Agricultural composition containing composite chitin and preparation method thereof

Abstract

The invention belongs to the technical field of agricultural compositions, and particularly relates to an agricultural composition containing composite chitin and a preparation method thereof.The agricultural composition is prepared from, by weight, 25-35 parts of a composite chitin solution, 40-50 parts of double-crosslinking composite carboxymethyl chitin hydrogel loaded with DL-malic acid and 10-20 parts of riboflavin; the preparation method of the double-crosslinking composite carboxymethyl chitin hydrogel loaded with the DL-malic acid comprises the following steps: performing carboxymethylation on the composite chitin, performing ionic crosslinking to obtain composite carboxymethyl chitin hydrogel, then crosslinking the composite carboxymethyl chitin hydrogel with oxidized hyaluronic acid, and loading the DL-malic acid to obtain the double-crosslinking composite carboxymethyl chitin hydrogel loaded with the DL-malic acid. According to the invention, the DL-malic acid loaded bi-crosslinking composite carboxymethyl chitin hydrogel is added, and the bi-crosslinking composite carboxymethyl chitin hydrogel can enhance the adhesiveness with the outer surfaces of fruits and vegetables after being sprayed, so that the agricultural composition can be used in rainy days, and the situation that the agricultural composition is washed away by rainwater after being used is reduced or avoided.

Description

Technical Field

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

[0002] Plant growth regulators can regulate plant growth and development at low concentrations. According to their biological activity, plant growth regulators can be divided into many types, such as gibberellins, jasmonic acid, abscisic acid and ethylene. These growth regulators regulate biological processes such as cell division, elongation, differentiation and organ development, thereby affecting the plant's morphological construction, growth and development, and its ability to cope with environmental changes.

[0003] However, plant growth regulators attached to plants are easily peeled off, lost or shed in natural environments such as rain and wind, thus losing their effectiveness and sometimes failing to fully exert their effects. In particular, in seasons with frequent rainfall such as the plum rain season, it is difficult for the agent to be fixed to the plant in a high humidity environment, and a large amount of the agent is lost due to rainfall. As a result, the additional spreading of the agent is forced, causing problems such as increased costs, reduced operating efficiency, and increased environmental load.

[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: An agricultural composition containing composite chitosan, comprising the following components by weight: 25-35 parts of composite chitosan solution, 40-50 parts of double cross-linked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 10-20 parts of riboflavin (vitamin B2); The preparation method of the double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid is as follows: after the composite chitosan is carboxymethylated, the composite carboxymethyl chitosan hydrogel is obtained by ion crosslinking, and then the composite carboxymethyl chitosan hydrogel is crosslinked with oxidized hyaluronic acid and loaded with DL-malic acid to obtain the composite carboxymethyl chitosan hydrogel.

[0007] As a further improvement, the composite chitosan solution includes, by mass concentration, 10-30wt% of oligosaccharides with a molecular weight of 200-2000, 20-40wt% of oligosaccharides with a molecular weight of 2000-6000, and 40-60wt% of polysaccharides with a molecular weight of 6000-10000.

[0008] The present invention also provides a preparation method of an agricultural composition containing composite chitin, which comprises the following steps: S1. Using the composite chitin solution as a raw material to prepare composite carboxymethyl chitin, then configuring the composite carboxymethyl chitin into a composite carboxymethyl chitin solution, dropwise adding the composite carboxymethyl chitin solution into a mixed ionic solution of ferric chloride and calcium chloride, standing and separating the lower-layer substance, washing and drying to obtain a composite carboxymethyl chitin hydrogel; S2. Preparing the composite carboxymethyl chitin hydrogel and oxidized hyaluronic acid into solutions respectively, mixing the two solutions in equal volume, adding an aqueous solution of DL-malic acid, standing and separating the lower-layer substance, washing and drying to obtain a double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; S3. Placing riboflavin in a 9 g / L sodium chloride solution, stirring in a water bath at 60 °C until completely dissolved to obtain a sodium chloride solution of riboflavin, dissolving the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in deionized water, then adding a composite chitin solution thereto, and slowly dropping the sodium chloride solution of riboflavin into it, magnetically stirring while adding under the condition of 800 - 1000 rpm, continuing to stir for 20 minutes after dropping, and then performing homogenization treatment at 20 MPa for 30 min to obtain the agricultural composition.

