A sustained-release bacteriostatic gel system and its preparation method and application

Abstract

This invention provides a sustained-release antibacterial gel system, its preparation method, and its application. The preparation method includes the following steps: 1) preparing a salicylaldehyde-loaded sustained-release gel sheet through acylation, neutralization, and covalent grafting; 2) mixing the loaded salicylaldehyde sustained-release gel sheet with a promoter citrate-disodium hydrogen phosphate buffer solution, and supplementing with 2-methylbutyric acid to obtain the sustained-release antibacterial gel system. The sustained-release antibacterial gel system produced by this invention can effectively inhibit and kill the soft rot pathogen *Rhizopus stolonifer*, improve the resistance of agricultural products, and extend the storage period of agricultural products. The preparation process provided by this invention is simple, green, safe, and easy for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agricultural product storage, in particular to a slow-release bacteriostatic gel system, a preparation method and application thereof. BACKGROUND

[0002] Sweet potato (Ipomoea batatas [L] Lam) is a globally recognized nutritious food with rich nutritional value and contains various bioactive components. However, due to the large specific surface area and high water content of sweet potato tubers, they are prone to microbial rot, weight loss and tissue softening during storage, thus the storage time is limited. Generally, the factors affecting the postharvest quality of sweet potatoes are divided into internal factors and external factors. Among the internal factors, weight loss is the main factor reflecting the aging of sweet potatoes, which mainly affects the metabolic activities related to quality deterioration such as softening and browning. Microbial spoilage is the main external factor leading to rapid deterioration of sweet potatoes after storage.

[0003] Rhizopus soft rot is a serious postharvest disease of sweet potatoes caused by Rhizopus stolonifer. Rhizopus stolonifer not only infects sweet potatoes, but also invades other annual and perennial plants. Therefore, this devastating disease reduces the yield and quality of crops worldwide. Generally, the pathogen infects agricultural products through wounds during postharvest storage and transportation. When sweet potatoes are infected with Rhizopus stolonifer, they produce toxic ipomeanol. This phenomenon is considered a potential economic problem and health risk. In recent years, synthetic fungicides are still the main means to control this microorganism, but synthetic fungicides can cause environmental pollution and increase the resistance of postharvest pathogens. Therefore, there is an urgent need for safe and environmentally friendly preservation methods.

[0004] Based on the above problems, the research on green and safe preservation methods has become a hot research direction in the field of postharvest preservation of agricultural products in recent years. Currently, there are slow-release microcapsule preservatives prepared by using chitosan and sodium alginate as raw materials, adding cinnamon essential oil, thyme essential oil and oregano essential oil (CN101506061A), and fruit and vegetable preservatives prepared from Artemisia leaf extract (CN107212073A), but such preservatives are mainly used for fresh-cut fruit and vegetable preservation, with a short preservation period of only 3-4 days. There is no good preservation method for long-term storage and preservation of agricultural products such as sweet potatoes. In addition, some preservatives such as salicylic acid and / or p-hydroxybenzoic acid preparation for preventing and / or treating bacterial soft rot (CN114145300A) are mainly aimed at bacterial soft rot, and there is no good solution for fungal soft rot caused by Rhizopus stolonifer.

[0005] Therefore, how to provide a green and safe bacteriostatic system to effectively inhibit the growth of pathogenic microorganisms of agricultural products, so as to achieve the purpose of effective preservation and extension of storage period of agricultural products is still a problem to be solved by those skilled in the art. SUMMARY

[0006] To solve the above technical problems, the present application provides a sustained-release bacteriostatic gel system and a preparation method thereof.

[0007] Specifically, the preparation method of the sustained-release bacteriostatic gel system provided by the first aspect of the present application comprises the following steps:

[0008] 1) preparing a salicylaldehyde-loaded sustained-release gel sheet by acylation, neutralization and covalent grafting;

[0009] 2) mixing the salicylaldehyde-loaded sustained-release gel sheet with a promoter of citric acid-disodium hydrogen phosphate buffer solution, and adding 2-methylbutyric acid to obtain the sustained-release bacteriostatic gel system.

