reducing process and plays a role in sterilization and delaying senescence. However, the large diameter of the atomizing particles and the short atomization time may affect the coverage of water on the surface of leafy vegetables and the moisturizing effect.

[0006] Wang Wensheng et al. (2010) disclosed "A Fresh-keeping Method for Broccoli by Supplementary Lighting and Chlorine Dioxide Treatment in a Sub-low-temperature Refrigeration Warehouse" (CN 101253881 B). In this method, a light source is set in a sub-low-temperature refrigeration warehouse, and the broccoli in a polyethylene microporous bag is continuously irradiated with light. Every 24 - 72 h, the sub-low-temperature refrigeration warehouse is disinfected with chlorine dioxide once, and the disinfection treatment time each time is 20 - 40 min. This method can significantly delay the decomposition of chlorophyll in broccoli, keep it green, and control the infection and mildew caused by pathogenic microorganisms. However, chlorine dioxide is a strong irritant gas. Improper handling may cause operators to be exposed to harmful gases, endangering health, and increasing the risk of chemical residues on the surface of vegetables.

[0007] Li Jiangkuo et al. (2023) disclosed "A Microenvironment Modified Atmosphere Fresh-keeping Method for Fresh Daylilies" (CN 113243419B). In this method, a compound anti-aging inhibitor is used to inhibit the enzyme activity of fresh daylilies before harvesting, and a 1-MCP solution is sprayed 1 day before harvesting. Then, the pretreated daylilies are subjected to cold shock treatment with a static magnetic field and a color protection agent for 40 - 60 min and placed in a microenvironment modified atmosphere box. The plasma generator is turned on once every 5 d and runs for 30 min. After sterilization, argon is recharged and sealed for fresh-keeping. The implementation process of this method is complex and cannot prevent water loss of vegetables in the modified atmosphere box. Summary of the Invention

[0008] The purpose of the present invention is to provide a marine leafy vegetable modified atmosphere fresh-keeping method based on high-pressure micro-mist humidification. The present invention adds a nano-ZnO-TiO 2 -chitosan composite bactericidal solution to the purified water of the high-pressure micro-mist humidification device in a marine movable modified atmosphere storage, and combines blue-green LED lights and intermittent UV-C irradiation to preserve leafy vegetables.

[0009] The technical solution of the present invention:

[0010] A marine leafy vegetable modified atmosphere fresh-keeping method based on high-pressure micro-mist humidification mainly includes the following steps:

[0011] (1) Leafy vegetable sorting: Select fresh leafy vegetables with moderate maturity, no wilting or yellowing, no mechanical damage, and no insect infestation;

[0012] (2) Preparation of composite bactericidal and humidifying solution: Mix nano-ZnO, nano-TiO 2 and nano-chitosan particles in a mass ratio of 1:2:1, dissolve them in sterile water to make the solution concentration reach 1% - 2%, continuously stir with a magnetic stirrer for 12 h, and perform 3 homogenization treatments to obtain a nano-ZnO-TiO 2 -chitosan composite bactericidal solution, and place it in a high-pressure micro-mist humidifying device for standby;

[0013] (3) Humidifying treatment: Stack the leafy vegetables selected in step (1) on the shelves of the controlled atmosphere storage. Use the high-pressure micro-mist humidifying device added with the composite bactericidal and humidifying solution in step (2) for automatic intermittent humidification, and maintain the air humidity at 85% - 90%; the controlled atmosphere storage is a marine movable controlled atmosphere storage, and the volume ratio of the filled gas is O 2 : 5%, CO 2 : 5%, N 2 : 90%;

[0014] (4) LED light irradiation: Install LED blue-green lights around the top of the controlled atmosphere storage described in step (3) to provide intermittent light for the leafy vegetables;

[0015] (5) UV-C lamp irradiation: Install a short-wave ultraviolet lamp UV-C at the center position of the top of the controlled atmosphere storage described in step (3) for non-vertical indirect irradiation;

[0016] (6) Storage: Control the storage temperature at 4 °C, ventilate once every 5 days, and refill the regulating gas.

[0017] The preparation method of nano-ZnO described in step (2) mainly includes: Mix 1.0 M zinc nitrate and 2.0 M urea in a volume ratio of 1:1, add 5% (v / v) polyethylene glycol 400, keep stirring at a constant temperature of 95 °C for 4 h to form a precipitate, collect the precipitate by centrifugation, dry it at 80 °C for 3 h, and then calcine it in a muffle furnace at 500 °C for 3 h to finally obtain nano-ZnO powder.