[0009] As a further improvement, in step S2, the preparation method of the mixed ionic solution of ferric chloride and calcium chloride is: dissolving ferric chloride and calcium chloride in distilled water respectively, configuring a 3% mass fraction ferric chloride solution and a calcium chloride solution respectively, and then mixing the ferric chloride solution and the calcium chloride solution according to a mass ratio of 1:2.

[0010] As a further improvement, in step S2, the mass fraction of the composite carboxymethyl chitin solution is 5%.

[0011] As a further improvement, in step S2, the volume ratio of the composite carboxymethyl chitin solution to the mixed ionic solution of ferric chloride and calcium chloride is 1 - 3:5, and the standing time is 60 min.

[0012] As a further improvement, in step S3, the oxidized hyaluronic acid is prepared by the sodium periodate oxidation method.

[0013] As a further improvement, the composite chitin is obtained by mixing oligosaccharides with a molecular weight of 200 - 2000, oligosaccharides with a molecular weight of 2000 - 6000, and polysaccharides with a molecular weight of 6000 - 100000 at 20 °C - 80 °C and then dissolving them in distilled water.

[0014] As a further improvement, the preparation method of the composite carboxymethyl chitin is as follows: Add a sodium hydroxide solution with a mass fraction of 80% and sodium dodecyl sulfate to the composite chitin solution, stir well, let it stand at 4 °C for 1 h, and freeze overnight to obtain a mixed solution; Add isopropanol, monochloroacetic acid and sodium borohydride to the mixed solution, stir and react in a constant temperature water bath at 25 °C for 3 h. After the reaction is completed, filter to obtain a solid substance. Wash the solid substance with an ethanol solution with a volume fraction of 80%, place it in distilled water, adjust the pH of the solution to 7.0, filter to obtain a clear liquid, then ultrafilter, and then precipitate with acetone. The precipitate obtained after centrifugal separation is freeze-dried to obtain composite carboxymethyl chitin.

[0015] As a further improvement, the mass of the sodium dodecyl sulfate is 0.4% of the mass of the composite chitin solution, and the mass ratio of the sodium hydroxide solution to the composite chitin solution is 7:1; the addition amount of the isopropanol is 4 times the volume of the sodium hydroxide, and the mass ratio of the monochloroacetic acid to the composite chitin solution is 3:1.

[0016] Due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows: An agricultural composition containing composite chitin provided by the present invention, by adding a double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid, the double-crosslinked composite carboxymethyl chitin hydrogel can enhance the adhesion to the surface of fruits and vegetables after spraying, enabling the agricultural composition to be used in rainy days, reducing or avoiding being washed away by rainwater after use. By adding DL-malic acid as a substance to promote fruit growth, the added riboflavin and DL-malic acid act synergistically in the fruit growth process, especially for some fruits rich in anthocyanins.

[0017] After the agricultural composition is used, the double-crosslinked composite carboxymethyl chitin hydrogel can play a slow-release role for DL-malic acid, and the double-crosslinked composite carboxymethyl chitin hydrogel has oxygen permeability and water retention, which can not only provide water for the fruit growth process, but also provide oxygen for the growth and development of fruits.

[0018] The double-crosslinked composite carboxymethyl chitin hydrogel loses water after a period of time, forming a thin film on the outside of the fruit. At the same time, under the action of the composite chitin, the oxygen permeability of the thin film decreases and the carbon dioxide permeability increases, inhibiting the fruit respiration and increasing the storage period of the fruit. The agricultural composition can provide DL-malic acid, oxygen, etc. for the fruit during the fruit growth stage by reasonably setting the application time, and increase the fruit storage time during the fruit storage stage, generally applied about half a month before fruit picking.

[0019] In the present invention, the double-crosslinked composite carboxymethyl chitosan hydrogel first forms a rigid network by chelating and crosslinking carboxymethyl in the composite carboxymethyl chitosan with calcium ions and iron ions, and then forms a flexible network by crosslinking with oxidized hyaluronic acid, so that the adhesion of the agricultural composition to the surface of fruits and vegetables is high.

[0020] During the research process, the inventors found that when using calcium chloride solution alone as the ionic solution, the chelation with the composite carboxymethyl chitosan is relatively small and a stable gel cannot be formed. Therefore, ferric chloride solution is added to form a stable gel. However, too much addition of iron ions will cause the composite carboxymethyl chitosan hydrogel to form a denser crosslinked network with smaller network voids between molecules and reduced oxygen permeability. Therefore, by adjusting the ratio of ferric chloride solution and calcium chloride solution, the oxygen permeability is ensured while a stable gel is formed. Specific embodiments

[0021] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present invention. Conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0022] Example 1 An agricultural composition containing composite chitosan, by weight, comprises the following components: 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.

