Aerogel fresh-keeping pad, preparation method thereof and application of aerogel fresh-keeping pad in fresh-keeping of fresh yellow pepper
By preparing anisotropic aerogel fresh-keeping pad, the problem of poor fresh-keeping effect of fresh-colored yellow tribute pepper is solved, the sustained release performance and good mechanical protection effect of the aerogel fresh-keeping pad is achieved, and the fresh-keeping effect and quality of the yellow tribute pepper is significantly improved.
Patent Information
- Application Number
- CN202510456761.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-12
- Publication Date
- 2025-05-30
AI Technical Summary
The prior art has poor effect in preserving fresh yellow tribute peppers, especially in large batches of bulk yellow tribute peppers, which are difficult to achieve.
By using the preparation method of an aerogel fresh-keeping pad, aerogel with sustained release properties is prepared by mixing sodium alginate solution with acetic acid, prefreezing and freeze-drying to form an anisotropic aerogel, and a copper-based metal organic frame is formed on its surface and essential oil soaking is carried out to prepare aerogel fresh-keeping pad with sustained release properties.
The aerogel fresh-keeping pad significantly improves the fresh-keeping effect of fresh yellow tribute pepper by slow-release Shancangzi essential oil, extends its storage period, and has good mechanical protection and low heat conductivity, improving the quality of yellow tribute pepper.
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Figure CN120059292A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of food technology, and particularly relates to an aerogel fresh-keeping pad, a preparation method thereof, and an application thereof in the fresh-keeping of fresh yellow Gongjiao peppers. Background Art
[0002] The fruits of yellow Gongjiao peppers are slender, with an outer skin like drum joints. After ripening, they are bright yellow, with a thin skin and thick flesh, a crispy taste, and a sweet and spicy flavor. They are an important auxiliary material for Hunan cuisine.
[0003] The market time of yellow Gongjiao peppers is relatively concentrated, and their production has seasonal and regional characteristics. There is a prominent contradiction between this and the annual consumption demand. There is a supply glut during the peak season and a supply shortage during the off-season. Therefore, it is extremely important to preserve and store peppers after harvesting to extend the supply period of fresh yellow Gongjiao peppers. Although there are currently methods for preserving yellow Gongjiao peppers, most of them involve deep processing and preservation of yellow Gongjiao peppers, such as processing them into dried yellow Gongjiao peppers or preparing pickled peppers, etc. There are few research reports on other methods for preserving and storing fresh yellow Gongjiao peppers. Currently, for the preservation of fresh peppers, the existing technologies mostly use methods such as modified atmosphere packaging and coating preservation, but the above methods are not applicable to the preservation of large quantities of bulk fresh yellow Gongjiao peppers after harvesting.
[0004] Refrigeration, that is, low-temperature preservation, is the most common method for post-harvest preservation of peppers. However, long-term production practice has found that simple refrigeration treatment is difficult to achieve an ideal preservation effect. Summary of the Invention
[0005] The purpose of this application is to provide an aerogel fresh-keeping pad, a preparation method thereof, and an application thereof in the fresh-keeping of fresh yellow Gongjiao peppers, which can solve the problems of poor preservation effect and inapplicability to the preservation of large quantities of yellow Gongjiao peppers existing in the existing preservation technologies.
[0006] To solve the above technical problems, this application is implemented as follows: In a first aspect, this application provides a preparation method for an aerogel fresh-keeping pad, including the following steps: Mix sodium alginate solution with acetic acid to obtain a mixed solution; Perform unidirectional freezing pre-freezing treatment and freeze-drying treatment on the mixed solution in sequence according to unidirectional freezing pre-freezing parameters and freeze-drying parameters to obtain an anisotropic aerogel; Use the in-situ growth method to prepare a metal-organic framework on the surface of the aerogel, and then obtain an anisotropic aerogel fresh-keeping pad through essential oil soaking treatment.