[0018] The preparation method of nano-TiO 2 described in step (2) mainly includes: In an HCl∶H 2 O mixed system with a pH value of 1 - 2, under the condition of constant temperature stirring at 50 °C, gradually add titanium tetraisopropoxide TTIP with a purity of 97%, and control TTIP∶HCl (36 - 38%)∶H 2The molar ratio of O is 0.1∶0.06∶50, and stirring continues until a white viscous precipitate is formed. After reacting for 2 h, the precipitate gradually peptizes to form a transparent sol. After cooling the sol to room temperature, it is dried at 100 °C for 3 h to obtain a xerogel. Then, the xerogel is calcined in a muffle furnace at 500 °C for 3 h, and finally nano-TiO 2 powder is obtained; the concentration of the HCL is 36% - 38%

[0019] The preparation method of the nano-chitosan described in step (2) mainly includes: adding chitosan powder into an appropriate amount of dilute acid solution, stirring until the chitosan is completely dissolved to prepare a uniform chitosan solution with a concentration of 1%, and adjusting the pH to 5.5. Then, a 0.1% sodium tripolyphosphate solution is slowly added to the chitosan solution, gently stirred, the reaction time is controlled to be 1.5 - 2 h, the stirring speed is 500 - 700 rpm. After the reaction ends, the cross-linked chitosan nanoparticles are separated at a centrifugation speed of 8000 - 10000 rpm, the separated nanoparticles are washed with distilled water, and freeze-drying treatment is carried out to obtain nano-chitosan.

[0020] In the controlled atmosphere storage in step (3), a high-pressure micro-mist humidification device is installed and equipped with a humidity sensor. When the sensor detects that the air humidity is lower than 85%, the humidification device is automatically started for humidification. The humidification rate is 4 kg / h, the droplet diameter is 0.5 - 15 μm, and each controlled atmosphere storage is equipped with 2 humidification ports. When the air humidity reaches 90%, the humidification device automatically stops running.

[0021] The LED lamp board described in step (4) is installed around the top of the controlled atmosphere storage, 20 - 30 cm away from the side wall, and 6 are installed in each controlled atmosphere storage; there are two rows of lamp beads on the LED lamp board, and the blue and green lamp beads are evenly arranged alternately. The number of lamp beads is 96, and the ratio is 1:1, the length is 600 mm, and the light intensity is 50 - 100 μmol·m 2 / s; the wavelength of the blue light is 450 - 490 nm, and the wavelength of the green light is 495 - 570 nm; the LED lamp described in step (4) irradiates for 8 - 10 hours every day, and remains off for the rest of the time.

[0022] In step (5), 3 UV-C lamps are installed in each controlled atmosphere storage. Vegetables are not placed in the bottom area of the UV-C lamp to avoid direct irradiation; the length of the UV-C lamp is 300 mm, the wavelength range is 200 - 280 nm, and the irradiation dose is 1 - 3 kJ / m 2 and the light intensity is 0.2 - 1.0 mW / cm 2 ; the UV-C lamp is turned on once every 24 hours, and each irradiation time is 20 - 40 min, and remains off for the rest of the time.

[0023] The beneficial effects of the present invention compared with the prior art are as follows:

[0024] (1) In the leafy vegetable fresh-keeping method provided by the present invention, the fine mist generated by the high-pressure micro-mist humidification device can evaporate quickly, avoiding the formation of water droplets on the surface of fruits and vegetables, and preventing rotting and mold growth caused by water condensation. Micro-mist humidification can significantly reduce the water loss of leafy vegetables. By increasing the humidity, the transpiration of vegetables is weakened and the respiration rate is reduced. This helps to delay their metabolism, reduce the consumption of internal water and nutrients, and thus extend the fresh-keeping period.

