Preparation method and device of micro-nano ozone ice and application of micro-nano ozone ice in pre-cooling of agricultural products

Abstract

The invention relates to the technical field of storage and preservation of agricultural products, in particular to micro-nano ozone ice as well as a preparation method and application thereof. The micro-nano ozone water is prepared by mixing ozone and water at a high speed by using a Venturi ejector. And refrigerating the micro-nano ozone water with the temperature of 2-5 DEG C by using a salt solution (such as NaCl and CaCl2 solutions) with the temperature of-20 DEG C to-40 DEG C as a medium to prepare the micro-nano ozone ice. The process is simple, the refrigeration efficiency is high, and the ozone retention rate is high. Experiments show that the ozone retention rate reaches up to 48.77%, which is much higher than that of the traditional process and contrast. The micro-nano ozone ice is applied to precooling of the litchis, and compared with traditional ice water precooling, the fruit peel browning can be remarkably reduced, and the quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field, and in particular to a method and device for preparing micro-nano ozone ice and application thereof in precooling of agricultural products. Background Art

[0002] Ozone has strong oxidizing properties and can react with microbial membranes to change their permeability, and has the characteristics of broad-spectrum bactericidal. Micro-nano ozone is ozone dispersed in a solution to form micro-nano (1-100μm) tiny bubbles. Its solubility in water is over 95%, and it can exist in the form of stable bubbles for a long time. Due to the physical and chemical characteristics of ozone micro-nano bubbles, such as large specific surface area, strong oxidizing ability, high stability, and easy generation of free radicals, it is often used in sewage treatment and aquaculture.

[0003] Ozone ice is ice made from high-concentration ozone water in different ways, and the half-life of ozone is extended. Ozone ice will continue to release ozone during the melting process, which can kill microorganisms on the surface of aquatic products such as fish and shrimp, thereby extending the shelf life. Patent 201510689759.X discloses an ice containing oxygen as bubbles, which sintered the ozone ice under pressure at 20MPa for 3 hours and then irradiated it with 180-242nm ultraviolet rays. This method has a long production cycle, high cost, and low ozone concentration. "Research on High-Concentration Ozone Ice Production Technology" (Food Industry Science and Technology, 2021, 32(8): 242-245) uses an ozone generator to produce high-concentration ozone gas, and then mixes and dissolves ozone with water through an efficient vortex gas-water mixing pump to obtain high-concentration ozone water. The high-concentration ozone water is then continuously fed into a fast ice maker to make flaky ozone ice. The ozone concentration of the produced ozone ice reaches 16.7mg / L. This method has a high production cost and a low ozone retention rate. The study was able to produce high-concentration ozone water containing 115.3 mg / L of ozone, and then use a fast ice maker to produce ozone ice containing 16.7 mg / L of ozone, with an ozone retention rate of only 14.48%.

[0004] Due to the difficulty in preparing high-concentration ozone water, the low ozone retention rate in ozone ice, the low efficiency of ice preparation and other factors, there are few reports in the field of disinfection, sterilization and preservation of agricultural products. Therefore, it is of great practical significance to provide an ozone ice with high ozone retention rate and low cost and a preparation method thereof, and to widely use it in the preservation and storage of agricultural products.

[0005] Ice water precooling is one of the commonly used precooling methods for agricultural products. Taking litchi as an example, litchi soaked in ice water mixture can quickly remove the field heat of litchi, reduce the respiration rate of litchi, inhibit enzyme and ethylene release, which is of great significance to reduce the rot rate of litchi and improve its quality. At present, there is no report on the use of ozone ice water mixture for precooling of agricultural products such as litchi. Summary of the invention

[0006] In view of this, the present invention provides a method and device for preparing micro-nano ozone ice and its application in precooling agricultural products. The micro-nano ozone ice has a low production cost and a high ozone retention rate. After precooling agricultural products with micro-nano ozone ice, the respiration rate, total number of surface colonies and browning of agricultural products are significantly inhibited, the comprehensive quality of agricultural products is significantly improved, and the shelf life is significantly extended.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The preparation method of micro-nano ozone ice comprises:

[0009] Step A: using a venturi ejector to mix ozone and water at high speed to produce micro-nano ozone water.