[0007] Further, based on the mass of the mixed solution being 100%, the mass concentration of sodium alginate is 1% - 2%; the mass concentration of acetic acid is 0.001% - 0.005%.
[0008] Further, based on the total mass of the mixed solution being 100%, the mass concentration of sodium alginate is 2%; the mass concentration of acetic acid is 0.002%.
[0009] Further, the unidirectional freezing pre-freezing parameters include: the pre-freezing temperature is -75~-85°C, and the pre-freezing time is 11~13 h; The freeze-drying parameters include: the drying temperature is -45~-55°C, the drying time is 45~50 h, and the vacuum pressure is 18~22 Pa.
[0010] Further still, the unidirectional freezing pre-freezing parameters include: the pre-freezing temperature is -80°C, and the pre-freezing time is 12 h; The freeze-drying parameters include: the drying temperature is -50°C, the drying time is 48 h, and the vacuum pressure is 20 Pa.
[0011] Further, the metal-organic framework is a copper-based metal-organic framework; The steps of preparing the metal-organic framework on the surface of the aerogel by the in-situ growth method specifically include: Soaking the aerogel in a copper nitrate solution with a concentration of 10 mg / mL~30 mg / mL for 11~13 h, and then performing a hydrothermal reaction in a benzenetricarboxylic acid ethanol solution with a concentration of 10 mg / mL~30 mg / mL according to the hydrothermal reaction parameters to prepare a copper-based metal-organic framework on the surface of the aerogel; Among them, the hydrothermal reaction parameters include: the reaction time is 23~25 h, and the reaction temperature is 80~90°C.
[0012] Further still, the metal-organic framework is a copper-based metal-organic framework; The steps of preparing the metal-organic framework on the surface of the aerogel by the in-situ growth method specifically include: Soaking the aerogel in a copper nitrate solution with a concentration of 30 mg / mL for 12 h, and then performing a hydrothermal reaction in a benzenetricarboxylic acid ethanol solution with a concentration of 20 mg / mL according to the hydrothermal reaction parameters to prepare a copper-based metal-organic framework on the surface of the aerogel; Among them, the hydrothermal reaction parameters include: the reaction time is 24 h, and the reaction temperature is 90°C.
[0013] Further, the essential oil soaking treatment includes: soaking in a mixed solution of litsea cubeba essential oil and absolute ethanol with a volume ratio of 2:3~4:1 for 23~25 h.
[0014] Further still, the essential oil soaking treatment includes: soaking in a mixed solution of litsea cubeba essential oil and absolute ethanol with a volume ratio of 4:1 for 24 h.
[0015] In a second aspect, the present application provides an aerogel fresh-keeping pad, which is prepared by the above-mentioned preparation method of the aerogel fresh-keeping pad.
[0016] In a third aspect, the present application provides an application of an aerogel fresh-keeping pad in the fresh-keeping of fresh yellow Gongjiao peppers, including the following steps: Pre-treat the fresh yellow Gongjiao peppers to obtain pre-treated fresh yellow Gongjiao peppers; Arrange the aerogel fresh-keeping pads at multiple positions inside the storage container to surround the pre-treated fresh yellow Gongjiao peppers, and then carry out low-temperature storage.
[0017] Furthermore, the pre-treatment includes sorting, drying, and pre-cooling treatments; Among them, the pre-cooling treatment is used to reduce the surface temperature of the fresh yellow Gongjiao peppers to 7 - 12°C.
[0018] Furthermore, the step of arranging the aerogel fresh-keeping pads at multiple positions inside the storage container to surround the pre-treated fresh yellow Gongjiao peppers and then carrying out low-temperature storage specifically includes: Arrange the aerogel fresh-keeping pads at the bottom, around the sides, and on the top of the storage container to completely surround the pre-treated fresh yellow Gongjiao peppers, and then carry out low-temperature storage.
[0019] Furthermore, the temperature of the low-temperature storage is 7 - 12°C.
[0020] Even further, the temperature of the low-temperature storage is 12°C.