[0025] (2) In the leafy vegetable fresh-keeping method provided by the present invention, a nano-scale composite bactericidal and fresh-keeping solution is added to the purified water of the high-pressure micro-mist humidification device. The specific surface area of nano-materials is much larger than that of macroscopic materials, which makes their contact area with the surface of fruits and vegetables larger, enhancing the antibacterial, moisturizing and fresh-keeping effects of the materials. Nano-scale molecules are more likely to penetrate into the micro-structure of fruits and vegetables, thus more effectively playing an antioxidant role. The small particle size of nano-materials enables them to be evenly distributed on the surface of fruits and vegetables, providing a more consistent protection effect and reducing the problem of poor fresh-keeping effect caused by local over-concentration or looseness. The composition of the nano-composite bactericidal solution is nano-ZnO, nano-TiO 2 and nano-chitosan. Nano-ZnO particles have a broad-spectrum antibacterial effect and can effectively inhibit the growth of various pathogenic microorganisms (such as bacteria, molds and yeasts) on the surface of fruits and vegetables. It destroys the cell membrane of microorganisms by generating reactive oxygen species (such as superoxide anions and hydroxyl radicals), resulting in cell death; under ultraviolet light irradiation, TiO 2 nano-particles can produce a strong oxidation effect, generating hydroxyl radicals and other reactive oxygen substances. Vegetables are prone to oxidation reactions during storage, resulting in color change, water loss and loss of nutrients, while the antioxidant activity generated by nano-TiO 2 helps to delay these adverse reactions; the nano-chitosan film has a certain moisturizing ability, which can reduce the water evaporation on the surface of vegetables and prevent the wilting and weight loss of vegetables due to water loss. This is especially important for leafy vegetables because they are prone to quickly lose freshness due to water evaporation. The present invention uses the high-pressure micro-mist humidification device to evenly release the bactericidal solution into the controlled atmosphere storage. The combination of nano-chitosan with nano-ZnO and nano-TiO 2 can form a protective film with antibacterial, antioxidant and moisturizing functions on the surface of vegetables. This protective film can not only block external microorganisms and pollutants, but also maintain the smoothness and brightness of the vegetable surface, extending its market shelf life.

[0026] (3) In the leafy vegetable fresh-keeping method provided by the present invention, the lights of the LED composite light are blue light and green light. During the long-term marine storage process, vegetables are prone to accelerating aging due to water loss, nutrient consumption, and ethylene production. Appropriate supplementary lighting with blue light and green light can help delay these processes. In addition, the storage environment of vegetables may change due to navigation vibration and humidity fluctuations, and LED supplementary lighting can, to a certain extent, make up for the negative impacts brought by these environmental factors. Blue light can reduce the respiration rate of vegetables, delay metabolic activities, reduce the consumption of nutrients, and thus extend the fresh-keeping time. Moreover, it can increase the activity of antioxidant enzymes in vegetables, which helps to scavenge free radicals in cells, prevent oxidative damage to cells, and delay the senescence of vegetables. Blue light can inhibit the growth of surface pathogens at a certain intensity and reduce the incidence of vegetable rot. Green light helps to maintain the green color of leafy vegetables, delay the degradation of chlorophyll, thus avoiding color fading, and green light irradiation can slow down the synthesis of ethylene and delay its ripening and senescence. The combination of blue light and green light used in the present invention can extend the fresh-keeping period of vegetables in multiple aspects.

[0027] (4) In the leafy vegetable fresh-keeping method provided by the present invention, UV-C lamps are used for sterilization and initiating the photocatalytic effect of nano-TiO 2 . UV-C irradiation can effectively kill bacteria, molds, and other microorganisms on the surface of vegetables. Reducing microbial contamination can prevent the spoilage and diseases of vegetables, thereby extending the storage period. In addition, under UV-C light irradiation, the energy gap of TiO 2 is excited, and electrons transition from the valence band to the conduction band, forming electron-hole pairs. The holes react with water molecules to generate hydroxyl radicals, while the electrons react with oxygen to generate superoxide anions. These reactive oxygen species have extremely strong oxidation ability and can effectively destroy the cell membranes, DNA, and protein structures of bacteria and microorganisms, leading to their death. This makes TiO 2 very suitable for surface sterilization under UV-C irradiation. TiO 2 nanoparticles have a long-term antibacterial effect under UV-C irradiation because the photocatalytic effect can continuously activate the surface and ensure its activity.

