Agricultural composition containing composite chitosan and preparation method thereof

Abstract

The present invention belongs to the technical field of agricultural compositions, and in particular to an agricultural composition containing composite chitin and a preparation method thereof, comprising the following components by weight: 25 to 35 parts of a composite chitin solution, 40 to 50 parts of a double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid, and 10 to 20 parts of riboflavin; the preparation method of the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid is as follows: after the composite chitin is carboxymethylated, a composite carboxymethyl chitin hydrogel is obtained after ionic crosslinking, and then crosslinked with oxidized hyaluronic acid and loaded with DL-malic acid to obtain. The present invention adds a double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid, and the double-crosslinked composite carboxymethyl chitin hydrogel can enhance the adhesion to the surface of fruits and vegetables after spraying, so that the agricultural composition can be used on rainy days, reducing or avoiding being washed away by rainwater after use.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural compositions, and particularly relates to an agricultural composition containing composite chitosan and a preparation method thereof. Background Art

[0002] Plant growth regulators (PGRSs) can modulate plant growth and development at low concentrations. Based on their biological activity, they can be divided into various types, such as gibberellins, jasmonic acid, abscisic acid, and ethylene. These PGRSs influence plant morphology, growth, and development, as well as their ability to respond to environmental changes, by regulating biological processes such as cell division, elongation, differentiation, and organ development.

[0003] However, plant growth regulators attached to plants are susceptible to peeling, loss, or shedding in natural environments like rain and wind, thus losing their effectiveness and sometimes failing to fully exert their effects. In particular, during periods of high rainfall, such as the plum rain season, high humidity makes it difficult for the agents to adhere to the plants, leading to significant loss of the agents due to rainfall. This results in the forced application of additional agents, leading to increased costs, reduced operational efficiency, and increased environmental impact.

[0004] In addition, the influence of rainfall and wind can also cause the spread of plant pathogens and increase the risk of disease caused by physical damage to plants. Summary of the Invention

[0005] The object of the present invention is to provide an agricultural composition containing composite chitosan and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0007] An agricultural composition containing composite chitosan, comprising the following components by weight: 25-35 parts of composite chitosan solution, 40-50 parts of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 10-20 parts of riboflavin (vitamin B2);

[0008] The preparation method of the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid comprises the following steps: carboxymethylating the composite chitin, performing ionic crosslinking to obtain the composite carboxymethyl chitin hydrogel, and then crosslinking the composite carboxymethyl chitin hydrogel with oxidized hyaluronic acid and loading the hydrogel with DL-malic acid.

[0009] As a further improvement, the composite chitosan solution includes, by mass concentration, 10-30 wt% of oligosaccharides with a molecular weight of 200-2000, 20-40 wt% of oligosaccharides with a molecular weight of 2000-6000, and 40-60 wt% of polysaccharides with a molecular weight of 6000-10000.

[0010] The present invention also provides a method for preparing an agricultural composition containing composite chitosan, comprising the following steps:

[0011] S1, preparing composite carboxymethyl chitosan using the composite chitosan solution as a raw material, then configuring the composite carboxymethyl chitosan into a composite carboxymethyl chitosan solution, adding the composite carboxymethyl chitosan solution dropwise into a mixed ion solution of ferric chloride and calcium chloride, allowing the solution to stand, separating the lower layer, washing, and drying to obtain a composite carboxymethyl chitosan hydrogel;

[0012] S2, preparing a composite carboxymethyl chitosan hydrogel and oxidized hyaluronic acid into solutions respectively, mixing the two solutions in equal volumes, adding a DL-malic acid aqueous solution, allowing to stand, separating the lower layer, washing, and drying to obtain a DL-malic acid-loaded double-crosslinked composite carboxymethyl chitosan hydrogel;

[0013] S3. Place riboflavin in a 9 g / L sodium chloride solution and stir in a 60°C water bath until completely dissolved to obtain a riboflavin sodium chloride solution. Dissolve the double-cross-linked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in deionized water, then add the composite chitosan solution thereto, and slowly drop the riboflavin sodium chloride solution thereinto while adding with magnetic stirring at 800-1000 rpm. After the addition is completed, continue stirring for 20 minutes, and then homogenize at 20 MPa for 30 minutes to obtain an agricultural composition.