[0023] In the composite chitosan solution, by mass concentration, it comprises 30 wt% oligosaccharides with a molecular weight of 200 - 2000, 20 wt% oligosaccharides with a molecular weight of 2000 - 6000, and 50 wt% polysaccharides with a molecular weight of 6000 - 10000.

[0024] This example also provides a preparation method of the above agricultural composition containing composite chitosan, comprising the following steps: S1. Preparation of the composite chitosan solution; Oligosaccharides with a molecular weight of 200 - 2000, oligosaccharides with a molecular weight of 2000 - 6000, and polysaccharides with a molecular weight of 6000 - 100000 are compounded at 20°C and then dissolved in distilled water to obtain a composite chitin solution. The preparation methods of oligosaccharides with a molecular weight of 200 - 2000, oligosaccharides with a molecular weight of 2000 - 6000, and polysaccharides with a molecular weight of 6000 - 100000 are prior arts and will not be elaborated here; S2. Preparation of composite carboxymethyl chitin; Add 70 g of sodium hydroxide solution with a mass fraction of 80% and 0.04 g of sodium dodecyl sulfate to 10 g of the composite chitin solution. After stirring well, let it stand at 4°C for 1 h, then freeze it overnight at -20°C. Then add 196 mL of isopropanol and 30 g of monochloroacetic acid to it, stirring while adding. Then add 0.2 g of sodium borohydride and react in a constant temperature water bath at 25°C for 3 h. After the reaction is completed, filter to obtain a solid substance. Wash the solid substance with an ethanol solution with a volume fraction of 80% and then place it in distilled water. Adjust the pH of the solution to 7.0. After filtering to obtain a clear liquid, ultrafilter it with a molecular weight cut-off of 8000 D. Then precipitate it with acetone and centrifuge the precipitate at 500 rpm. Freeze-dry it at -4°C for 30 min to obtain composite carboxymethyl chitin, where the density of the sodium hydroxide solution with a mass fraction of 80% is 1.43 g / cm 3 ; S3. Preparation of composite carboxymethyl chitin hydrogel; Dissolve ferric chloride in distilled water to prepare a ferric chloride solution with a mass fraction of 3%. Dissolve calcium chloride solid in distilled water to prepare a calcium chloride solution with a mass fraction of 3%. Mix the ferric chloride solution and the calcium chloride solution according to a mass ratio of 1:2 to obtain a mixed ionic solution; Dissolve the composite carboxymethyl chitin in distilled water to prepare a composite carboxymethyl chitin solution with a mass fraction of 5%; Drop 10 mL of the composite carboxymethyl chitin solution into 50 mL of the mixed ionic solution drop by drop, let it stand for 60 min, separate the lower layer substance and wash it with deionized water, then dry it at 40°C for 24 h to obtain the composite carboxymethyl chitin hydrogel; S4. Preparation of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; Prepare oxidized hyaluronic acid by sodium periodate oxidation method. Specifically, dissolve 5 g of sodium hyaluronate in 500 mL of ultrapure water, and drop 50 mL of a sodium periodate aqueous solution with a concentration of 53.5 mg / mL into the sodium hyaluronate solution, stirring while dropping. Then stir the mixture in the dark for 2 h, add ethylene glycol to quench the unreacted sodium periodate, and continue to stir for 1 h. Then dialyze and purify it in ultrapure water for 3 days and freeze-dry it to obtain oxidized hyaluronic acid; Weigh 40 mg of composite carboxymethyl chitosan hydrogel and 40 mg of oxidized hyaluronic acid respectively, dissolve them in 1 mL of ultrapure water to prepare solutions, then mix the two solutions in equal volume and add them to 20 mL of DL-malic acid aqueous solution with a concentration of 1 mg / L. After standing for 60 min, separate the lower layer substance, wash it with deionized water, and then dry it at 40 °C for 24 h to obtain 60 mg of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid; S5. Place 15 g of riboflavin in 100 mL of 9 g / L sodium chloride solution, stir in a water bath at 60 °C until completely dissolved. Dissolve 45 g of double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid in 50 mL of deionized water, then add 30 g of composite chitosan solution to it. Slowly drip the riboflavin sodium chloride solution into it, and stir magnetically while adding at 800 rpm. After the addition is completed, continue to stir for 20 minutes, and then homogenize at 20 MPa for 30 min.