[0021] Compared with the prior art, the present application has at least one of the following beneficial effects: (1) In the preparation method of the aerogel fresh-keeping pad proposed in the present application, by selecting the natural plant extract litsea cubeba essential oil as the active ingredient and using the in-situ generation method to generate a metal-organic framework on the surface of the anisotropic aerogel fresh-keeping pad and encapsulate the plant essential oil, the problems of low water solubility and high volatility of the plant essential oil can be solved, thus bringing a better fresh-keeping effect.
[0022] (2) The aerogel fresh-keeping pad prepared in the present application is a slow-release fresh-keeping pad. Compared with the traditional fresh-keeping method that only relies on plant essential oil, the aerogel fresh-keeping pad of the present application combines the excellent characteristics of plant essential oil, anisotropic aerogel, and metal-organic framework, has good slow-release performance, can continuously and slowly release the essential oil components in the environment, and act on the surface of fresh yellow Gongjiao peppers for a long time to achieve the effect of long-term fresh-keeping.
[0023] (3) The anisotropic aerogel fresh-keeping pad prepared in the present application has a resilient property and an extremely low thermal conductivity. From the physical protection level, it can effectively reduce the risk of mechanical damage, stabilize the microenvironment temperature in the environmental dimension, thereby enhancing the adaptability of yellow Gongjiao peppers to the environment during storage. The combination of low temperature and litsea cubeba essential oil aerogel fresh-keeping pad has a good synergistic effect and achieves a good fresh-keeping effect. Moreover, the preparation method is simple to operate, green and environmentally friendly, effectively improves the action time of the essential oil, and significantly improves the quality of fresh yellow Gongjiao peppers. Description of the Drawings Figure 1 It is a physical picture of fresh Huanggong peppers on the 0th, 10th, 20th, 30th, and 40th days of storage in Example 1 and Comparative Examples 1-4. Detailed Embodiment
[0024] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.
[0025] The present application provides a preparation method of an aerogel fresh-keeping pad and its application in the fresh-keeping of fresh Huanggong peppers. The steps are as follows: (1) Pretreatment of fresh Huanggong peppers: Select, dry, and precool the freshly picked fresh Huanggong peppers. (2) Preparation of aerogel: Mix sodium alginate solution and acetic acid, pour the mixed solution into a mold for unidirectional freezing pretreatment, and then perform freeze-drying treatment to obtain an anisotropic aerogel.
[0026] (3) Preparation of the aerogel fresh-keeping pad: Use the in-situ generation method to generate a copper-based metal-organic framework on the surface of the aerogel obtained in step (2), and then perform essential oil soaking treatment to obtain an anisotropic aerogel fresh-keeping pad.
[0027] (4) Fresh-keeping treatment: Place the fresh-keeping pads prepared in step (3) at the bottom and around the carton, place the fresh Huanggong peppers processed in step (1) in the middle of the carton, and place the aerogel fresh-keeping pads on the top, and combine low-temperature storage to perform fresh-keeping treatment on the fresh Huanggong peppers.
[0028] In some embodiments of the present application, in the pretreatment of step (1), the selection criteria are Huanggong peppers with plump and complete fruits, thick and firm pulp, golden and shiny skin color, appropriate maturity, no pests and diseases, and no mechanical damage. Inferior fruits and diseased fruits are removed. The criteria for drying and precooling treatment are to stack the Huanggong peppers in a dry room for natural air-drying, and precool the Huanggong peppers in a cold storage at 20-25°C. After the Huanggong peppers are cooled to 20-25°C, adjust the temperature of the cold storage to 7-12°C to make the temperature of the Huanggong peppers drop to 7-12°C.