[0014] As a further improvement, in step S2, the preparation method of the mixed ion solution of ferric chloride and calcium chloride is: dissolving ferric chloride and calcium chloride in distilled water, respectively, to prepare 3% mass fraction ferric chloride solution and calcium chloride solution, respectively, and then mixing the ferric chloride solution and the calcium chloride solution in a mass ratio of 1:2.

[0015] As a further improvement, in step S2, the mass fraction of the composite carboxymethyl chitosan solution is 5%.

[0016] As a further improvement, in step S2, the volume ratio of the composite carboxymethyl chitosan solution to the mixed ion solution of ferric chloride and calcium chloride is 1-3:5, and the standing time is 60 minutes.

[0017] As a further improvement, in step S3, the oxidized hyaluronic acid is prepared by sodium periodate oxidation method.

[0018] As a further improvement, the composite chitosan is obtained by compounding oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000, and polysaccharides with a molecular weight of 6000 to 100000, and then dissolving them in distilled water at 20° C. to 80° C.

[0019] As a further improvement, the preparation method of the composite carboxymethyl chitosan is as follows: adding 80% by mass of sodium hydroxide solution and sodium lauryl sulfate to the composite chitosan solution, stirring thoroughly, standing at 4°C for 1 hour, and freezing overnight to obtain a mixed solution;

[0020] Isopropyl alcohol, monochloroacetic acid and sodium borohydride were added to the mixed solution, and the mixture was stirred in a constant temperature water bath at 25°C for 3 hours. After the reaction was completed, solid matter was obtained by filtration, and the solid matter was washed with an 80% volume fraction ethanol solution and placed in distilled water. The pH of the solution was adjusted to 7.0, and the clear liquid was obtained by filtration and ultrafiltration. It was then precipitated with acetone, and the precipitate obtained after centrifugation was freeze-dried to obtain composite carboxymethyl chitosan.

[0021] As a further improvement, the mass of the sodium lauryl sulfate is 0.4% of the mass of the composite chitosan solution, the mass ratio of the sodium hydroxide solution to the composite chitosan solution is 7:1; the amount of isopropyl alcohol added is 4 times the volume of sodium hydroxide, and the mass ratio of monochloroacetic acid to the composite chitosan solution is 3:1.

[0022] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0023] The present invention provides an agricultural composition containing composite chitosan. By adding a double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, the double-crosslinked composite carboxymethyl chitosan hydrogel can enhance the adhesion to the surface of fruits and vegetables after spraying, so that the agricultural composition can be used on rainy days, reducing or avoiding being washed away by rainwater after use. By adding DL-malic acid as a substance that promotes fruit growth, the added riboflavin and DL-malic acid synergistically act on the fruit growth process, especially for fruits rich in anthocyanins.

[0024] After use, the double-crosslinked composite carboxymethyl chitosan hydrogel of the agricultural composition can slowly release DL-malic acid, and the double-crosslinked composite carboxymethyl chitosan hydrogel has oxygen permeability and water retention, which can provide water for the growth of fruits and oxygen for the growth and development of fruits.

[0025] The double-crosslinked composite carboxymethyl chitosan hydrogel loses water after a period of time and forms a thin film on the outside of the fruit. At the same time, under the action of the composite chitosan, the film's permeability to oxygen is reduced and its permeability to carbon dioxide is increased, thereby inhibiting the respiration of the fruit and increasing the storage period of the fruit. The agricultural composition can provide DL-malic acid, oxygen, etc. to the fruit during the fruit growth stage and increase the fruit storage time during the fruit storage stage by reasonably setting the application time. It is generally applied about half a month before the fruit is picked.

[0026] The double-crosslinked composite carboxymethyl chitosan hydrogel of the present invention first forms a rigid network by chelating and crosslinking the carboxymethyl groups in the composite carboxymethyl chitosan with calcium ions and iron ions, and then crosslinks with oxidized hyaluronic acid to form a flexible network, so that the agricultural composition has high adhesion to the surface of fruits and vegetables.