[0010] Step B, injecting the micro-nano ozone water into a salt solution at -20°C to -40°C to obtain micro-nano ozone ice;

[0011] The salt solution is an aqueous solution containing NaCl and / or CaCl2.

[0012] In step A of the present invention, the temperature of the water is 2-5°C, specifically 2°C, 3°C, 4°C or 5°C; the pH of the water is 7.0-9.0, specifically 7.0, 9.0, 9.0. Water with a pH of 7.0-9.0 includes pure water with a pH of 7.0 and alkaline water greater than 7.0, which means that the water contains alkaline substances, such as OH - Ions, etc., make the pH of water higher than 7.0.

[0013] In step A of the present invention, the ozone introduction time is 10 to 15 minutes, specifically 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes.

[0014] In step A of the present invention, the pressure of the venturi ejector is 0.3-0.5 MPa, specifically 0.3 MPa, 0.4 MPa, or 0.5 MPa.

[0015] In some embodiments, in step B of the present invention, the salt solution is an aqueous solution containing 20-30wt% NaCl and 20-30wt% CaCl2. In some specific embodiments, in the aqueous solution containing NaCl and CaCl2, the concentrations of NaCl and CaCl2 can be independently selected from 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%.

[0016] In some specific embodiments, the present invention also provides micro-nano ozone ice prepared by the above preparation method.

[0017] The present invention uses a salt solution (such as NaCl and CaCl2 solution) at -20°C to -40°C as a medium to refrigerate micro-nano ozone water at 2 to 5°C to obtain micro-nano ozone ice. The method has a simple preparation process, high refrigeration efficiency, and a high ozone retention rate of 48.77%. In addition, the method does not require an ice maker or a -80°C ultra-low temperature refrigerator, which greatly reduces costs.

[0018] The present invention also provides a device for preparing the above-mentioned micro-nano ozone ice, comprising:

[0019] water storage tanks;

[0020] a control unit in communication with the water storage tank for controlling the generation of ozone and the introduction of ozone into the water storage tank, and

[0021] a micro-nano ozone ice generator connected to the water storage tank;

[0022] The micro-nano ozone ice generator comprises: a quick cooling device containing a -20°C salt solution and a mold placed in the salt solution for molding the micro-nano ozone water.

[0023] Further, the control unit includes: an ozone generator, a venturi ejector;

[0024] The venturi ejector is provided with a water inlet, an air inlet and an ozone water emission port;

[0025] The control unit is connected to the water storage tank through the water inlet and the ozone water emission port of the venturi injector respectively;

[0026] Furthermore, the control unit further comprises a pressure gauge, a flow meter and a water pump arranged between the water inlet of the venturi ejector and the water storage tank;

[0027] A water pump 2 is also provided between the water storage tank and the micro-nano ozone ice reactor to pump the micro-nano ozone water in the water storage tank into the mold of the micro-nano ozone reactor.

[0028] Experiments show that the micro-nano ozone ice prepared by the present invention has an ozone retention rate of more than 50% after being stored at -20°C for 48 hours and an ozone retention rate of more than 28% after being stored for 168 hours. It has good stability and can meet the pre-cooling needs of large quantities of agricultural products (such as lychees).

[0029] The invention also provides the use of the micro-nano ozone ice prepared by the preparation method or the device in the preservation or storage of agricultural products.

[0030] The present invention also provides a method for preserving agricultural products, which is characterized by comprising: precooling the agricultural products using the micro-nano ozone ice prepared by the preparation method or the device.