[0028] (5) The leafy vegetable fresh-keeping method provided by the present invention relies on a movable marine controlled atmosphere storage (O 2 : 5%, CO 2 : 5%, N 2: 90%), spraying a nano-level composite bactericidal and fresh-keeping solution through a micro-mist device, supplemented by the combined treatment of blue-green LED light irradiation and UV-C lamp sterilization. It not only replenishes the water lost by vegetables during storage due to transpiration through a humidification device, alleviating withering and shrinkage, but also forms a physical barrier through a nano-fresh-keeping film, effectively preventing the rapid loss of water and nutrients, thereby helping to maintain the freshness and nutritional value of leafy vegetables. LED blue light and green light, as effective light supplement means, are very suitable for the long-distance storage of green vegetables on ships, helping to delay aging and maintain color. The UV-C lamp can not only directly kill microorganisms, but also maintain the bactericidal effect of TiO 2 In short, this composite ship-controlled atmosphere fresh-keeping technology is very suitable for industrial implementation and can effectively extend the shelf life of leafy vegetables by 13 days. Detailed implementation method

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] In the present invention, the nano-ZnO-TiO 2 -chitosan bactericidal and fresh-keeping solution is prepared in advance: ① Preparation of nano-ZnO: 1.0M zinc nitrate and 2.0M urea are mixed in a volume ratio of 1:1, 5% (v / v) polyethylene glycol 400 is added, and the mixture is kept at a constant temperature and stirred at 95 °C for 4 h, and then a precipitate is obtained. The precipitate is collected by centrifugation and dried at 80 °C for 3 h, and then calcined in a muffle furnace at 500 °C for 3 h, and finally nano-ZnO powder is obtained. ② Preparation of nano-TiO 2 : The water-acid mixture (pH = 1-2) is stirred at a constant temperature of 50 °C, and titanium tetraisopropoxide (TTIP, purity 97%) is added. The molar ratio of TTIP∶HCl (36-38%)∶H 2 O is 0.1∶0.06∶50, and stirring is continued to form a white viscous precipitate. The precipitate gradually peptizes after 2 h, and the transparent sol is cooled to room temperature. The gel is dried at 100 °C for 3 h. Then the dry gel is calcined in a muffle furnace at 500 °C for 3 h, and finally nano-TiO 2 powder is obtained. ③ Preparation of nano-chitosan: Chitosan powder is added to an appropriate amount of dilute acid solution and stirred until the chitosan is completely dissolved to obtain a uniform chitosan solution with a concentration of 1%, and the pH is adjusted to 5.5. A 0.1% sodium tripolyphosphate solution is slowly added to the chitosan solution, gently stirred, with a reaction time of 2 h and a stirring speed of 500 rpm. Then the cross-linked chitosan nanoparticles are separated by centrifugation (8000 rpm), the separated nanoparticles are washed with distilled water, and freeze-dried. ④ The obtained nano-ZnO, nano-TiO 2, Nano chitosan particles are mixed and dissolved in sterile water at a ratio of 1:2:1, with a concentration of 1%. Stir continuously with a magnetic stirrer for 12 h and homogenize 3 times to obtain a nano dispersion with good homogeneity and stability. Finally, directly add the nano dispersion into the high-pressure micro-mist humidification device.

[0031] The LED light board is installed in advance around the top of the controlled atmosphere storage, 20 cm away from the side wall, and 6 are installed in each controlled atmosphere storage. There are two rows of lamp beads on the LED light board, and the blue and green lamp beads are evenly arranged alternately. The number of lamp beads is 96, with a ratio of 1:1, a length of 600 mm, and a light intensity of 50 μmol·m 2 / s. The wavelength of the blue light is 450 - 490 nm, and the wavelength of the green light is 495 - 570 nm. The UV-C lamp is installed in advance at the center of the top of the controlled atmosphere storage, 3 are installed in each controlled atmosphere storage, and no vegetables are placed at the bottom to avoid direct irradiation. The length is 300 mm, the wavelength is 200 - 280 nm, and the irradiation dose is 2 kJ / m 2 , and the light intensity is 0.5 mW / cm 2 .

[0032] Example 1

[0033] A controlled atmosphere preservation method for Shanghaiqing in ships based on high-pressure micro-mist humidification, comprising the following steps:

[0034] (1) Select fresh Shanghaiqing with a straight plant type, plump shape, uniform and shiny leaf color, no yellowing or withering, no shrinkage, damage or discolored spots.

[0035] (2) Stack the selected Shanghaiqing on the shelves of the pre-sterilized controlled atmosphere storage, with 4 kg placed in each basket.

[0036] (3) Fill the controlled atmosphere storage with 5% O 2 , 5% CO 2 , 90% N 2 , and seal it.