[0027] During the research process, the inventors found that the use of calcium chloride solution alone as an ion solution has a weak chelating effect with the composite carboxymethyl chitin and cannot form a stable gel. Therefore, ferric chloride solution is added to form a stable gel. However, adding too much iron ions will cause the composite carboxymethyl chitin hydrogel to form a denser cross-linked network, with smaller molecular network gaps and reduced oxygen permeability. Therefore, by adjusting the ratio of ferric chloride solution and calcium chloride solution, oxygen permeability can be guaranteed while forming a stable gel. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0029] Example 1 An agricultural composition containing composite chitosan comprises the following components in parts by weight: 30 parts of composite chitosan solution, 45 parts of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 15 parts of riboflavin.

[0030] The composite chitin solution includes, by mass concentration, 30 wt% of oligosaccharides with a molecular weight of 200-2000, 20 wt% of oligosaccharides with a molecular weight of 2000-6000, and 50 wt% of polysaccharides with a molecular weight of 6000-10000.

[0031] This embodiment also provides a method for preparing the above agricultural composition containing composite chitosan, comprising the following steps:

[0032] S1. Preparation of composite chitin solution;

[0033] Oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000, and polysaccharides with a molecular weight of 6000 to 100000 are compounded at 20° C. and dissolved in distilled water to obtain a composite chitosan solution. The preparation methods of the oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000, and polysaccharides with a molecular weight of 6000 to 100000 are prior art and will not be described in detail herein.

[0034] S2. Preparation of composite carboxymethyl chitin;

[0035] To 10 g of the composite chitin solution, 70 g of 80% sodium hydroxide solution and 0.04 g of sodium dodecyl sulfate were added, stirred thoroughly and allowed to stand at 4 ° C for 1 h, then frozen at -20 ° C overnight, and then 196 mL of isopropanol and 30 g of monochloroacetic acid were added thereto while stirring, and then 0.2 g of sodium borohydride was added thereto, and the reaction was carried out in a constant temperature water bath at 25 ° C for 3 h. After the reaction was completed, the solid substance was filtered off, and the solid substance was washed with 80% ethanol solution by volume and placed in distilled water. The pH of the solution was adjusted to 7.0, and the clear liquid was filtered off and ultrafiltered with a molecular weight cutoff of 8000D. The precipitate was then precipitated with acetone, centrifuged at 500 rpm, and freeze-dried at -4 ° C for 30 min to obtain a composite carboxymethyl chitin, wherein the density of the 80% sodium hydroxide solution was 1.43 g / cm 3 ;

[0036] S3, preparation of composite carboxymethyl chitin hydrogel;

[0037] Dissolve ferric chloride in distilled water to prepare a 3% by mass ferric chloride solution, dissolve solid calcium chloride in distilled water to prepare a 3% by mass calcium chloride solution, and mix the ferric chloride solution and the calcium chloride solution in a mass ratio of 1:2 to obtain a mixed ion solution;

[0038] The composite carboxymethyl chitosan was dissolved in distilled water to prepare a composite carboxymethyl chitosan solution with a mass fraction of 5%.

[0039] 10 mL of the composite carboxymethyl chitosan solution was added dropwise into 50 mL of the mixed ion solution, and the mixture was allowed to stand for 60 min. The lower layer was separated and washed with deionized water, and then dried at 40 °C for 24 h to obtain the composite carboxymethyl chitosan hydrogel.

[0040] S4, preparation of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid;

[0041] Oxidized hyaluronic acid was prepared using a sodium periodate oxidation method. Specifically, 5 g of sodium hyaluronate was dissolved in 500 mL of ultrapure water, and 50 mL of a 53.5 mg / mL sodium periodate aqueous solution was added dropwise to the sodium hyaluronate solution with stirring. The mixture was then stirred in the dark for 2 h, and ethylene glycol was added to quench the unreacted sodium periodate. Stirring was continued for 1 h, and the mixture was then dialyzed and purified in ultrapure water for 3 days, and lyophilized to obtain the oxidized hyaluronic acid.