[0031] In the present invention, the agricultural products include fruits and vegetables;

[0032] The fruits include lychee, longan, rambutan, mangosteen, etc.; the vegetables include cowpea, green bean, bitter melon, cucumber, tomato, etc.

[0033] In some specific embodiments of the present invention, the preprocessing specifically includes:

[0034] The micro-nano ozone ice and water are mixed in a mass ratio of 1:3 to 5 to obtain an ozone ice-water mixture;

[0035] The agricultural products are added into the ozone-ice-water mixture and treated for 10 to 20 minutes.

[0036] In some embodiments of the present invention, the agricultural product is lychee, and the mass ratio of the lychee to the ozone ice-water mixture is 1:(3-10), specifically 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.

[0037] The micro-nano ozone ice provided by the present invention is used to pre-cool litchi. On the one hand, the melting of the micro-nano ozone ice can remove the field heat for the litchi and reduce its respiration. On the other hand, the melting of the micro-nano ozone ice slowly releases ozone, which can kill microorganisms on the surface of the litchi, further reduce the decay of the litchi, and thus extend the shelf life. Experiments show that after the micro-nano ozone ice pre-cooling treatment of the present invention, the total number of colonies decreased by 97.53%, the respiration rate decreased by 24.01%, and the overall quality was significantly improved when the litchi was stored for 11 days, compared with the control group of the pre-cooling treatment of ordinary ice without ozone.

[0038] The present invention also provides a method for precooling agricultural products, which comprises: before storing the agricultural products, using the following method to process:

[0039] The micro-nano ozone ice prepared by the preparation method or the device of the present invention is used to pre-cool agricultural products, or

[0040] The agricultural products are processed by the fresh-keeping method.

[0041] Compared with the traditional precooling method, the present invention has at least one of the following advantages:

[0042] 1) The production cost of micro-nano ozone ice is low and the ozone retention rate is high. The production of the micro-nano ozone ice of the present invention does not require an ice maker or a -80°C ultra-low temperature refrigerator. It uses -20°C supercooled NaCl and CaCl2 solutions as a medium to refrigerate 2°C micro-nano ozone water, with high refrigeration efficiency and an ozone retention rate of up to 48.77%.

[0043] 2) Micro-nano ozone ice has high stability. The prepared micro-nano ozone ice has an ozone retention rate of more than 50% after being stored at -20°C for 48 hours, and an ozone retention rate of more than 28% after 168 hours. It has good stability and can meet the pre-cooling needs of large quantities of lychees and other agricultural products.

[0044] 3) The comprehensive quality of litchi after precooling with the micro-nano ozone ice of the present invention is significantly improved. Compared with the precooling scheme of the traditional ice water precooling and the micro-nano ozone ice prepared with other parameters in the comparative example, the total colony count and respiration rate of litchi after precooling with the micro-nano ozone ice of the present invention decreased more significantly after being stored for 11 days, and the comprehensive quality was higher, thereby extending the shelf life. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The schematic diagram of the device structure for preparing micro-nano ozone ice of the present invention is shown; wherein the components are as follows:

[0046] 1. Water storage tank; 2. Control unit, 21. Ozone generator, 22. Venturi ejector, 23. Pressure gauge, 24. Flow meter, 25. Water pump; 3. Micro-nano ozone ice reactor, 32. Mold (for ozone water molding), 31. Rapid cooling device containing -20℃ salt solution; 4. Water pump;

[0047] Figure 2 The results of ozone concentration and retention rate in different treatment groups are shown. DETAILED DESCRIPTION

[0048] The present invention provides a method and device for preparing micro-nano ozone ice and its application in precooling agricultural products. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0049] The device for preparing micro-nano ozone ice provided by the present invention comprises:

[0050] A water storage tank 1 containing water at 2-5°C and pH 7.0-9.0;

[0051] a control unit 2 connected to the water storage tank 1 and controlling the generation of ozone and passing it into the water storage tank 1, and

[0052] A micro-nano ozone ice generator 3 connected to the water storage tank 1;

[0053] The micro-nano ozone ice generator 3 comprises: a quick cooling device 31 containing a -20°C salt solution and a mold 32 placed in the salt solution for molding the micro-nano ozone water.