[0010] The present application finds that, by using the salicylaldehyde-loaded sustained-release gel sheet as the matrix, the citric acid-disodium hydrogen phosphate buffer solution as the promoter, and the 2-methylbutyric acid as the auxiliary, not only the slow release of salicylaldehyde can be achieved, but also the synergistic bacteriostatic effect of salicylaldehyde and 2-methylbutyric acid can be achieved, thereby effectively inhibiting the growth of Rhizopus stolonifer and significantly prolonging the storage period of agricultural products.

[0011] Specifically, in step 1), the acylation comprises uniformly mixing chitosan, organic acid and water in a mass ratio of 3:1:100-300, stirring at 40-60℃ for 0.2-2.0h, and drying at 30-45℃ and 30%-45% relative humidity for 12-60h to obtain the acylated chitosan gel sheet.

[0012] As a preferred, in step 1), the acylation comprises uniformly mixing chitosan, organic acid and water in a mass ratio of 3:1:150-250, stirring at 45-55℃ for 0.5-1.5h, and drying at 35-40℃ and 30%-40% relative humidity for 12-50h to obtain the acylated chitosan gel sheet.

[0013] Further preferably, in step 1), the acylation comprises uniformly mixing chitosan, organic acid and water in a mass ratio of 3:1:180-220, stirring at 50℃ for 1h, and drying at 37℃ and 40% relative humidity for 48h to obtain the acylated chitosan gel sheet.

[0014] Specifically, in step 1), the organic acid is selected from one or more of acetic acid, formic acid and citric acid, and is preferably acetic acid.

[0015] Specifically, in step 1), the neutralization comprises immersing the acylated chitosan gel sheet in a 0.05-0.2M sodium hydroxide aqueous solution for 12-48h, and drying at 30-45℃ and 30%-45% relative humidity for 12-30h to obtain the neutralized chitosan gel sheet.

[0016] As preferred, in step 1), the neutralization is: immersing the acylated chitosan gel piece into 0.05-0.15M aqueous sodium hydroxide solution for 12-30h, drying at 35-40℃, 30%-40% relative humidity for 12-30h, to obtain the neutralized chitosan gel piece.

[0017] Further preferably, in step 1), the neutralization is: immersing the acylated chitosan gel piece into 0.08-0.12M aqueous sodium hydroxide solution for 24h, drying at 37℃, 40% relative humidity for 24h, to obtain the neutralized chitosan gel piece.

[0018] Specifically, in step 1), the covalent grafting comprises mixing the neutralized chitosan gel piece, salicylaldehyde, and an alcoholic solvent in a mass ratio of 1:1-10:50-100, and oscillating at 50-70℃ for 15-40h, to obtain the salicylaldehyde-loaded sustained-release gel piece.

[0019] As preferred, in step 1), the covalent grafting is: mixing the neutralized chitosan gel piece, salicylaldehyde, and an alcoholic solvent in a mass ratio of 1:2-8:60-90, and oscillating at 55-65℃ for 18-30h, to obtain the salicylaldehyde-loaded sustained-release gel piece.

[0020] Further preferably, in step 1), the covalent grafting is: mixing the neutralized chitosan gel piece, salicylaldehyde, and an alcoholic solvent in a mass ratio of 1:3-5:70-80, and oscillating at 60℃ for 24h, to obtain the salicylaldehyde-loaded sustained-release gel piece.

[0021] Specifically, in step 1), the alcoholic solvent is selected from one or more of ethanol, propylene glycol, glycerol, n-propanol, isopropanol, n-butanol, n-pentanol, and isoamyl alcohol, and is preferably ethanol.

[0022] Specifically, in step 2), the molar concentration of the citric acid-disodium hydrogen phosphate buffer is 0.1-0.2mol / L, the pH value is 3-7, and the mass ratio of the citric acid-disodium hydrogen phosphate buffer to the salicylaldehyde-loaded sustained-release gel piece is 1-8:1.

[0023] As preferred, in step 2), the molar concentration of the citric acid-disodium hydrogen phosphate buffer is 0.1-0.2mol / L, the pH value is 3-5, and the mass ratio of the citric acid-disodium hydrogen phosphate buffer to the salicylaldehyde-loaded sustained-release gel piece is 1-5:1.

