Carboxymethyl porous chestnut starch, and preparation method and application thereof

Abstract

The present application relates to the technical field of drug carrier materials, and specifically discloses carboxymethyl porous chestnut starch as well as a preparation method and application thereof. The present application uniformly mixes chestnut starch with a weak acid buffer to obtain chestnut starch milk; a compound enzyme is added to the chestnut starch milk for enzymolysis to obtain porous chestnut starch; the compound enzyme comprises mesophilic alpha-amylase and isoamylase; the porous chestnut starch is added to an alcohol solution and uniformly mixed to obtain porous chestnut starch milk; after alkalinization by adding a first preset amount of strong alkali, an etherifying agent and a second preset amount of strong alkali are added to the porous chestnut starch milk to perform a carboxymethylation reaction, thereby obtaining carboxymethyl porous chestnut starch. The carboxymethyl porous chestnut starch and sodium alginate are combined, which not only can improve the loading capacity of amoxicillin drugs, but also can achieve the purpose of controlled release of amoxicillin, thereby providing a new idea for the preparation of amoxicillin controlled release preparations.

Description

Technical Field

[0001] This invention relates to the field of drug carrier materials technology, and in particular to a carboxymethyl porous chestnut starch, its preparation method, and its application. Background Technology

[0002] Amoxicillin (α-aminohydroxybenzylpenicillin) is a semi-synthetic, orally absorbed β-lactam broad-spectrum antibiotic with a short half-life (61.3 min). It is commonly used to treat bacterial infections, especially Helicobacter pylori. Common oral amoxicillin formulations have a short residence time in the stomach, and their structure is unstable and easily destroyed below their isoelectric point (pH 4.8), preventing them from reaching the infection site at an effective concentration for an extended period. While frequent high-dose dosing is often used to address this issue, it can cause gastrointestinal irritation, nausea, abdominal pain, and other adverse reactions, reducing patient compliance. Therefore, developing sustained-release amoxicillin formulations to maintain therapeutic blood concentrations for a longer period and thus improve drug utilization is of great significance.

[0003] Currently, sustained-release carrier materials include natural polymers, blended polymers, and fully synthetic polymers. Among them, natural polymers, such as starch, have advantages such as being green, inexpensive, and biodegradable, and are widely used in drug carriers. Starch raw materials are currently mostly corn, potatoes, wheat, and rice. Chestnuts, as a characteristic agricultural product of my country, are one of the world's famous dried fruits and are known as a "staple crop." Due to their high water content and poor storage properties, a large number of chestnuts are lost annually due to spoilage and mold, resulting in significant economic losses. To address this issue, we hope to improve the situation by reusing waste chestnut resources. However, chestnut starch has undesirable properties such as excessive viscosity after heating, insolubility in cold water, and easy decomposition, which greatly limit its application. Therefore, modifying chestnut starch to improve its application value in the production of sustained-release drugs is crucial. Summary of the Invention

[0004] To address the limitations of existing chestnut starch applications in the field of drug carriers, this invention provides a carboxymethyl porous chestnut starch, its preparation method, and its applications.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0006] A method for preparing carboxymethyl porous chestnut starch includes the following steps:

[0007] Step a: Mix chestnut starch with a weakly acidic buffer solution until homogeneous to obtain chestnut starch slurry; add a complex enzyme to the chestnut starch slurry for enzymatic hydrolysis to obtain porous chestnut starch; wherein, the complex enzyme includes mesophilic α-amylase and isoamylase;

[0008] Step b: Add the porous chestnut starch to an alcohol solution and mix evenly to obtain a porous chestnut starch emulsion; add a first preset amount of strong alkali to the porous chestnut starch emulsion for alkalization, then add an etherifying agent and a second preset amount of strong alkali to carry out a carboxymethylation reaction to obtain carboxymethyl porous chestnut starch.