[0037] (4) Add a nano ZnO-TiO 2 -chitosan bactericidal and fresh-keeping solution with a final concentration of 1% to the high-pressure micro-mist humidification device. According to the humidity displayed by the humidity sensor, when the air humidity is lower than 85%, automatically humidify at a humidification rate of 4 kg / h, with the diameter of the fog droplets being 0.5 - 15 μm, and 2 humidification ports in each controlled atmosphere storage. Stop humidifying when the air humidity reaches 90%, and maintain the air humidity at 85% - 90%;

[0038] (5) The leafy vegetables are irradiated intermittently with an LED composite light, irradiated for 8 h every 24 h, from 8:00 to 16:00 in the morning, and turned off at other times. The UV-C lamp is irradiated indirectly non-vertically (no vegetables are directly placed at the bottom), turned on once every 24 h, irradiated for 20 - 40 min, and turned off at other times.

[0039] (6) The storage temperature is 4°C, ventilate once every 5 days, and refill with 5% O 2 , 5% CO 2 , 90% N 2 . The storage time is 40 days. Measure the weight loss rate, vitamin C content, chlorophyll retention rate, soluble solids, titratable acid content, ABTS and DPPH free radical scavenging abilities, total colony count and respiration rate of Shanghaiqing when reaching the storage end point.

[0040] The storage results show that compared with the untreated group (control group 1), the shelf life of Shanghaiqing in Example 1 is extended by 15 days, the respiration rate decreases by 18.73%, the total colony count decreases by 43.08%, the weight loss rate decreases by 73.7%, the malondialdehyde content decreases by 18.75%, and the DPPH and ABTS free radical scavenging abilities increase by 9.42% and 12.42% respectively. The nutrients of Shanghaiqing in Example 1 are well maintained, and the chlorophyll, soluble sugar, titratable acid and vitamin contents reach 19.48 mg / 100 g, 1.35%, 0.52% and 28.74 mg / 100 g respectively, which are higher than those of the untreated group. Compared with the single-treatment control groups 2 and 3, the shelf life of Shanghaiqing in Example 1 is extended by 5 days and 11 days respectively. Compared with the single-treatment control groups 4 and 5, the shelf life of Shanghaiqing in Example 1 is extended by 10 days and 8 days respectively. Compared with the untreated group (control group 1), the shelf life of Shanghaiqing in control groups 3, 4 and 5 is extended by 4 days, 5 days and 7 days respectively, indicating that the separate use of composite LED and UV-C light illumination, high-pressure micro-mist humidification and nano-preservation bactericidal liquid is effective for the preservation of Shanghaiqing. And the preservation effect of control group 2 on Shanghaiqing is higher than that of control groups 4 and 5, indicating that the combined use of high-pressure micro-mist humidification and nano-preservation bactericidal liquid has the best effect.

[0041] Example 2

[0042] A marine spinach controlled atmosphere preservation method based on high-pressure micro-mist humidification, comprising the following steps:

[0043] (1) Select fresh spinach with a straight plant type, plump shape, uniform leaf color and luster, no yellowing or withering, no shrinkage, damage or discoloration spots.

[0044] (2) Stack the selected spinach on the shelves of a pre-disinfected controlled atmosphere storage, with 4 kilograms placed in each basket.

[0045] (3) Fill the controlled atmosphere storage with 5% O 2 , 5% CO 2 , 90% N 2 , and seal.

[0046] (4) Add nano-ZnO-TiO with a final concentration of 1% to the high-pressure micro-mist humidification device2 - Chitosan bactericidal and fresh-keeping solution. According to the humidity displayed by the humidity sensor, when the air humidity is lower than 85%, it automatically humidifies at a humidification rate of 4 kg / h. The diameter of the fog droplets is 0.5 - 15 μm. There are 2 humidification ports in each controlled atmosphere storage. When the air humidity reaches 90%, the humidification stops, and the air humidity is maintained at 85% - 90%.

[0047] (5) The leafy vegetables are irradiated intermittently with LED composite lights for 8 h every 24 h, from 8:00 to 16:00 in the morning, and turned off at other times. The UV-C lamp is irradiated indirectly non-vertically (the vegetables are not directly placed at the bottom), and is turned on once every 24 h for 20 - 40 min, and turned off at other times.

[0048] (6) The storage temperature is 4°C. Ventilate once every 5 days and refill with 5% O 2 、5% CO 2 、90% N 2 . The storage time is 35 days. The weight loss rate, vitamin C content, chlorophyll retention rate, soluble solids, titratable acid content, ABTS and DPPH free radical scavenging abilities, total colony count and respiration rate of spinach are measured when the storage end point is reached.