[0054] See also Figure 1 In a specific embodiment of the present invention, the device includes a water storage tank 1, a control unit 2 and a micro-nano ozone ice generator 3 respectively connected to the nano-ozone water reactor 1, and a water pump 4 arranged between the water storage tank 1 and the micro-nano ozone ice generator 3.

[0055] The control unit 2 includes an ozone generator 21, a venturi ejector 22, a pressure gauge 23, a flow meter 24 and a water pump 25; wherein the venturi ejector 22 is provided with a water inlet, an air inlet and an ozone water emission port;

[0056] The control unit 2 is connected to the water storage tank 1 through the water inlet and the ozone water emission port of the venturi injector.

[0057] In some other embodiments, the water pump 25 may also be disposed between the control unit 2 and the water storage tank 1 .

[0058] The working principle of the device of the present invention is:

[0059] The water pump 25 pumps the water in the water storage tank into the venturi ejector, the air passes through the ozone generator 21 to generate ozone, and the ozone enters the venturi ejector 22 through the air inlet of the venturi ejector; in the venturi ejector 22, the ozone and water are mixed at a high speed to obtain micro-nano ozone water; the micro-nano ozone water is injected into the water storage tank 1 through the ozone water emission port of the venturi ejector 32, and the micro-nano ozone water in the water storage tank 1 is injected into the mold 32 of the micro-nano ozone ice 3 through the water pump 4; the mold 32 filled with micro-nano ozone water (i.e., the ice mold injected with micro-nano ozone water) is in direct contact with the rapid cooling device 31 filled with -20°C salt solution to quickly form micro-nano ozone ice in the shape of the mold.

[0060] The test materials used in the present invention are all common commercial products and can be purchased in the market.

[0061] The present invention will be further described below in conjunction with embodiments:

[0062] Example 1 Preparation of micro-nano ozone ice

[0063] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a solution containing 23wt% NaCl+23wt% CaCl2 at -20°C, and micro-nano ozone ice is quickly formed.

[0064] Comparative Example 1 Preparation of Micro-Nano Ozone Ice

[0065] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl, and micro-nano ozone ice is quickly formed.

[0066] Comparative Example 2 Preparation of Micro-Nano Ozone Ice

[0067] A venturi ejector was introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it was injected into an ice mold and placed in a -80°C refrigerator to obtain micro-nano ozone ice after 4 hours.

[0068] Comparative Example 3 Preparation of Micro-Nano Ozone Ice

[0069] A venturi ejector was introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. This water was then injected into an ice maker and micro-nano ozone ice was obtained after 30 minutes.

[0070] Comparative Example 4 Preparation of Micro-Nano Ozone Ice

[0071] A venturi ejector is introduced into water at a temperature of 5°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2 to quickly form micro-nano ozone ice.

[0072] Comparative Example 5 Preparation of Micro-Nano Ozone Ice

[0073] A venturi ejector is introduced into water at a temperature of 10°C and a pH of 7 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2 to quickly form micro-nano ozone ice.

[0074] Comparative Example 6 Preparation of Micro-Nano Ozone Ice

[0075] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 5 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2 to quickly form micro-nano ozone ice.

[0076] Comparative Example 7 Preparation of Micro-Nano Ozone Ice

[0077] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 9 and mixed with ozone for 10 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2, quickly forming micro-nano ozone ice.

[0078] Comparative Example 8 Preparation of Micro-Nano Ozone Ice

[0079] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 5 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2 to quickly form micro-nano ozone ice.