[0009] Compared to existing technologies, the method for preparing carboxymethyl porous chestnut starch provided by this invention employs a specific complex enzyme to enzymatically hydrolyze chestnut starch, disrupting the amorphous regions composed of amylose and other components of the chestnut starch granules. Simultaneously, numerous small pores are formed on the surface, extending into the center of the starch, thereby disrupting some crystalline regions and exposing a large number of amorphous areas. This promotes effective collisions between starch molecules and the etherifying agent, increasing the degree of carboxymethyl substitution in the starch. Furthermore, during the carboxymethyl etherification modification reaction, the strong alkali acting on the porous starch surface further collapses the overall starch structure, exposing… Exposing more amorphous reaction sites composed of amylose further increases the degree of carboxymethyl substitution in starch. That is, the hydroxyl groups of monoglucose in porous chestnut starch are largely replaced by carboxymethyl groups, significantly increasing the negative charge of porous chestnut starch. This makes it easier to encapsulate positively charged drugs, such as amoxicillin. At the same time, the large number of carboxymethyl groups in carboxymethyl porous chestnut starch, as well as other active functional groups obtained by enzymatic hydrolysis, can interact strongly with the amide ring, acyl group, carboxyl group, and other groups of amoxicillin, which plays an important role in improving the loading capacity and loading stability of amoxicillin.

[0010] In one specific embodiment of the present invention, step a includes the following steps in the preparation method of chestnut starch:

[0011] Add the original chestnut starch to 4-6 times its volume of petroleum ether, stir for 1 hour, and centrifuge at 3500-4500 rpm to remove the fat from the chestnut starch. Add 4-6 times its volume of anhydrous ethanol to the precipitate obtained by centrifugation, stir for 0.5-1 hour, and centrifuge at 3500-4500 rpm. Repeat this process three times. Then add 4-6 times its volume of 0.15%-0.25% sodium hydroxide solution to the precipitate obtained by centrifugation, stir for 0.5-1 hour, and centrifuge at 3500-4500 rpm. Repeat this process three times. Finally, freeze-dry the precipitate obtained by centrifugation to obtain chestnut starch.

[0012] Further, in step a, the weakly acidic buffer solution is a citrate-disodium hydrogen phosphate buffer solution with a pH of 6.0 to 6.5.

[0013] Further, in step a, the mass concentration of the chestnut starch milk is 18% to 20%.

[0014] Furthermore, in step a, before adding the compound enzyme, the chestnut starch milk is preheated to 45℃~50℃.

[0015] Further, in step a, the mass ratio of the mesophilic α-amylase to the isoamylase is 1.8:3 to 2.2:3, and the amount of the compound enzyme added is 1190 U / g to 1278 U / g.

[0016] The selected compound enzyme can effectively destroy both the non-crystalline and crystalline regions of chestnut starch, allowing the chestnut starch to fully react with the etherifying agent, increasing the degree of carboxymethyl substitution in the starch, thus ensuring the subsequent large-scale encapsulation of amoxicillin. At the same time, it can also effectively shorten the enzymatic hydrolysis time and improve the hydrolysis efficiency.

[0017] Furthermore, in step a, the enzymatic hydrolysis temperature is 45℃~50℃, and the enzymatic hydrolysis time is 6h~7h.

[0018] Further, in step a, after the enzymatic hydrolysis is completed, anhydrous ethanol is added to inactivate the reaction, and then the mixture is centrifuged at 3500-4500 rpm for 3-5 times with distilled water and freeze-dried to obtain porous chestnut starch.

[0019] The preferred reaction conditions described above can promote the destruction of both the amorphous and crystalline regions of chestnut starch by the complex enzyme, thereby exposing more reaction sites and increasing the degree of carboxymethyl substitution in the subsequent starch reaction.

[0020] Further, in step b, the alcohol solution is an ethanol solution with a mass concentration of 80% to 90%.

[0021] Furthermore, in step b, the mass concentration of the porous chestnut starch milk is 6% to 14%.

[0022] Furthermore, in step b, before adding the strong alkali, the porous chestnut starch milk is preheated to 25°C to 30°C.

[0023] Furthermore, in step b, the strong base is sodium hydroxide.

[0024] Further, in step b, the porous chestnut starch, calculated as monoglucose, has a molar ratio of the first preset amount of strong alkali to porous chestnut starch of 1.50:1 to 2.25:1.

[0025] Furthermore, in step b, the alkalization temperature is 25℃~30℃, and the alkalization time is 30min~60min.