[0042] 40 mg of composite carboxymethyl chitosan hydrogel and 40 mg of oxidized hyaluronic acid were weighed and dissolved in 1 mL of ultrapure water to prepare a solution. The two solutions were then mixed in equal volumes and added with 20 mL of a 1 mg / L DL-malic acid aqueous solution. The solution was allowed to stand for 60 min, and the lower layer was separated. The solution was washed with deionized water and then dried at 40°C for 24 h to obtain 60 mg of a double-cross-linked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid.

[0043] S5. Place 15 g of riboflavin in 100 mL of 9 g / L sodium chloride solution and stir in a 60 °C water bath until completely dissolved. Dissolve 45 g of the double-cross-linked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in 50 mL of deionized water. Then add 30 g of the composite chitin solution. Slowly drop the riboflavin sodium chloride solution into it while magnetically stirring at 800 rpm. After the addition is complete, continue stirring for 20 minutes, and then homogenize at 20 MPa for 30 minutes.

[0044] Example 2 An agricultural composition containing composite chitosan comprises the following components in parts by weight: 25 parts of composite chitosan solution, 40 parts of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 10 parts of riboflavin.

[0045] The composite chitin solution includes, by mass concentration, 10 wt% of oligosaccharides with a molecular weight of 200-2000, 40 wt% of oligosaccharides with a molecular weight of 2000-6000, and 40 wt% of polysaccharides with a molecular weight of 6000-10000.

[0046] This embodiment also provides a method for preparing the above agricultural composition containing composite chitosan, comprising the following steps:

[0047] S1. Preparation of composite chitin solution;

[0048] Oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000, and polysaccharides with a molecular weight of 6000 to 100000 are compounded at 20° C. and dissolved in distilled water to obtain a composite chitosan solution;

[0049] S2. Preparation of composite carboxymethyl chitin;

[0050] To 10 g of the composite chitin solution, 70 g of 80% sodium hydroxide solution and 0.04 g of sodium dodecyl sulfate were added, stirred thoroughly and allowed to stand at 4 ° C for 1 h, then frozen at -20 ° C overnight, and then 196 mL of isopropanol and 30 g of monochloroacetic acid were added thereto while stirring, and then 0.2 g of sodium borohydride was added thereto, and the reaction was carried out in a constant temperature water bath at 25 ° C for 3 h. After the reaction was completed, the solid substance was filtered off, and the solid substance was washed with 80% ethanol solution by volume and placed in distilled water. The pH of the solution was adjusted to 7.0, and the clear liquid was filtered off and ultrafiltered with a molecular weight cutoff of 8000D. The precipitate was then precipitated with acetone, centrifuged at 500 rpm, and freeze-dried at -4 ° C for 30 min to obtain a composite carboxymethyl chitin, wherein the density of the 80% sodium hydroxide solution was 1.43 g / cm 3 ;

[0051] S3, preparation of composite carboxymethyl chitin hydrogel;

[0052] Dissolve ferric chloride in distilled water to prepare a 3% by mass ferric chloride solution, dissolve solid calcium chloride in distilled water to prepare a 3% by mass calcium chloride solution, and mix the ferric chloride solution and the calcium chloride solution in a mass ratio of 1:2 to obtain a mixed ion solution;

[0053] The composite carboxymethyl chitosan was dissolved in distilled water to prepare a composite carboxymethyl chitosan solution with a mass fraction of 5%.

[0054] 30 mL of the composite carboxymethyl chitosan solution was added dropwise into 50 mL of the mixed ion solution, and the mixture was allowed to stand for 60 min. The lower layer was separated and washed with deionized water, and then dried at 40 °C for 24 h to obtain the composite carboxymethyl chitosan hydrogel.

[0055] S4, preparation of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid;

[0056] Oxidized hyaluronic acid was prepared by sodium periodate oxidation method, the specific method was the same as that in Example 1;

[0057] 40 mg of composite carboxymethyl chitosan hydrogel and 40 mg of oxidized hyaluronic acid were weighed and dissolved in 1 mL of ultrapure water to prepare a solution. The two solutions were then mixed in equal volumes and added with 20 mL of a 1 mg / L DL-malic acid aqueous solution. The solution was allowed to stand for 60 min, and the lower layer was separated. The solution was washed with deionized water and then dried at 40°C for 24 h to obtain a double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid.