[0024] Further preferably, in step 2), the molar concentration of the citric acid-disodium hydrogen phosphate buffer is 0.1-0.2mol / L, the pH value is 4, and the mass ratio of the citric acid-disodium hydrogen phosphate buffer to the salicylaldehyde-loaded sustained-release gel piece is 2:1.

[0025] Specifically, in step 2), the mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet is 5-40:1, preferably 20:1.

[0026] Secondly, the present invention provides a sustained-release antibacterial gel system obtained by any of the above-mentioned methods for preparing sustained-release antibacterial gel systems.

[0027] Thirdly, the present invention provides the application of the above-mentioned sustained-release antibacterial gel system in the preservation of agricultural products.

[0028] In this invention, the slow-release antibacterial gel system is preferably used for the preservation of agricultural products, such as sweet potatoes and potatoes, but is not limited to these.

[0029] The slow-release antibacterial gel system described in this invention can simultaneously inhibit bacterial and fungal microbial diseases of agricultural products, and is particularly effective in controlling sweet potato soft rot caused by Rhizopus stolonifera.

[0030] The beneficial effects of this invention are at least as follows:

[0031] (1) The sustained-release antibacterial gel system and its preparation method provided by the present invention are simple to operate, easy to use, and easy to scale up and promote industrialization.

[0032] (2) The sustained-release antibacterial gel system provided by the present invention has a good antibacterial effect. Salicylic aldehyde has a strong antibacterial effect even in trace amounts. When salicylic aldehyde is used in combination with 2-methylbutyric acid, it has a significant synergistic antibacterial effect and is environmentally friendly and safe.

[0033] (3) The antibacterial components in the slow-release antibacterial gel system provided by the present invention can be slowly released during the storage of agricultural products. Only a small amount of antibacterial components are needed to achieve a stable and long-lasting antibacterial effect, which can meet the needs of long-term storage of agricultural products. At the same time, the slow-release antibacterial gel provided by the present invention does not come into direct contact with agricultural products, thus improving consumer safety.

[0034] (4) The slow-release antibacterial gel system provided by this invention can maintain the hardness of agricultural products during storage, reduce the germination rate, protect the integrity of cell walls, and increase the activity of phenylalanine ammonia-lyase and superoxide dismutase. While maintaining the quality of agricultural products, it can effectively inhibit the growth of Rhizopus stolonifer, the pathogen of soft rot, and significantly reduce the incidence of soft rot. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 These are comparative photographs of the sustained-release gel tablets of Example 2 and Comparative Example 1 of the present invention. Detailed Implementation

[0037] To clearly illustrate the content of this invention, a detailed description will be provided below. The following embodiments and comparative examples are used to illustrate the invention, but are not intended to limit its scope. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below.

[0038] Unless otherwise specified, specific techniques or conditions in the embodiments shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. The implementation conditions in the embodiments may be further adjusted according to specific experimental or factory conditions. Unspecified implementation conditions are generally those used in routine experiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and all raw materials used are commercially available products.

[0039] Unless otherwise specified, the percentage sign "%" used in this invention refers to volume percentage.

[0040] The microorganism involved in the examples, Rhizopus cremastogyne (CICC40327), is a pathogen that causes sweet potato soft rot and was obtained from the China Industrial Microbial Culture Collection Center.

[0041] The culture media involved in the examples, namely potato dextrose agar (PDA) medium and potato dextrose broth (PDB) medium, were obtained from Beijing Aoboxing Biotechnology Co., Ltd.

[0042] The sweet potatoes used in this example were "Pushu 32" sweet potatoes purchased from a local farm in Beijing. Fruits free from pests and diseases, mechanical damage, similar size, and uniform maturity were selected.