[0025] Example 2. An agricultural composition containing composite chitosan, by weight, comprises the following components: 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.

[0026] In the composite chitosan solution, by mass concentration, it includes 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.

[0027] This example also provides a preparation method of the above agricultural composition containing composite chitosan, which includes the following steps: S1. Preparation of composite chitosan solution; Mix oligosaccharides with a molecular weight of 200 - 2000, oligosaccharides with a molecular weight of 2000 - 6000, and polysaccharides with a molecular weight of 6000 - 100000 at 20 °C and dissolve them in distilled water to obtain a composite chitosan solution; S2. Preparation of composite carboxymethyl chitosan; Add 70 g of sodium hydroxide solution with a mass fraction of 80% and 0.04 g of sodium dodecyl sulfate to 10 g of the composite chitin solution. After stirring well, let it stand for 1 h at 4 °C, then freeze it overnight at -20 °C. Then add 196 mL of isopropanol and 30 g of monochloroacetic acid to it, stirring while adding. Then add 0.2 g of sodium borohydride and react at a constant temperature of 25 °C for 3 h. After the reaction is completed, filter to obtain a solid substance. Wash the solid substance with an ethanol solution with a volume fraction of 80% and then place it in distilled water. Adjust the pH of the solution to 7.0, filter to obtain a clear liquid and then ultrafilter it with a molecular weight cut-off of 8000 D. Then precipitate it with acetone, centrifuge the precipitate at 500 rpm, and freeze-dry it at -4 °C for 30 min to obtain composite carboxymethyl chitin, where the density of the sodium hydroxide solution with a mass fraction of 80% is 1.43 g / cm 3 ; S3. Preparation of composite carboxymethyl chitin hydrogel; Dissolve ferric chloride in distilled water to prepare a ferric chloride solution with a mass fraction of 3%, dissolve calcium chloride solid in distilled water to prepare a calcium chloride solution with a mass fraction of 3%, and mix the ferric chloride solution and the calcium chloride solution according to a mass ratio of 1:2 to obtain a mixed ionic solution; Dissolve composite carboxymethyl chitin in distilled water to prepare a composite carboxymethyl chitin solution with a mass fraction of 5%; Dropwise add 30 mL of the composite carboxymethyl chitin solution into 50 mL of the mixed ionic solution, let it stand for 60 min, separate the lower layer substance and wash it with deionized water, then dry it at 40 °C for 24 h to obtain the composite carboxymethyl chitin hydrogel; S4. Preparation of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; Prepare oxidized hyaluronic acid by the sodium periodate oxidation method, and the specific method is the same as that in Example 1; Weigh 40 mg of the composite carboxymethyl chitin hydrogel and 40 mg of oxidized hyaluronic acid and dissolve them in 1 mL of ultrapure water respectively to prepare solutions. Then mix the two solutions in equal volume and add 20 mL of a DL-malic acid aqueous solution with a concentration of 1 mg / L. Let it stand for 60 min, then separate the lower layer substance, wash it with deionized water, and then dry it at 40 °C for 24 h to obtain the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; S5. Place 10 g of riboflavin in 80 mL of a 9 g / L sodium chloride solution, stir in a water bath at 60 °C until completely dissolved. Dissolve 40 g of the double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid in 45 mL of deionized water, then add 25 g of the composite chitosan solution thereto, and slowly drip the riboflavin sodium chloride solution into it. While adding, stir magnetically under the condition of 1000 rpm. After the addition is completed, continue to stir for 20 minutes, and then homogenize at 20 MPa for 30 min.

[0028] Example 3. An agricultural composition containing composite chitosan, by weight, comprises the following components: 35 parts of the composite chitosan solution, 50 parts of the double-crosslinked composite carboxymethyl chitosan hydrogel loaded with DL-malic acid, and 20 parts of riboflavin.

[0029] In the composite chitosan solution, by mass concentration, it comprises 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.