[0058] S5. Place 10 g of riboflavin in 80 mL of 9 g / L sodium chloride solution and stir in a 60°C water bath until completely dissolved. Dissolve 40 g of double-cross-linked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in 45 mL of deionized water. Then add 25 g of the composite chitin solution. Slowly drop the riboflavin sodium chloride solution into it while magnetically stirring at 1000 rpm. Continue stirring for 20 minutes after the addition is complete, and then homogenize at 20 MPa for 30 minutes.

[0059] Example 3 An agricultural composition containing composite chitosan comprises the following components in parts by weight: 35 parts of composite chitosan solution, 50 parts of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 20 parts of riboflavin.

[0060] The composite chitin solution includes, by mass concentration, 20 wt % of oligosaccharides with a molecular weight of 200-2000, 30 wt % of oligosaccharides with a molecular weight of 2000-6000, and 60 wt % of polysaccharides with a molecular weight of 6000-10000.

[0061] This embodiment also provides a method for preparing the above agricultural composition containing composite chitosan, comprising the following steps:

[0062] S1. Preparation of composite chitin solution;

[0063] Oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000, and polysaccharides with a molecular weight of 6000 to 100000 are compounded at 20° C. and dissolved in distilled water to obtain a composite chitosan solution;

[0064] S2. Preparation of composite carboxymethyl chitin;

[0065] To 10 g of the composite chitin solution, 70 g of 80% sodium hydroxide solution and 0.04 g of sodium dodecyl sulfate were added, stirred thoroughly and allowed to stand at 4 ° C for 1 h, then frozen at -20 ° C overnight, and then 196 mL of isopropanol and 30 g of monochloroacetic acid were added thereto while stirring, and then 0.2 g of sodium borohydride was added thereto, and the reaction was carried out in a constant temperature water bath at 25 ° C for 3 h. After the reaction was completed, the solid substance was filtered off, and the solid substance was washed with 80% ethanol solution by volume and placed in distilled water. The pH of the solution was adjusted to 7.0, and the clear liquid was filtered off and ultrafiltered with a molecular weight cutoff of 8000D. The precipitate was then precipitated with acetone, centrifuged at 500 rpm, and freeze-dried at -4 ° C for 30 min to obtain a composite carboxymethyl chitin, wherein the density of the 80% sodium hydroxide solution was 1.43 g / cm 3 ;

[0066] S3, preparation of composite carboxymethyl chitin hydrogel;

[0067] Dissolve ferric chloride in distilled water to prepare a 3% by mass ferric chloride solution, dissolve solid calcium chloride in distilled water to prepare a 3% by mass calcium chloride solution, and mix the ferric chloride solution and the calcium chloride solution in a mass ratio of 1:2 to obtain a mixed ion solution;

[0068] The composite carboxymethyl chitosan was dissolved in distilled water to prepare a composite carboxymethyl chitosan solution with a mass fraction of 5%.

[0069] 40 mL of the composite carboxymethyl chitosan solution was added dropwise into 50 mL of the mixed ion solution, and the mixture was allowed to stand for 60 min. The lower layer was separated and washed with deionized water, and then dried at 40 °C for 24 h to obtain the composite carboxymethyl chitosan hydrogel.

[0070] S4, preparation of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid;

[0071] Oxidized hyaluronic acid was prepared by sodium periodate oxidation method, the specific method was the same as that in Example 1;

[0072] 40 mg of composite carboxymethyl chitosan hydrogel and 40 mg of oxidized hyaluronic acid were weighed and dissolved in 1 mL of ultrapure water to prepare a solution. The two solutions were then mixed in equal volumes and added with 20 mL of a 1 mg / L DL-malic acid aqueous solution. The solution was allowed to stand for 60 min, and the lower layer was separated. The solution was washed with deionized water and then dried at 40°C for 24 h to obtain a double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid.