[0049] The storage results show that compared with the untreated group (control group 6), the shelf life of spinach in Example 2 was extended by 14 d, the respiration rate decreased by 14.13%, the total colony count decreased by 28.84%, the weight loss rate decreased by 73.10%, the malondialdehyde content decreased by 14.29%, and the DPPH and ABTS free radical scavenging abilities increased by 8.63% and 10.37% respectively. The nutrients of spinach in Example 2 were well maintained, and the chlorophyll, soluble sugar, titratable acid and vitamin contents reached 40.19 mg / 100 g, 1.40%, 0.40% and 13.69 mg / 100 g respectively, which were higher than those of the untreated group. Compared with the single-treatment control groups 7 and 8, the shelf life of spinach in Example 2 was extended by 6 d and 12 d. Compared with the single-treatment control groups 9 and 10, the shelf life of spinach in Example 2 was extended by 11 d and 10 d respectively. Compared with the untreated group (control group 6), the shelf life of spinach in control groups 8, 9 and 10 was extended by 2 d, 3 d and 4 d respectively, indicating that the separate use of combined LED and UV-C light irradiation, high-pressure micro-mist humidification and nano fresh-keeping and bactericidal liquid is effective for the preservation of spinach. And the preservation effect of control group 7 on spinach is higher than that of control groups 9 and 10, indicating that the combined use of high-pressure micro-mist humidification and nano fresh-keeping and bactericidal liquid has the best effect.

[0050] Example 3

[0051] A controlled atmosphere preservation method for boat lettuce based on high-pressure micro-mist humidification, comprising the following steps:

[0052] (1) Select fresh lettuce with moderate maturity, no wilting or yellowing, no mechanical damage, and no insect damage.

[0053] (2) Stack the selected lettuce on the shelves of a pre-sterilized controlled atmosphere storage, with 4 kg placed in each basket.

[0054] (3) Fill the controlled atmosphere storage with 5% O 2 , 5% CO 2 , 90% N 2 , and seal it.

[0055] (4) Add a nano-ZnO-TiO 2 -chitosan bactericidal and fresh-keeping solution with a final concentration of 1% to the high-pressure micro-mist humidification device. According to the humidity displayed by the humidity sensor, when the air humidity is lower than 85%, it automatically humidifies at a rate of 4 kg / h. The diameter of the mist droplets is 0.5 - 15 μm, and there are 2 humidification ports in each controlled atmosphere storage. Humidification stops when the air humidity reaches 90%, and the air humidity is maintained at 85% - 90%.

[0056] (5) The leafy vegetables are irradiated intermittently with LED composite lights for 8 h every 24 h, from 8:00 to 16:00 in the morning, and turned off at other times. The UV-C light is irradiated indirectly non-vertically (the vegetables are not directly placed at the bottom), and is turned on once every 24 h for 20 - 40 min, and turned off at other times.

[0057] (6) The storage temperature is 4°C. Ventilate once every 5 days and refill the gas with 5% O 2 , 5% CO 2 , 90% N 2 . The storage time is 35 days. Measure the weight loss rate, vitamin C, malondialdehyde content, chlorophyll content, soluble solids, titratable acid content, ABTS and DPPH free radical scavenging ability, total colony count, and respiration rate of the lettuce when reaching the storage end point.

[0058] The storage results showed that, compared with the untreated group (control group 11), the shelf life of the lettuce in Example 3 was extended by 13 days, the respiratory rate decreased by 22.44%, the total colony count decreased by 21.04%, the weight loss rate decreased by 71.29%, the malondialdehyde content decreased by 26.09%, and the DPPH and ABTS free radical scavenging capacities increased by 10.04% and 7.22% respectively. The nutrients in the lettuce of Example 3 were well maintained, and the chlorophyll, soluble sugar, titratable acid and vitamin contents reached 28.77 mg / 100 g, 1.50%, 0.34% and 10.94 mg / 100 g respectively, which were higher than those of the untreated group. Compared with the single-treatment control groups 12 and 13, the shelf life of the lettuce in Example 3 was extended by 5 days and 10 days. Compared with the single-treatment control groups 14 and 15, the shelf life of the lettuce in Example 3 was extended by 9 days and 10 days respectively. Compared with the untreated group (control group 11), the shelf life of the lettuce in control groups 13, 14 and 15 was extended by 3 days, 4 days and 3 days respectively, indicating that the separate use of combined LED and UV-C light illumination, high-pressure micro-mist humidification and nano-preservation bactericidal liquid was effective for the preservation of lettuce. The preservation effect of control group 12 on lettuce was higher than that of control groups 14 and 15, indicating that the combined use of high-pressure micro-mist humidification and nano-preservation bactericidal liquid had the best effect.