[0029] In some embodiments of the present application, based on the mass of the mixed solution being 100%, the mass concentration of sodium alginate is 1.00% - 2.00%; the mass concentration of acetic acid is 0.001% - 0.005%, the pre-freezing temperature of the unidirectional freezing pre-freezing treatment is -75 to -85 °C, the pre-freezing time is 11 - 13 h, the drying temperature of the freeze-drying is -45 to -55 °C, the drying time is 45 - 50 h, and the vacuum pressure is 18 - 22 Pa.
[0030] It should be noted that the sodium alginate molecular chain selected in the present application is rich in carboxyl groups (~COO⁻), and forms a stable sol through hydrogen bonds and electrostatic repulsion in the solution. When acetic acid (weak acid) is added, the pH of the solution decreases, the carboxyl groups are converted into neutral carboxylic acids (~COOH), the hydrophilicity of the molecular chain decreases, triggering the hydrophobic association effect, promoting the cross-linking of sodium alginate with copper ions to form a three-dimensional network gel.
[0031] Among them, the specific operation and principle of forming anisotropic aerogel during the unidirectional freezing pre-freezing treatment is that when the mixed solution is poured into a mold placed on a copper plate, the copper plate contacts with ethanol (-80 °C) to form a temperature gradient from bottom to top. Due to the temperature gradient from bottom to top, heat is unidirectionally conducted, resulting in the unidirectional growth and expansion of the ice region during freezing. The ice peaks squeeze the sodium alginate sol into the ice crystal gaps, forming a layered / honeycomb structure of the sodium alginate sol. During further freeze-drying, the ice sublimes and fills with gas, which preserves the layered / honeycomb skeleton, making the aerogel anisotropic. The unidirectional freezing pre-freezing forms directionally arranged ice crystals, and anisotropic aerogel is obtained after freeze-drying.
[0032] In some embodiments of the present application, the in-situ generation method for preparing copper-based metal-organic frameworks in step (3) means soaking in a copper nitrate solution with a concentration of 10 mg / ml - 30 mg / ml for 11 - 13 hours; then hydrothermal reacting in a benzene tricarboxylic acid ethanol solution with a concentration of 10 mg / ml - 30 mg / ml for 23 - 25 hours, where the reaction temperature is 80 - 90 °C; the essential oil soaking treatment is soaking in a mixed solution of Litsea cubeba essential oil and absolute ethanol with a volume ratio of 2:3 - 4:1.
[0033] It should be noted that using natural plant extract Litsea cubeba essential oil as the active ingredient, using sodium alginate and acetic acid as the aerogel fresh-keeping pad, and metal-organic frameworks as the essential oil carrier, through adjusting the ratio, loading Litsea cubeba essential oil in the carrier, making Litsea cubeba essential oil slowly release and act on fresh Huanggong peppers, and combining with low-temperature storage to extend its fresh-keeping time limit, can effectively improve the quality of fresh Huanggong peppers during storage.
[0034] In some embodiments of the present application, the temperature of the low-temperature storage in step (4) is 7 - 12 °C.
[0035] It should be noted that although single low-temperature storage has a certain fresh-keeping effect, it is not sufficient to resist the microbial infection suffered by fresh Huang Gongjiao peppers. The anisotropic aerogel fresh-keeping pad prepared in this application selects sodium alginate aerogel containing metal-organic framework as the carrier of Litsea cubeba essential oil, which can not only solve the problems of low water solubility and easy volatility of Litsea cubeba essential oil, but also the aerogel fresh-keeping pad has good heat preservation performance and buffering performance, and is not easily affected by various external environmental factors such as temperature and mechanical damage during storage and transportation. At the same time, this invention selects low temperature combined with Litsea cubeba essential oil aerogel fresh-keeping pad, which has a good synergistic effect and achieves a good fresh-keeping effect.
[0036] The following uses specific embodiments to further illustrate the present invention in detail, but this application is not limited to the following specific embodiments.