[0030] This example also provides a preparation method of the above agricultural composition containing composite chitosan, which comprises the following steps: S1. Preparation of the composite chitosan solution; Mix oligosaccharides with a molecular weight of 200 - 2000, oligosaccharides with a molecular weight of 2000 - 6000, and polysaccharides with a molecular weight of 6000 - 100000 at 20 °C and then dissolve them in distilled water to obtain the composite chitosan solution; S2. Preparation of the composite carboxymethyl chitosan; Add 70 g of a sodium hydroxide solution with a mass fraction of 80% and 0.04 g of sodium dodecyl sulfate to 10 g of the composite chitosan solution, stir well, then let it stand at 4 °C for 1 h, and then freeze it overnight at -20 °C. Then add 196 mL of isopropanol and 30 g of monochloroacetic acid thereto while stirring. Then add 0.2 g of sodium borohydride, and react in a constant temperature water bath at 25 °C for 3 h. After the reaction is completed, filter to obtain a solid substance. Wash the solid substance with an ethanol solution with a volume fraction of 80%, place it in distilled water, adjust the pH of the solution to 7.0, filter to obtain a clear liquid, then ultrafilter it with a cut-off molecular weight of 8000 D, and then precipitate with acetone. Centrifuge the precipitate at 500 rpm and freeze-dry it at -4 °C for 30 min to obtain the composite carboxymethyl chitosan, where the density of the sodium hydroxide solution with a mass fraction of 80% is 1.43 g / cm 3 ; S3. Preparation of the composite carboxymethyl chitosan hydrogel; Dissolve ferric chloride in distilled water to prepare a ferric chloride solution with a mass fraction of 3%, dissolve calcium chloride solid in distilled water to prepare a calcium chloride solution with a mass fraction of 3%, and mix the ferric chloride solution and the calcium chloride solution according to a mass ratio of 1:2 to obtain a mixed ionic solution; Dissolve the composite carboxymethyl chitin in distilled water to prepare a composite carboxymethyl chitin solution with a mass fraction of 5%; Gradually add 40 mL of the composite carboxymethyl chitin solution dropwise to 50 mL of the mixed ionic solution, let it stand for 60 min, separate the lower layer substance, wash it with deionized water, and then dry it at 40 °C for 24 h to obtain the composite carboxymethyl chitin hydrogel; S4. Preparation of the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; Prepare oxidized hyaluronic acid by the sodium periodate oxidation method, and the specific method is the same as that in Example 1; Weigh 40 mg of the composite carboxymethyl chitin hydrogel and 40 mg of oxidized hyaluronic acid and dissolve them in 1 mL of ultrapure water respectively to prepare solutions. Then mix the two solutions in equal volume and add 20 mL of a DL-malic acid aqueous solution with a concentration of 1 mg / L. Let it stand for 60 min, then separate the lower layer substance, wash it with deionized water, and then dry it at 40 °C for 24 h to obtain the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; S5. Place 20 g of riboflavin in 140 mL of a 9 g / L sodium chloride solution, stir it in a water bath at 60 °C until completely dissolved. Dissolve 50 g of the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in 55 mL of deionized water, then add 35 g of the composite chitin solution to it. Slowly drip the riboflavin sodium chloride solution into it, and stir magnetically while adding at 900 rpm. After dripping, continue to stir for 20 minutes, and then perform homogenization treatment at 20 MPa for 30 min.

[0031] Comparative Example 1 This comparative example provides an agricultural composition containing composite chitin and its preparation method. The components and preparation method of this agricultural composition are the same as those in Example 1, except that in the preparation process of the composite carboxymethyl chitin hydrogel, the ferric chloride solution and the calcium chloride solution in the mixed ionic solution are mixed according to a mass ratio of 1:1.

[0032] Comparative Example 2 This comparative example provides an agricultural composition containing composite chitin and its preparation method. The components and preparation method of this agricultural composition are the same as those in Example 1, except that in the preparation process of the composite carboxymethyl chitin hydrogel, the ferric chloride solution and the calcium chloride solution in the mixed ionic solution are mixed according to a mass ratio of 2:1.

[0033] Comparative Example 3 This comparative example provides an agricultural composition containing composite chitin and a preparation method thereof. By weight, it includes the following components: 30 parts of composite chitin solution, 45 parts of DL-malic acid, and 15 parts of riboflavin.

[0034] 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 water bath at 60 °C until completely dissolved. 30 g of composite chitin solution and 45 g of DL-malic acid were added to 50 mL of deionized water, and the riboflavin sodium chloride solution was slowly dropped into it. While adding, magnetic stirring was carried out at 800 rpm. After the addition was completed, stirring was continued for 20 minutes, and then homogenization treatment was carried out at 20 MPa for 30 min.