[0073] S5. Place 20 g of riboflavin in 140 mL of 9 g / L sodium chloride solution and stir in a 60 °C water bath until completely dissolved. Dissolve 50 g of the double-cross-linked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in 55 mL of deionized water. Then add 35 g of the composite chitin solution. Slowly drop the riboflavin sodium chloride solution into it while magnetically stirring at 900 rpm. After the addition is complete, continue stirring for 20 minutes, and then homogenize at 20 MPa for 30 minutes.

[0074] Comparative Example 1 This comparative example provides an agricultural composition containing composite chitosan and a preparation method thereof. The components and preparation method of the agricultural composition are the same as those in Example 1, except that, in the preparation process of the composite carboxymethyl chitosan hydrogel, the ferric chloride solution and the calcium chloride solution in the mixed ion solution are mixed in a mass ratio of 1:1.

[0075] Comparative Example 2 This comparative example provides an agricultural composition containing composite chitosan and a preparation method thereof. The components and preparation method of the agricultural composition are the same as those in Example 1, except that, in the preparation process of the composite carboxymethyl chitosan hydrogel, the ferric chloride solution and the calcium chloride solution in the mixed ion solution are mixed in a mass ratio of 2:1.

[0076] Comparative Example 3 This comparative example provides an agricultural composition containing composite chitosan and a preparation method thereof, which comprises the following components in parts by weight: 30 parts of composite chitosan solution, 45 parts of DL-malic acid, and 15 parts of riboflavin.

[0077] In the preparation method, 15 g of riboflavin was placed in 100 mL of a 9 g / L sodium chloride solution and stirred in a 60°C water bath until completely dissolved. 30 g of the composite chitosan solution and 45 g of DL-malic acid were added to 50 mL of deionized water. The riboflavin sodium chloride solution was slowly added dropwise at 800 rpm while magnetically stirring. After the addition was complete, stirring was continued for 20 minutes, and then homogenization was performed at 20 MPa for 30 minutes.

[0078] Comparative Example 4 This comparative example provides an agricultural composition containing composite chitosan and a preparation method thereof, which comprises the following components in parts by weight: 30 parts of composite chitosan solution, 45 parts of composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 15 parts of riboflavin.

[0079] Among them, the preparation method of the composite carboxymethyl chitin hydrogel loaded with DL-malic acid is: 40 mL of the composite carboxymethyl chitin solution is added dropwise into 50 mL of the mixed ion solution, and then 20 mL of a DL-malic acid aqueous solution with a concentration of 1 mg / mL is added, and the mixture is allowed to stand for 60 minutes. The lower layer is separated and washed with deionized water, and then dried at 40°C for 24 hours to obtain the composite carboxymethyl chitin hydrogel loaded with DL-malic acid.

[0080] Comparative Example 5 This comparative example provides an agricultural composition containing composite chitosan and a preparation method thereof, which comprises the following components in parts by weight: 45 parts of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid and 15 parts of riboflavin.

[0081] Grape fruits and tomato fruits from the same planting base were selected as experimental models. First, deionized water was used to gently rinse the dust and impurities on the outer surfaces of the grape fruits and tomato fruits. After rinsing, the fruits were placed at room temperature and protected from light to dry naturally. Then, the grape fruits and tomato fruits were divided into six groups, each with 3 parts, namely Group 1 of Example 1 and Groups 1-5 of Comparative Examples. The six groups of models were sprayed with 5 mL of the agricultural composition prepared in Example 1 and Comparative Examples 1-5 using a small spray device. At 0 h, 24 h, and 48 h after spraying the agricultural composition, the three models in each group were uniformly sprayed with deionized water at a flow rate of 15 mL / min from 20 cm above at a 45° angle to simulate rain scouring behavior. Each group was rain-washed for 45 minutes.

[0082] Then, 0.5 g of fruit from each model group was added to 10 mL of phosphate buffered saline solution, and then ultrasonicated at 2 MHz for 1 min to completely release DL-malic acid. The fruit was then centrifuged at 500 rpm for 10 min, and the supernatant was taken. The content of DL-malic acid in the supernatant was determined by liquid chromatography. The results are shown in Tables 1 and 2.