[0043] Example 1: Preparation of a sustained-release antibacterial gel system

[0044] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:200, stirred at 50°C for 1.0 h, and dried at 37°C and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in 0.1M sodium hydroxide aqueous solution for 24 h to neutralize, and dried at 37°C and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and alcohol solvents were mixed at a mass ratio of 1:2:60 and shaken at 60°C for 24 h to obtain covalently grafted loaded salicylaldehyde sustained-release gel sheets. Add the promoter citrate-disodium hydrogen phosphate buffer (molar concentration of 0.1-0.2 mol / L, pH value of 4, and mass ratio of 2:1 to the loaded salicylaldehyde sustained-release gel tablet), and supplement with 2-methylbutyric acid (mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet of 20:1) to obtain the sustained-release antibacterial gel system.

[0045] Example 2: Preparation of a sustained-release antibacterial gel system

[0046] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:210, stirred at 45°C for 2.0 h, and dried at 37°C and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in a 0.13M sodium hydroxide aqueous solution for 24 h to neutralize, and dried at 37°C and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and an alcohol solvent were mixed at a mass ratio of 1:3:60 and shaken at 60°C for 24 h to obtain covalently grafted loaded salicylaldehyde sustained-release gel sheets (see...). Figure 1 A). Add promoter citrate-disodium hydrogen phosphate buffer (molar concentration of 0.1-0.2 mol / L, pH value of 4, and mass ratio of 2:1 to the loaded salicylaldehyde sustained-release gel tablet), and supplement with 2-methylbutyric acid (mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet of 20:1) to obtain the sustained-release antibacterial gel system.

[0047] Example 3: Preparation of a sustained-release antibacterial gel system

[0048] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:250, stirred at 50℃ for 1.5 h, and dried at 37℃ and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then neutralized by immersing in a 0.12M sodium hydroxide aqueous solution for 20 h and dried at 37℃ and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and an alcohol solvent were mixed at a mass ratio of 1:4:60 and shaken at 55℃ for 36 h to obtain covalently grafted salicylaldehyde sustained-release gel sheets. A promoter citrate-disodium hydrogen phosphate buffer (molar concentration 0.1-0.2 mol / L, pH 4, mass ratio to loaded salicylaldehyde sustained-release gel sheets 2:1) was added, supplemented with 2-methylbutyric acid (20:1), to obtain the sustained-release antibacterial gel system.

[0049] Example 4: Preparation of a sustained-release antibacterial gel system

[0050] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:180, stirred at 55℃ for 1.0 h, and dried at 37℃ and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then neutralized by immersing in 0.08M sodium hydroxide aqueous solution for 36 h and dried at 37℃ and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and alcohol solvent were mixed at a mass ratio of 1:3:60 and shaken at 60℃ for 24 h to obtain covalently grafted salicylaldehyde sustained-release gel sheets. A promoter citrate-disodium hydrogen phosphate buffer (molar concentration 0.1-0.2 mol / L, pH 4, mass ratio of promoter to salicylaldehyde sustained-release gel sheet 4:1) was added, along with 2-methylbutyric acid (20:1), to obtain the sustained-release antibacterial gel system.

[0051] Example 5: Preparation of a sustained-release antibacterial gel system

[0052] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:220, stirred at 50°C for 1.2 h, and dried at 37°C and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in a 0.15M sodium hydroxide aqueous solution for 18 h and dried at 37°C and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and alcohol solvents were mixed at a mass ratio of 1:3:60 and shaken at 60°C for 24 h to obtain covalently grafted loaded salicylaldehyde sustained-release gel sheets. Add the promoter citrate-disodium hydrogen phosphate buffer (molar concentration of 0.1-0.2 mol / L, pH value of 4, and mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet of 8:1) and supplement with 2-methylbutyric acid (mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet of 20:1) to obtain the sustained-release antibacterial gel system.

[0053] Comparative Example 1

[0054] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:200, stirred at 50°C for 1.0 h, and dried at 37°C and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in a 0.1M sodium hydroxide aqueous solution for 24 h to neutralize, and dried at 37°C and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and an alcohol solvent were mixed at a mass ratio of 1:0:75 and shaken at 60°C for 24 h to obtain unloaded salicylaldehyde sustained-release gel sheets (see...). Figure 1 B). Add promoter citrate-disodium hydrogen phosphate buffer (molar concentration 0.1-0.2 mol / L, pH 4, mass ratio of promoter to sustained-release gel tablet 2:1) to obtain the sustained-release antibacterial gel system.