[0035] Comparative Example 4 This comparative example provides an agricultural composition containing composite chitin and a preparation method thereof. By weight, it includes the following components: 30 parts of composite chitin solution, 45 parts of composite carboxymethyl chitin hydrogel loaded with DL-malic acid, and 15 parts of riboflavin.

[0036] Among them, the preparation method of the composite carboxymethyl chitin hydrogel loaded with DL-malic acid is: 40 mL of composite carboxymethyl chitin solution was slowly added dropwise to 50 mL of mixed ionic solution, then 20 mL of DL-malic acid aqueous solution with a concentration of 1 mg / mL was added, and left standing for 60 min. The lower layer substance was separated and washed with deionized water, and then dried at 40 °C for 24 h to obtain the composite carboxymethyl chitin hydrogel loaded with DL-malic acid.

[0037] Comparative Example 5 This comparative example provides an agricultural composition containing composite chitin and a preparation method thereof. By weight, it includes the following components: 45 parts of double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid, and 15 parts of riboflavin.

[0038] Grape fruits and tomato fruits from the same planting base were selected as the experimental models. First, the dust and impurities on the outer surfaces of the grape fruits and tomato fruits were gently rinsed with deionized water. After rinsing, the fruits were placed at room temperature and dried naturally in the dark. Then, the grape fruits and tomato fruits were divided into six groups, with 3 portions in each group, namely the Experimental Example 1 group and the Comparative Example 1-5 groups. The agricultural compositions prepared in Experimental Example 1 and Comparative Example 1-5 were respectively sprayed on the six groups of models using a small spray device. Spraying was carried out at a concentration of 20 mg / mL for 5 mL. The three portions in each group were respectively sprayed with deionized water at a flow rate of 15 mL / min at an angle of 45° 20 cm above the fruit surface at 0 h, 24 h, and 48 h after spraying the agricultural composition to simulate the rainwashing behavior, and each group was rainwashed for 45 min.

[0039] Then, 0.5 g of the fruits of each group of models was added to 10 mL of phosphate buffered saline, and then sonicated at 2 MHz for 1 min to completely release DL-malic acid. Then, it was 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 Table 1 and Table 2.

[0040] Table 1 Content results of DL-malic acid in six groups of grape models

[0041] Table 2 Content results of DL-malic acid in six groups of tomato models

[0042] As can be seen from Table 1 and Table 2, the content of the agricultural composition left on the fruits in the Example 1 group, Comparative Example 1 group, and Comparative Example 2 group at 0 h, 24 h, and 48 h was higher than that in the Comparative Example 3-4 groups, indicating that the double-crosslinked composite carboxymethyl chitosan hydrogel in the present invention has high adhesion to the surface of fruits and vegetables, can reduce or avoid being washed away by rain after use, will not affect the drug efficacy when used in rainy days, and comparing the experimental results of Comparative Example 3 and Comparative Example 4 shows that the composite carboxymethyl chitosan 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 chitosan hydrogel in the present invention.

[0043] Six groups of plants in the experimental vineyard were randomly selected, with 8 plants in each group, and a fruit growth and development experiment was carried out. At 3 weeks after flowering, all six groups of plants were sprayed with 5 mL at a concentration of 20 mg / mL, and the remaining conditions were carried out according to the actual situation. After the fruits were mature, the gram weight of grape berries and the berry coloration degree were measured. After the fruits were picked, they were all stored in the same environment, and the storage temperature was normal temperature 25 °C. The time when rot and lesion occurred on the fruit surface was recorded. The results are shown in Table 3.

[0044] Table 3 Results of berry gram weight, berry coloration degree and storage time of fruits of six groups of plants

[0045] As can be seen from Table 3, the average weight per grain and fruit coloration degree of the fruits obtained in the Example 1 group are both higher than those in the Comparative Example 1-2 groups. This is because the oxygen permeability of the double-crosslinked composite carboxymethyl chitosan hydrogel prepared from the mixed ionic solution obtained by mixing ferric chloride solution and calcium chloride solution in a mass ratio of 1:2 in the present invention is higher, which is beneficial to the growth and development of fruits. The storage time of the fruits in the Example 1 group and the Comparative Example 1-2 groups is higher than that in the Comparative Example 3 group and the Comparative Example 5 group, and the storage time of the Comparative Example 5 group is greater than that of the Comparative Example 3 group. This is because after the double-crosslinked composite carboxymethyl chitosan hydrogel of the present invention is completely dehydrated, a protective film will be formed on the surface of the fruits during the storage of the fruits. At the same time, under the action of the composite chitin, the permeation of oxygen is blocked, the permeation rate of carbon dioxide is increased, the respiration of the fruits during storage is reduced, and the composite chitin can prevent bacteria from invading the fruits.