[0037] Example 1 (1) Pretreatment of fresh Huang Gongjiao peppers: Select, dry, and precool the freshly picked fresh Huang Gongjiao peppers; the selection criteria are Huang Gongjiao peppers with plump and complete fruits, thick and firm pulp, golden and shiny skin color, appropriate maturity, and no pests, diseases, and mechanical damage. Discard inferior fruits, diseased fruits, etc. The drying and precooling treatment standards are to stack the Huang Gongjiao peppers in a dry room for natural air drying, precool the Huang Gongjiao peppers in a cold storage at 20°C. After the Huang Gongjiao peppers are cooled to 20°C, adjust the cold storage temperature to 12°C to make the Huang Gongjiao peppers cool to 12°C.
[0038] (2) Preparation of aerogel: Mix sodium alginate solution and acetic acid, pour the mixed solution into a mold for unidirectional freezing and precooling, and obtain anisotropic aerogel after freeze-drying. Based on the mass of the mixed solution being 100%, the mass concentration of sodium alginate is 2.00%; the mass concentration of acetic acid is 0.002%; the precooling temperature is -80°C, and the precooling time is 12 h; The freeze-drying temperature is -50°C, the freeze-drying time is 48 h, and the vacuum pressure is 20 Pa.
[0039] (3) Preparation of aerogel fresh-keeping pad: Use the in-situ generation method to generate copper-based metal-organic framework on the surface of the aerogel obtained in step (2), and then soak it with essential oil to obtain an anisotropic aerogel fresh-keeping pad. The copper-based metal-organic framework obtained means soaking in a copper nitrate solution with a concentration of 30 mg / mL for 12 hours; the hydrothermal reaction time in a benzenetricarboxylic acid ethanol solution with a concentration of 20 mg / mL is 24 hours, where the reaction temperature is 90°C; in the essential oil soaking, the volume ratio of Litsea cubeba essential oil to absolute ethanol is 4:1.
[0040] (4) Fresh-keeping treatment: Place the aerogel fresh-keeping pads at the bottom and around the cardboard box with the fresh-keeping pads prepared in step (3). Place the fresh Huanggong peppers treated in step (1) in the middle of the cardboard box, and place an aerogel fresh-keeping pad on the top. Combine low-temperature storage to conduct fresh-keeping treatment on the fresh Huanggong peppers. Low-temperature storage means adjusting the temperature of the cold storage to 12°C.
[0041] Example 2 Example 2 is basically the same as Example 1, except that: In step (3), the ratio of fructus viticis essential oil to absolute ethanol is 3:2.
[0042] Example 3 Example 3 is basically the same as Example 1, except that: In step (3), the ratio of fructus viticis essential oil to absolute ethanol is 2:3.
[0043] Comparative Example 1 The preparation method for fresh-keeping of fresh Huanggong peppers in this example includes the following steps: (1) Select Huanggong peppers with plump and complete fruits, thick and firm pulp, golden-yellow and shiny skin color, appropriate maturity, and no diseases, pests and mechanical damage. Remove inferior fruits, diseased fruits, etc., and put them into a cardboard box after drying and pre-cooling. (2) Directly conduct low-temperature storage on the fresh Huanggong peppers (the specific conditions for low-temperature storage are: adjust the temperature of the cold storage to 12°C).
[0044] Comparative Example 2 The preparation method for fresh-keeping of fresh Huanggong peppers in this example includes the following steps: (1) Select Huanggong peppers with plump and complete fruits, thick and firm pulp, golden-yellow and shiny skin color, appropriate maturity, and no diseases, pests and mechanical damage. Remove inferior fruits, diseased fruits, etc., and put them into a cardboard box after drying and pre-cooling. (2) Mix sodium alginate, acetic acid and water and conduct unidirectional freezing with a mold, and then freeze-dry for 48 hours to obtain an aerogel. Among them: based on the mass of the mixed solution being 100%, the mass concentration of sodium alginate is 2.00%, and the mass concentration of acetic acid is 0.002%. (3) Put the aerogel prepared in step (2) into a cardboard box, and apply it to fresh Huanggong peppers in combination with low-temperature storage (the specific conditions for low-temperature storage are: adjust the temperature of the cold storage to 12°C).