[0083] Table 1 DL-malic acid content results of six groups of grape models

[0084]

[0085] Table 2 DL-malic acid content results of six groups of tomato models

[0086]

[0087] As can be seen from Tables 1 and 2, the content of the agricultural composition remaining on the fruit in Example 1, Comparative Example 1, and Comparative Example 2 at 0 h, 24 h, and 48 h was higher than that in Comparative Examples 3-4. This indicates that the double-crosslinked composite carboxymethyl chitin hydrogel of the present invention has high adhesion to the surface of fruits and vegetables, can reduce or avoid being washed away by rainwater after use, and does not affect the efficacy when used on rainy days. In addition, a comparison of the experimental results of Comparative Examples 3 and 4 shows that the composite carboxymethyl chitin hydrogel loaded with DL-malic acid has a certain adhesion to the surface of fruits and vegetables, but its adhesion is not as high as that of the double-crosslinked composite carboxymethyl chitin hydrogel of the present invention.

[0088] Six groups of plants were randomly selected from the experimental vineyard, with 8 plants in each group, for fruit growth and development experiments. Three weeks after flowering, all six groups of plants were sprayed with 5 mL of a 20 mg / mL concentration. Other conditions were followed according to actual conditions. After the fruits matured, the berry weight and berry coloration were measured. After the fruits were picked, they were stored in the same environment at room temperature of 25°C. The time when rot lesions appeared on the fruit surface was recorded. The results are shown in Table 3.

[0089] Table 3 Fruit weight, fruit coloration and storage time of the six groups of plants

[0090]

[0091] As can be seen from Table 3, the average weight of the fruit and the degree of coloration of the fruit obtained in Example 1 are higher than those in Comparative Examples 1-2. This is because the double-crosslinked composite carboxymethyl chitosan hydrogel prepared from the mixed ion solution obtained by the ferric chloride solution and the calcium chloride solution in a mass ratio of 1:2 in the present invention has higher oxygen permeability, which is beneficial to the growth and development of the fruit. The storage time of the fruit in Example 1 and Comparative Examples 1-2 is longer than that in Comparative Example 3 and Comparative Example 5, and the storage time of Comparative Example 5 is longer than that of Comparative Example 3. This is because the double-crosslinked composite carboxymethyl chitosan hydrogel of the present invention forms a protective film on the surface of the fruit after complete dehydration, that is, during the storage process of the fruit. At the same time, under the action of the composite chitosan, the permeation of oxygen is prevented, the permeability of carbon dioxide is increased, and the respiration of the fruit during storage is reduced. In addition, the composite chitosan can prevent bacteria from invading the fruit.

[0092] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. An agricultural composition containing composite chitosan, characterized in that: The invention comprises the following components in parts by weight: 25 to 35 parts of a composite chitosan solution, 40 to 50 parts of a double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 10 to 20 parts of riboflavin; The preparation method of the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid comprises: carboxymethylating the composite chitin, performing ionic crosslinking to obtain the composite carboxymethyl chitin hydrogel, and then crosslinking the composite carboxymethyl chitin hydrogel with oxidized hyaluronic acid and loading the hydrogel with DL-malic acid to obtain the composite carboxymethyl chitin hydrogel; The preparation method of the composite carboxymethyl chitosan hydrogel specifically comprises the following steps: preparing composite carboxymethyl chitosan from a composite chitosan solution as a raw material, then configuring the composite carboxymethyl chitosan into a composite carboxymethyl chitosan solution, dropwise adding the composite carboxymethyl chitosan solution into a mixed ion solution of ferric chloride and calcium chloride, allowing the solution to stand, separating the lower layer, washing, and drying to obtain the composite carboxymethyl chitosan hydrogel; The preparation method of the mixed ion solution of ferric chloride and calcium chloride is as follows: ferric chloride and calcium chloride are respectively dissolved in distilled water to prepare 3% by mass ferric chloride solution and calcium chloride solution, respectively, and then the ferric chloride solution and the calcium chloride solution are mixed in a mass ratio of 1:

2.

2. The agricultural composition containing composite chitosan according to claim 1, characterized in that The composite chitin solution comprises, by mass concentration, 10-30 wt% of oligosaccharides with a molecular weight of 200-2000, 20-40 wt% of oligosaccharides with a molecular weight of 2000-6000, and 40-60 wt% of polysaccharides with a molecular weight of 6000-10000.