[0046] The specific embodiments of the present invention described above do not limit the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An agricultural composition containing composite chitin, characterized in that, By weight, it includes the following components: 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, the composite carboxymethyl chitin hydrogel is obtained through ionic crosslinking, and then the composite carboxymethyl chitin hydrogel is crosslinked with oxidized hyaluronic acid and loaded with DL-malic acid.

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

3. The preparation method of the agricultural composition containing composite chitin according to claim 1, characterized in that, It includes the following steps: S1. Using the composite chitin solution as a raw material to prepare composite carboxymethyl chitin, then configuring the composite carboxymethyl chitin into a composite carboxymethyl chitin solution, slowly dropping the composite carboxymethyl chitin solution into a mixed ionic solution of ferric chloride and calcium chloride, standing and separating the lower layer substance, washing and drying to obtain the composite carboxymethyl chitin hydrogel; S2. Preparing the composite carboxymethyl chitin hydrogel and oxidized hyaluronic acid into solutions respectively, mixing the two solutions in equal volume, adding an aqueous solution of DL-malic acid, standing and separating the lower layer substance, washing and drying to obtain the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid; S3. Placing riboflavin in a 9 g / L sodium chloride solution, stirring in a water bath at 60 °C until completely dissolved to obtain a sodium chloride solution of riboflavin, dissolving the double-crosslinked composite carboxymethyl chitin hydrogel loaded with DL-malic acid in deionized water, then adding the composite chitin solution thereto, and slowly dropping the sodium chloride solution of riboflavin into it, magnetically stirring while adding under the condition of 800 to 1000 rpm, continuing to stir for 20 minutes after dropping, and then performing homogenization treatment at 20 MPa for 30 min to obtain the agricultural composition.

4. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, In step S2, the preparation method of the mixed ionic solution of ferric chloride and calcium chloride is as follows: dissolving ferric chloride and calcium chloride in distilled water respectively, configuring 3% mass fraction ferric chloride solution and calcium chloride solution respectively, and then mixing the ferric chloride solution and calcium chloride solution according to a mass ratio of 1:

2.

5. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, In step S2, the mass fraction of the composite carboxymethyl chitin solution is 5%.

6. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, In step S2, the volume ratio of the composite carboxymethyl chitin solution to the mixed ionic solution of ferric chloride and calcium chloride is 1 to 3:5, and the standing time is 60 min.

7. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, In step S3, the oxidized hyaluronic acid is prepared by the sodium periodate oxidation method.

8. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, The composite chitin is obtained by mixing 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 20 °C to 80 °C and then dissolving them in distilled water.

9. The preparation method of the agricultural composition containing composite chitin according to claim 3, characterized in that, The preparation method of the composite carboxymethyl chitin is as follows: Add a sodium hydroxide solution with a mass fraction of 80% and sodium dodecyl sulfate to the composite chitin solution. After stirring evenly, let it stand at 4 °C for 1 h, and freeze overnight to obtain a mixed solution; Add isopropanol, monochloroacetic acid, and sodium borohydride to the mixed solution, and stir and react in a constant temperature water bath at 25 °C for 3 h. After the reaction is completed, filter to obtain a solid substance. Wash the solid substance with an ethanol solution with a volume fraction of 80%, place it in distilled water, adjust the pH of the solution to 7.0, filter to obtain a clear liquid, then ultrafilter, and then precipitate with acetone. The precipitate obtained after centrifugal separation is freeze-dried to obtain the composite carboxymethyl chitin.

10. The preparation method of the agricultural composition containing composite chitin according to claim 9, characterized in that, The mass of the sodium dodecyl sulfate is 0.4% of the mass of the composite chitin solution, and the mass ratio of the sodium hydroxide solution to the composite chitin solution is 7:1; the addition amount of the isopropanol is 4 times the volume of the sodium hydroxide, and the mass ratio of the monochloroacetic acid to the composite chitin solution is 3:1.

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