[0045] Comparative Example 3 The preparation method for fresh-keeping of fresh Huanggong peppers in this example includes the following steps: (1) Select Huanggong peppers with plump and complete fruits, thick and firm pulp, golden-yellow and shiny skin color, appropriate maturity, and no diseases, pests and mechanical damage. Remove inferior fruits, diseased fruits, etc., and put them into a cardboard box after drying and pre-cooling. (2) Preparation of aerogel: Mix the sodium alginate solution and acetic acid solution, pour the mixed solution into a mold and freeze it, and obtain the aerogel after freeze-drying after pre-freezing; wherein: based on the mass of the mixed solution being 100%, the mass concentration of sodium alginate is 2.00%, and the mass concentration of acetic acid is 0.002%; (3) Preparation of aerogel fresh-keeping pad: Immerse the aerogel obtained in step (2) in a mixed solution of litsea cubeba essential oil and absolute ethanol, and finally dry it with cold air; wherein: the ratio of litsea cubeba essential oil to absolute ethanol is 4:1; (4) Fresh-keeping treatment: Place the fresh-keeping pads prepared in step (3) at the bottom and around the carton, place the fresh Huang Gong peppers treated in step (1) in the middle of the carton, and place fresh-keeping pads at the top, and combine low-temperature storage to carry out fresh-keeping treatment on fresh Huang Gong peppers.
[0046] Comparative Example 4 The preparation method for preserving fresh Huang Gong peppers in this example includes the following steps: (1) Select Huang Gong peppers with plump and complete fruits, thick and firm pulp, golden yellow and shiny skin color, appropriate maturity, no diseases and pests, and no mechanical damage, remove inferior fruits, diseased fruits, etc., and put them into a carton after drying and pre-cooling; (2) Weigh 0.3 g of litsea cubeba essential oil and add it to the carton; (3) Store the treated fresh Huang Gong peppers at a low temperature (the specific conditions for low-temperature storage are: adjust the cold storage temperature to 12°C).
[0047] Next, the effects of the examples and comparative examples of the present invention are tested.
[0048] Using the fresh-keeping methods of Huang Gong peppers in Examples 1-3 and Comparative Examples 1-4, select 55 g of plump, complete, and golden yellow and shiny Huang Gong peppers in each group for treatment, and observe the fresh-keeping effects of Huang Gong peppers within 40 days of storage respectively.
[0049] The results are as Figure 1 shown. Through analysis, the following conclusions can be obtained: Compared with Comparative Examples 1, 2, 3, and 4, Examples 1, 2, and 3 have better fresh-keeping effects on Huang Gong peppers, delaying the reproduction of pathogenic microorganisms and the softening of Huang Gong peppers.
[0050] Compared with Example 1, Comparative Example 1 only performs low-temperature treatment, indicating that low-temperature treatment has a certain fresh-keeping effect but is not as good as the fresh-keeping pad of the essential oil aerogel rich in metal-organic frameworks in this application.
[0051] Compared with Example 1, no litsea cubeba essential oil is added in Comparative Example 2, indicating that plant essential oils have good fresh-keeping effects and significantly reduce the degree of quality decline during the storage of Huang Gong peppers.
[0052] Compared with Example 1, the aerogel prepared in Comparative Example 3 did not generate metal-organic frameworks. From the comparison results of the photos, it can be seen that the fresh-keeping effect of the yellow Gongjiao preserved by the aerogel containing metal-organic frameworks is better, because the essential oil aerogel fresh-keeping pad rich in metal-organic frameworks prepared by the reaction can increase the content of essential oil loaded in the aerogel, delay the release of the essential oil, and improve its action time limit.
[0053] Compared with Example 1, in Comparative Example 4, low temperature was combined with Litsea cubeba essential oil, and the fresh-keeping effect was quite different from that of Example 1. This shows that during storage, the essential oil aerogel fresh-keeping pad rich in metal-organic frameworks delays the release of the essential oil, improves its action time limit, and can better maintain the quality of yellow Gongjiao.