[0059] Table 1 shows the initial values of three example samples of Shanghaiqing, spinach and lettuce. In Table 2, control 1 was Shanghaiqing that was stored under 4°C controlled atmosphere without high-pressure micro-mist humidification and without combined LED and UV-C light illumination, and the other steps were the same as those in Example 1; control 2 was Shanghaiqing that was stored under 4°C controlled atmosphere with only high-pressure micro-mist humidification (including nano-preservation bactericidal liquid) and without combined LED and UV-C light illumination, and the other steps were the same as those in Example 1; control 3 was Shanghaiqing that was stored under 4°C controlled atmosphere with only combined LED and UV-C light illumination and without high-pressure micro-mist humidification, and the other steps were the same as those in Example 1. Control 4 was Shanghaiqing that was stored under 4°C controlled atmosphere with only high-pressure micro-mist humidification but without nano-preservation bactericidal liquid (replaced with distilled water) and without combined LED and UV-C light illumination, and the other steps were the same as those in Example 1. Control 5 was Shanghaiqing that was stored under 4°C controlled atmosphere with only nano-preservation bactericidal liquid (manually sprayed) but without a high-pressure micro-mist device and without combined LED and UV-C light illumination, and the other steps were the same as those in Example 1.

[0060] The implementation methods of control 6 and control 11 were the same as that of control 1, with the samples replaced by spinach and lettuce respectively. The implementation methods of control 7 and control 12 were the same as that of control 2, with the samples replaced by spinach and lettuce respectively. The implementation methods of control 8 and control 13 were the same as that of control 3, with the samples replaced by spinach and lettuce respectively. The implementation methods of control 9 and control 14 were the same as that of control 4, with the samples replaced by spinach and lettuce respectively. The implementation methods of control 10 and control 15 were the same as that of control 5, with the samples replaced by spinach and lettuce respectively.

[0061] Table 1 Results of various indicators of vegetables in different embodiments on the 0th day of storage

[0062]

[0063]

[0064] Table 2 Results of various indicators of vegetables in different embodiments and control examples at the end of the shelf life

[0065]

[0066]

[0067] It can be seen from the content of Table 1 and Table 2 above that the high-pressure micro-mist humidification - LED composite lighting combined with UV-C lamp synergistic ship-controlled atmosphere fresh-keeping technology can significantly reduce the water loss rate of leafy vegetables, inhibit the respiration rate of leafy vegetables, inhibit the growth of colonies, and inhibit the generation of malondialdehyde. Leafy vegetables in the later stage of storage still have relatively high contents of chlorophyll, soluble sugar, titratable acid and vitamin. The shelf life of the samples in the combined treatment group is higher than that in the single treatment group. The micro-mist humidification maintains a high humidity in the storage environment, reduces the water loss of leafy vegetables, and thus reduces the water loss rate. At the same time, the nano-ZnO-TiO 2 -chitosan bactericidal and fresh-keeping solution forms a protective film on the leaves, reducing the evaporation of water. The LED composite lighting with specific light qualities (blue light, green light) reduces the respiration rate of vegetables and delays senescence. At the same time, the appropriate lighting maintains the content of chlorophyll in leafy vegetables, extends the green period of the leaves, and maintains their appearance and nutritional value. The UV-C lamp effectively inhibits the growth of colonies, reduces microbial contamination, and reduces the occurrence of rot and lesions.