[0055] Comparative Example 2

[0056] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:200, stirred at 50°C for 1.0 h, and dried at 37°C and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in a 0.1M sodium hydroxide aqueous solution for 24 h to neutralize, and dried at 37°C and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and an alcohol solvent were mixed at a mass ratio of 1:0:75 and shaken at 60°C for 24 h to obtain unloaded salicylaldehyde sustained-release gel sheets. A promoter citrate-disodium hydrogen phosphate buffer (molar concentration 0.1-0.2 mol / L, pH 4, mass ratio to sustained-release gel sheets 2:1) was added, along with 2-methylbutyric acid (the amount used was the same as in Example 2), to obtain the sustained-release antibacterial gel system.

[0057] Comparative Example 3

[0058] Chitosan, organic acid, and water were mixed at a mass ratio of 3:1:200, stirred at 50℃ for 1.0 h, and dried at 37℃ and 40% relative humidity for 48 h to obtain acylated chitosan gel sheets. The acylated chitosan gel sheets were then immersed in 0.1M sodium hydroxide aqueous solution for 24 h to neutralize, and dried at 37℃ and 40% relative humidity for 24 h to obtain neutralized chitosan gel sheets. The neutralized chitosan gel sheets, salicylaldehyde, and an alcohol solvent were mixed at a mass ratio of 1:3:60 and shaken at 60℃ for 24 h to obtain covalently grafted salicylaldehyde sustained-release gel sheets. A promoter citrate-disodium hydrogen phosphate buffer (molar concentration 0.1-0.2 mol / L, pH 4, mass ratio of promoter to salicylaldehyde sustained-release gel sheet 8:1) was added to obtain the sustained-release antibacterial gel system.

[0059] Experimental Example 1: Inhibitory effect of sustained-release antibacterial gel on Rhizopus stolonifera

[0060] The inhibitory effects of the sustained-release antibacterial gel on the growth of the pathogenic fungus *Rhizopus stolonifer* hyphae in the examples and comparative examples were analyzed:

[0061] This experimental example uses a two-plate test for determination:

[0062] 1. Activate *Rhizopus stolonifer* on PDA medium at 28°C for 5 days. Then, add 5 mL of sterile water to a petri dish, obtain a fungal suspension by scraping the colonies with a scraper, and filter twice to obtain a spore suspension. Prepare a 1×10⁻⁶ spore suspension using a hemocytometer. 6 A spore suspension of spores / mL was thoroughly shaken on a vortex mixer for later use.

[0063] 2. First, pour PDA medium into one side of a 90mm diameter I plate and inoculate with 10μL of a medium containing 10... 6 A suspension of *Rhizopus spores* at a concentration of spores / mL was prepared. Then, a small petri dish (35 mm in diameter) was placed on the other side of the I plate. A salicylaldehyde slow-release gel sheet was added to the small petri dish, followed by 5 mL of citrate-disodium hydrogen phosphate buffer (0.1-0.2 mol / L, pH 4). The large petri dish was then covered and... Seal the container. Incubate at 28°C for 48 hours, and calculate the growth inhibition rate by monitoring fungal growth.

[0064] Table 1. Inhibition rate of sustained-release antibacterial gel against Rhizopus cremastogyne.

[0065]

[0066] The results showed that the sustained-release antibacterial gel system loaded with salicylaldehyde had a good inhibitory effect on the growth of Rhizopus cremastogyne; when used in combination with 2-methylbutyric acid, it had a significant synergistic antibacterial effect.

[0067] Experimental Example 2: Inhibitory effect of sustained-release antibacterial gel on oxidative damage in sweet potato

[0068] Malondialdehyde (MDA) is the end product of lipid peroxidation and can reflect the degree of cellular oxidative damage and membrane damage.