[0080] Comparative Example 9 Preparation of Micro-Nano Ozone Ice

[0081] A venturi ejector is introduced into water at a temperature of 2°C and a pH of 7 and mixed with ozone for 15 minutes to form high-concentration micro-nano ozone water. Then it is injected into an ice mold, which is in direct contact with a -20°C supercooled solution containing 23wt% NaCl+23wt% CaCl2 to quickly form micro-nano ozone ice.

[0082] Comparative Example 10 Preparation of ozone-free ice

[0083] Water at a temperature of 2°C and a pH of 7 is injected into an ice mold, which is in direct contact with a solution containing 23wt% NaCl+23wt% CaCl2 at -20°C, rapidly forming ozone-free ice.

[0084] The main parameters involved are shown in Table 1.

[0085] Table 1 Main technical parameters of Example 1 and Comparative Examples 1 to 10

[0086]

[0087] The ozone concentration was measured using the micro-nano ozone ice prepared in Example 1, Comparative Examples 1 to 9, and the ozone-free ice prepared in Comparative Example 10. Ozone retention rate = ozone concentration in ozone ice / ozone concentration in ozone water × 100%. The ozone retention rate results are shown in Figure 1 .

[0088] Depend on Figure 1 It can be seen that the ozone concentration in the micro-nano ozone ice of the embodiment is 15.51 mg / kg, the ozone retention rate is the highest, reaching 48.77%, and the efficiency of preparing micro-nano ozone ice is the highest. Compared with comparative examples 1 to 3, the embodiment has a different ice making method. Compared with the ozone concentration and ozone retention rate in the micro-nano ozone ice, comparative example 3 is the worst, and the cost of the ice making machine is also relatively high.

[0089] Comparative Examples 4 and 5 use water with a temperature higher than that of the embodiment, and the ozone concentration and ozone retention rate of the two are reduced, indicating that the lower the temperature, the higher the efficiency of the prepared micro-nano ozone ice. Comparative Examples 6 and 7 use acidic and alkaline water, and the ozone concentration and ozone retention rate of the two are reduced compared with the embodiment, indicating that water with a neutral pH is more suitable for preparing micro-nano ozone ice. Comparative Examples 8 and 9 use ozone-passing times different from those of the embodiment. The time for ozone-passing in Comparative Example 8 is the shortest, only 5 minutes, and the lowest ozone concentration is 4.53 mg / kg, indicating that insufficient ozone-passing time will seriously affect the ozone concentration in the micro-nano ozone ice. The time for ozone-passing in Comparative Example 9 is up to 15 minutes. Although the ozone concentration in the micro-nano ozone ice is significantly improved, the ozone retention rate has dropped to 34.42%, which is not efficient. The above results show that the micro-nano ozone ice prepared by the present invention using a specific temperature, a specific pH and a specific ozone-passing time has an ozone concentration and an ozone retention rate that are significantly higher than those of Comparative Examples 1-10.

[0090] Test case: Application in precooling of agricultural products

[0091] Taking litchi as an example, the application of the prepared micro-nano ozone ice in precooling agricultural products was carried out. The litchi was precooled using the micro-nano ozone ice prepared in Example 1 and the ozone-free ice prepared in Comparative Example 10 and then stored at low temperature. The specific method is: the micro-nano ozone ice prepared in Example 1 and the ordinary ice that cannot release ozone prepared in Comparative Example 10 were mixed with water at a mass ratio of 1:5, and the litchi was precooled for 20 minutes. Then it was stored at 10°C for 11 days, and the total colony count, brightness, respiration rate, soluble solids and relative conductivity of the litchi were measured. The results are shown in Table 2.

[0092] Table 2

[0093]

[0094] As can be seen from Table 2, the total colony count, respiration rate and relative conductivity of the lychees treated with the micro-nano ozone ice of Example 1 decreased by 97.53%, 24.01% and 1.90% respectively compared with the comparative example 10, indicating that the ozone released by the micro-nano ozone ice prepared by the present invention has a significant disinfecting effect on the microorganisms on the surface of the lychees, the respiration of the fruit is significantly inhibited, and the integrity of the peel cells is better; the brightness L value and soluble solids of the lychees are increased by 1.94% and 2.31% respectively, indicating that the lychees pre-cooled with micro-nano ozone ice have brighter color, better taste, and significantly improved overall quality.