Claims

1. A method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification, characterized in that: The main steps include: (1) Leafy vegetable sorting: Select fresh leafy vegetables that are moderately mature, not wilted or yellowed, and not mechanically damaged or infested by insects; (2) Preparation of composite bactericidal humidification solution: Nano ZnO, nano TiO2 and nano chitosan particles were mixed in a mass ratio of 1:2:1, dissolved in sterile water to a solution concentration of 1% to 2%, stirred continuously for 12 h using a magnetic stirrer, and homogenized three times to obtain a nano ZnO-TiO2-chitosan composite bactericidal solution with good uniformity and stability, which was placed in a high-pressure micro-mist humidification device for standby use; (3) Humidification treatment: the leafy vegetables selected in step (1) are stacked and placed on the shelves of a controlled atmosphere storage, and the high-pressure micro-mist humidification device to which the composite sterilization and humidification solution is added in step (2) is used for automatic intermittent humidification, and the air humidity is maintained at 85%-90%; the controlled atmosphere storage is a movable controlled atmosphere storage for ships, and the volume ratio of the gas filled is O2:5%, CO2:5%, and N2:90%; (4) LED lighting: LED blue-green lights are installed around the top of the controlled atmosphere storage in step (3) to provide intermittent lighting for the leafy vegetables; (5) UV-C lamp irradiation: Install a short-wave ultraviolet lamp UV-C at the top center of the controlled atmosphere storage in step (3) to perform non-vertical indirect irradiation; (6) Storage: The storage temperature is controlled at 4°C, and ventilation and refilling with regulated gas are carried out every 5 days.

2. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: The preparation method of nano ZnO in step (2) mainly comprises: mixing 1.0M zinc nitrate and 2.0M urea in a volume ratio of 1:1, adding 5% (v / v) polyethylene glycol 400, maintaining a constant temperature of 95°C with stirring for 4 hours to generate a precipitate, collecting the precipitate by centrifugation, drying it at 80°C for 3 hours, and then calcining it in a muffle furnace at 500°C for 3 hours to finally obtain nano ZnO powder.

3. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: The preparation method of nano-TiO2 described in step (2) mainly comprises: in a HCl:H2O mixed system with a pH value of 1-2, under a constant temperature stirring condition of 50°C, gradually adding 97% pure titanium tetraisopropoxide TTIP, controlling the molar ratio of TTIP:HCl (36-38%):H2O to be 0.1:0.06:50, continuing stirring until a white viscous precipitate is formed, and after reacting for 2 hours, the precipitate gradually peptizes to form a transparent sol; after cooling the sol to room temperature, drying it at 100°C for 3 hours to obtain a dry gel, and then calcining the dry gel in a muffle furnace at 500°C for 3 hours to finally obtain nano-TiO2 powder; the HCL concentration is 36%-38%.

4. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: The preparation method of the nano chitosan described in step (2) mainly comprises: adding chitosan powder to an appropriate amount of dilute acid solution, stirring until the chitosan is completely dissolved, preparing a uniform chitosan solution with a concentration of 1%, and adjusting the pH to 5.5, then slowly adding 0.1% sodium tripolyphosphate solution to the chitosan solution, gently stirring, controlling the reaction time to 1.5 to 2 hours, and the stirring speed to 500 to 700 rpm. After the reaction is completed, separating the chitosan nanoparticles formed by cross-linking at a centrifugal speed of 8000 to 10000 rpm, washing the separated nanoparticles with distilled water, and freeze-drying to obtain nano chitosan.

5. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: In step (3), a high-pressure micro-mist humidification device is installed in the air conditioning storage, and is equipped with a humidity sensor. When the sensor detects that the air humidity is lower than 85%, the humidification device is automatically started for humidification. The humidification rate is 4kg / h, and the droplet diameter is 0.5-15μm. Each air conditioning storage is equipped with 2 humidification ports. When the air humidity reaches 90%, the humidification device automatically stops running.

6. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: The LED light board described in step (4) is installed around the top of the gas conditioning storage, 20 to 30 cm away from the side wall, and 6 are installed in each gas conditioning storage; two rows of lamp beads are arranged on the LED light board, and blue and green lamp beads are evenly and alternately arranged. The number of lamp beads is 96, the ratio is 1:1, the length is 600 mm, and the light intensity is 50-100 μmol·m 2 / s; the wavelength of blue light is 450-490nm, and the wavelength of green light is 495-570nm.

7. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: The LED light in step (4) is irradiated for 8 to 10 hours a day and is turned off for the rest of the time.

8. The method for preserving marine leafy vegetables with controlled atmosphere based on high-pressure micro-mist humidification according to claim 1, characterized in that: In step (5), three UV-C lamps are installed in each gas conditioning storage, and no vegetables are placed in the bottom area of ​​the UV-C lamp to avoid direct irradiation; the length of the UV-C lamp is 300 mm, the wavelength range is 200-280 nm, and the irradiation dose is 1-3 kJ / m 2 , light intensity is 0.2-1.0mW / cm 2 The UV-C lamp is turned on once every 24 hours, with each irradiation time of 20 to 40 minutes, and remains off for the rest of the time.

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