[0069] 1. Activate *Rhizopus stolonifer* on PDA medium at 28℃ for 5 days. Then, add 5 mL of sterile water to a petri dish, obtain a fungal suspension by scraping the colonies with a scraper, and filter twice to obtain a spore suspension. Prepare a 1×10⁻⁶ spore suspension using a hemocytometer. 8 A spore suspension of spores / mL was thoroughly shaken on a vortex mixer for later use.

[0070] 2. Select sweet potatoes that are uniformly ripe, uniform in size, and free from mechanical damage after harvesting. Rinse with tap water and air dry, then surface disinfect with 75% alcohol for 2 minutes and air dry at room temperature. Make three 5mm deep micro-wounds on one side of the sweet potato and inject 20μL of 1×10 [unspecified ingredient] into each wound. 6 A suspension of *Rhizopus spores* at a concentration of 1 / mL was prepared. After 24 hours of incubation, the mixture was transferred to a plastic storage box (with gauze at the bottom and covered with gauze to maintain moisture). The sustained-release antibacterial gel systems of Examples 2, 1, and 2 were also transferred to the storage box and stored at 28°C for 15 days. The content of the antibacterial gel was determined using an MDA kit to compare the preservation effects of different examples and comparative examples on sweet potatoes.

[0071] Table 2. MDA activity of sweet potatoes after 15 days of storage.

[0072]

[0073] The results showed that the sustained-release antibacterial gel system loaded with salicylaldehyde could significantly reduce oxidative damage to sweet potatoes; and when used in combination with 2-methylbutyric acid, it had a significant synergistic effect.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a sustained-release antibacterial gel system, characterized in that, Includes the following steps: 1) A loaded salicylaldehyde sustained-release gel tablets were prepared by acylation, neutralization, and covalent grafting. The acylation involved mixing chitosan, organic acid, and water at a mass ratio of 3:1:100-300, stirring at 40-60 ℃ for 0.2-2.0 h, and drying at 30-45 ℃ and 30%-45% relative humidity for 12-60 h to obtain acylated chitosan gel tablets. The covalent grafting involved mixing the neutralized chitosan gel tablets, salicylaldehyde, and alcohol solvent at a mass ratio of 1:1-10:50-100, and shaking at 50-70 ℃ for 15-40 h to obtain loaded salicylaldehyde sustained-release gel tablets. 2) The loaded salicylaldehyde sustained-release gel tablet is mixed with the promoter citrate-disodium hydrogen phosphate buffer and supplemented with 2-methylbutyric acid to obtain a sustained-release antibacterial gel system; the mass ratio of 2-methylbutyric acid to salicylaldehyde in the sustained-release gel tablet is 5-40:

1.

2. The method for preparing the sustained-release antibacterial gel system according to claim 1, characterized in that, In step 1), the organic acid is selected from one or more of acetic acid, formic acid, and citric acid.

3. The method for preparing the sustained-release antibacterial gel system according to claim 1, characterized in that, In step 1), the neutralization includes immersing the acylated chitosan gel sheet in a 0.05-0.2 M sodium hydroxide aqueous solution for 12-48 h, and drying it at 30-45℃ and 30%-45% relative humidity for 12-30 h to obtain the neutralized chitosan gel sheet.

4. The method for preparing the sustained-release antibacterial gel system according to claim 1, characterized in that, In step 1), the alcohol solvent is selected from one or more of ethanol, propylene glycol, glycerol, n-propanol, isopropanol, n-butanol, n-pentanol, and isopentanol.

5. The method for preparing the sustained-release antibacterial gel system according to claim 4, characterized in that, In step 1), the alcohol solvent is ethanol.

6. The method for preparing the sustained-release antibacterial gel system according to claim 1, characterized in that, In step 2), the molar concentration of the citrate-disodium hydrogen phosphate buffer is 0.1-0.2 mol / L, the pH value is 3-7, and the mass ratio of the citrate-disodium hydrogen phosphate buffer to the salicylaldehyde-loaded sustained-release gel sheet is 1-8:

1.

7. The sustained-release antibacterial gel system obtained by the preparation method of the sustained-release antibacterial gel system according to any one of claims 1-6.

8. The application of the sustained-release antibacterial gel system according to claim 7 in the preservation of agricultural products.

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