[0095] The above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing micro-nano ozone ice, characterized in that: include: Step A, using a venturi ejector to mix ozone and water at high speed to produce micro-nano ozone water; Step B, injecting the micro-nano ozone water into a salt solution at -20°C to -40°C to obtain micro-nano ozone ice; The salt solution is an aqueous solution containing NaCl and CaCl2.

2. The preparation method according to claim 1, characterized in that: In step A, the temperature of the water is 2-5° C., and the pH value is 7.0-9.

0.

3. The preparation method according to claim 1, characterized in that: In step A, the ozone is introduced for 10 to 15 minutes.

4. The preparation method according to claim 1, characterized in that: In step A, the pressure of the venturi ejector is 0.3-0.5 MPa.

5. The preparation method according to claim 1, characterized in that: In step B, The salt solution is an aqueous solution containing 20-30wt% NaCl and 20-30wt% CaCl2.

6. Micro-nano ozone ice prepared by the preparation method according to any one of claims 1 to 5.

7. The device for preparing the micro-nano ozone ice according to claim 6, characterized in that: include: Water storage tanks; a control unit connected to the water storage tank and controlling the generation of ozone and introducing the ozone into the water storage tank, and a micro-nano ozone ice generator connected to the water storage tank; The micro-nano ozone ice generator comprises: a quick cooling device containing a -20°C salt solution and a mold placed in the salt solution for molding the micro-nano ozone water.

8. The device according to claim 7, characterized in that The control unit comprises: an ozone generator and a venturi ejector; The venturi ejector is provided with a water inlet, an air inlet and an ozone water emission port; The control unit is connected to the water storage tank through the water inlet and the ozone water emission port of the venturi injector respectively.

9. The device according to claim 8, characterized in that The control unit further comprises a pressure gauge, a flow meter and a water pump 1 arranged between the water inlet of the venturi ejector and the water storage tank; A water pump 2 is also provided between the water storage tank and the micro-nano ozone ice reactor to pump the micro-nano ozone water in the water storage tank into the mold of the micro-nano ozone reactor.

10. Use of the micro-nano ozone ice according to claim 6, the micro-nano ozone ice prepared by the preparation method according to any one of claims 1 to 5, or the device according to any one of claims 7 to 9 in the preservation or storage of agricultural products.

11. A method for preserving agricultural products, characterized in that: include: Agricultural products are precooled using the micro-nano ozone ice described in claim 6, the micro-nano ozone ice prepared by the preparation method described in any one of claims 1 to 5, or the micro-nano ozone ice prepared by the device described in any one of claims 7 to 9.

12. The preservation method according to claim 8, characterized in that: The agricultural products include fruits and vegetables; The fruits include lychee, longan, rambutan and mangosteen; the vegetables include cowpea, green bean, bitter melon, cucumber and tomato.

13. The fresh-keeping method according to claim 8 or 9, wherein the precooling treatment comprises: The micro-nano ozone ice and water are mixed in a mass ratio of 1:(3-5) to obtain an ozone ice-water mixture; The agricultural products are added into the ozone-ice-water mixture and treated for 10 to 20 minutes.

14. The preservation method according to claim 8, characterized in that: The mass ratio of the agricultural product to the ozone ice-water mixture is 1:(3-10).

15. A method for precooling agricultural products, characterized in that: Before agricultural products are stored, they are processed as follows: Precooling agricultural products by using the micro-nano ozone ice described in claim 6, the micro-nano ozone ice prepared by the preparation method described in any one of claims 1 to 5, or the micro-nano ozone ice prepared by the device described in any one of claims 7 to 9, or The agricultural products are preserved by the preservation method described in any one of claims 8 to 11.

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