3. The method for preparing the agricultural composition containing composite chitosan according to claim 1, characterized in that: The following steps are involved: S1, preparing composite carboxymethyl chitosan using the composite chitosan solution as a raw material, then configuring the composite carboxymethyl chitosan into a composite carboxymethyl chitosan solution, adding the composite carboxymethyl chitosan solution dropwise into a mixed ion solution of ferric chloride and calcium chloride, allowing the solution to stand, separating the lower layer, washing, and drying to obtain a composite carboxymethyl chitosan hydrogel; The preparation method of the mixed ion solution of ferric chloride and calcium chloride is as follows: ferric chloride and calcium chloride are respectively dissolved in distilled water to prepare 3% by mass ferric chloride solution and calcium chloride solution, and then the ferric chloride solution and the calcium chloride solution are mixed in a mass ratio of 1:2 to obtain a mixed ion solution. S2, preparing a composite carboxymethyl chitosan hydrogel and oxidized hyaluronic acid into solutions respectively, mixing the two solutions in equal volumes, adding a DL-malic acid aqueous solution, allowing to stand, separating the lower layer, washing, and drying to obtain a DL-malic acid-loaded double-crosslinked composite carboxymethyl chitosan hydrogel; S3. Place riboflavin in a 9 g / L sodium chloride solution and stir in a 60°C water bath until completely dissolved to obtain a riboflavin sodium chloride solution. Dissolve the double-cross-linked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in deionized water, then add the composite chitosan solution thereto, and slowly drop the riboflavin sodium chloride solution thereinto while adding with magnetic stirring at 800-1000 rpm. After the addition is completed, continue stirring for 20 minutes, and then homogenize at 20 MPa for 30 minutes to obtain an agricultural composition.

4. The method for preparing the agricultural composition containing composite chitosan according to claim 3, wherein: In step S1, the mass fraction of the composite carboxymethyl chitosan solution is 5%.

5. The method for preparing the agricultural composition containing composite chitosan according to claim 3, wherein: In step S1, the volume ratio of the composite carboxymethyl chitosan solution to the mixed ion solution of ferric chloride and calcium chloride is 1-3:5, and the standing time is 60 minutes.

6. The method for preparing the agricultural composition containing composite chitosan according to claim 3, wherein: In step S2, the oxidized hyaluronic acid is prepared by sodium periodate oxidation method.

7. The method for preparing the agricultural composition containing composite chitosan according to claim 3, wherein: The composite chitin is obtained by compounding oligosaccharides with a molecular weight of 200 to 2000, oligosaccharides with a molecular weight of 2000 to 6000 and polysaccharides with a molecular weight of 6000 to 100000 at a temperature of 20 to 80 DEG C and then dissolving them in distilled water.

8. The method for preparing the agricultural composition containing composite chitosan according to claim 3, wherein: The composite carboxymethyl chitosan preparation method comprises: adding 80% by mass of sodium hydroxide solution and sodium lauryl sulfate to the composite chitosan solution, stirring thoroughly, standing at 4° C. for 1 hour, and freezing overnight to obtain a mixed solution; Isopropyl alcohol, monochloroacetic acid and sodium borohydride were added to the mixed solution, and the mixture was stirred in a constant temperature water bath at 25°C for 3 hours. After the reaction was completed, solid matter was obtained by filtration, and the solid matter was washed with an 80% volume fraction ethanol solution and placed in distilled water. The pH of the solution was adjusted to 7.0, and the clear liquid was obtained by filtration and ultrafiltration. It was then precipitated with acetone, and the precipitate obtained after centrifugation was freeze-dried to obtain composite carboxymethyl chitosan.

9. The method for preparing the agricultural composition containing composite chitosan according to claim 8, characterized in that: The mass of the sodium lauryl sulfate is 0.4% of the mass of the composite chitosan solution, the mass ratio of the sodium hydroxide solution to the composite chitosan solution is 7:1; the amount of the added isopropyl alcohol is 4 times the volume of the sodium hydroxide, and the mass ratio of monochloroacetic acid to the composite chitosan solution is 3:1.

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