[0054] In the examples, Litsea cubeba essential oils with different concentration ratios were selected. During the experiment, it was found that when the ratio of Litsea cubeba essential oil to absolute ethanol was 4:1 in Examples 1, 2, and 3, and combined with low temperature, the fresh-keeping effect on yellow Gongjiao was the best. The comprehensive results showed that the effect of Example 1 was the best, maximizing the preservation of the quality of yellow Gongjiao.
[0055] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all of them belong to the protection scope of the present application.
Claims
1. A method for preparing an aerogel fresh-keeping pad, characterized in that: The following steps are involved: mixing the sodium alginate solution with acetic acid to obtain a mixed solution; According to the unidirectional freezing pre-freezing parameters and the freeze-drying parameters, the mixed solution is subjected to unidirectional freezing pre-freezing treatment and freeze-drying treatment in sequence to obtain an anisotropic aerogel; A metal organic framework is prepared on the surface of the aerogel by an in-situ growth method, and then an anisotropic aerogel fresh-keeping pad is obtained by soaking in essential oil.
2. The preparation method according to claim 1, characterized in that: Taking the mass of the mixed solution as 100%, The mass concentration of the sodium alginate is 1% to 2%; The mass concentration of the acetic acid is 0.001% to 0.005%.
3. The preparation method according to claim 1, characterized in that: The one-way freezing pre-freezing parameters include: pre-freezing temperature of -75~-85°C, pre-freezing time of 11~13h; The freeze-drying parameters include: drying temperature of -45 to -55°C, drying time of 45 to 50 hours, and vacuum pressure of 18 to 22 Pa.
4. The preparation method according to claim 1, characterized in that: The metal organic framework is a copper-based metal organic framework; The steps of preparing a metal organic framework on the surface of the aerogel by an in-situ growth method specifically include: The aerogel is immersed in a copper nitrate solution with a concentration of 10 mg / mL to 30 mg / mL for 11 to 13 hours, and then subjected to a hydrothermal reaction in a benzenetricarboxylic acid ethanol solution with a concentration of 10 mg / mL to 30 mg / mL according to a hydrothermal reaction parameter, so as to prepare a copper-based metal organic framework on the surface of the aerogel; Wherein, the hydrothermal reaction parameters include: reaction time is 23~25h, reaction temperature is 80~90℃.
5. The preparation method according to claim 1, characterized in that: The essential oil soaking process comprises: Soak in a mixed solution of Litsea cubeba essential oil and anhydrous ethanol in a volume ratio of 2:3~4:1 for 23~25 h.
6. An aerogel fresh-keeping pad, characterized in that: The aerogel fresh-keeping pad is prepared by the preparation method of any one of claims 1 to 5.
7. An application of the aerogel fresh-keeping pad as claimed in claim 6 in preserving fresh yellow pepper, characterized in that: The following steps are involved: Pre-treating the fresh yellow pepper to obtain the pre-treated fresh yellow pepper; The aerogel fresh-keeping pads are arranged at multiple positions inside the storage container to surround the pretreated fresh yellow peppers, and then the fresh peppers are stored at low temperatures.
8. The use according to claim 7, characterized in that: The pretreatment includes selection, drying and precooling; Wherein, the pre-cooling treatment is used to reduce the surface temperature of fresh yellow pepper to 7-12°C.
9. The use according to claim 7, characterized in that: The step of arranging the aerogel fresh-keeping pads at multiple positions inside the storage container to surround the pretreated fresh yellow pepper and then performing low-temperature storage specifically includes: The aerogel fresh-keeping mat is arranged at the bottom, around and top of the storage container to fully surround the pretreated fresh yellow pepper, and then the fresh pepper is stored at a low temperature.
10. The use according to claim 9, characterized in that: The low temperature storage temperature is 7-12°C.