[0026] Further, in step b, the porous chestnut starch, calculated as monoglucose, has a molar ratio of the second preset amount of strong alkali to porous chestnut starch of 0.50:1 to 0.75:1.

[0027] Further, in step b, the etherifying agent is sodium chloroacetate or monochloroacetic acid.

[0028] Further, in step b, the molar ratio of the etherifying agent to chestnut starch, calculated as chestnut starch and monoglucose, is 2.75:1 to 3.5:1.

[0029] Furthermore, in step b, the temperature of the carboxymethylation reaction is 40℃~45℃, and the reaction time is 3h~4h.

[0030] The above-mentioned preferred reaction conditions can promote the full progress of the carboxymethylation reaction and increase the degree of substitution of starch carboxymethyl groups.

[0031] Furthermore, in step b, after the carboxymethylation reaction is completed, the reaction solution is adjusted to pH 6.5-7.0, washed with alcohol solution until chloride ions are removed, and dried to obtain carboxymethyl porous chestnut starch.

[0032] The present invention also provides a carboxymethyl porous chestnut starch, which is prepared by any of the above-mentioned methods for preparing carboxymethyl porous chestnut starch.

[0033] This invention also provides the application of the above-mentioned carboxymethyl porous chestnut starch in the preparation of amoxicillin sustained-release formulations.

[0034] The present invention also provides an amoxicillin sustained-release formulation, wherein the sustained-release carriers are carboxymethyl porous chestnut starch and sodium alginate.

[0035] Sodium alginate possesses good encapsulation and gelling properties; however, as a sustained-release material, sodium alginate alone has a loose overall structure, and the mechanical and barrier properties of the calcification film it forms with calcium ions are still poor, making the encapsulated material prone to leakage. Furthermore, it is prone to burst release under alkaline conditions, failing to achieve a long-term sustained-release effect under alkaline conditions. Currently, carboxymethyl starch alone cannot achieve a large-scale encapsulation of amoxicillin, and when combined with other biomass as a sustained-release material, it generally requires several hours or longer to achieve complete drug release. If it is directly used as a sustained-release carrier for amoxicillin, sufficient amoxicillin release during treatment cannot be guaranteed, reducing drug utilization.

[0036] This invention combines carboxymethyl porous chestnut starch and sodium alginate, which not only increases the loading capacity of amoxicillin but also achieves the purpose of sustained-release and controlled-release of amoxicillin, providing a new approach for the preparation of sustained-release and controlled-release formulations of amoxicillin.

[0037] Specifically, the amoxicillin sustained-release formulation is amoxicillin drug-loaded gel microspheres.

[0038] The carboxymethyl porous chestnut starch provided by this invention contains a large number of carboxymethyl groups in its overall structure. Under acidic conditions, the carboxymethyl groups are protonated, making the overall structure of the gel microspheres compact, which makes it difficult for amoxicillin to dissolve and inhibits its release. Under alkaline conditions, a large number of carboxymethyl groups in the structure of the gel microspheres are deprotonated, and a large number of like charges repel each other, making the overall structure loose and facilitating the entry of external water molecules. This allows the amoxicillin to dissolve and release up to 86% within 9 hours, achieving the goal of inhibiting the release of amoxicillin in gastric juice, prolonging its residence time, and releasing a large amount of amoxicillin after entering the intestine. This effectively improves the effective utilization rate of amoxicillin and provides an excellent carrier material for the preparation of amoxicillin sustained-release drugs. At the same time, it realizes the application of chestnut starch in the field of pharmaceutical materials, solves the problem of chestnut starch resource waste, and has high practical value.

[0039] This invention also provides a method for preparing the above-mentioned amoxicillin-loaded gel microspheres, comprising the following steps:

[0040] The carboxymethyl porous chestnut starch and amoxicillin were added to an aqueous solution of sodium alginate to obtain a reaction solution; the reaction solution was stirred to obtain a gel; after defoaming, the gel was dropped into an aqueous solution of calcium chloride, allowed to stand, washed, and freeze-dried to obtain amoxicillin-loaded gel microspheres.

[0041] Furthermore, the reaction solution contains 2%–4% (w / v) carboxymethyl porous chestnut starch, 2%–4% (w / v) amoxicillin, and 0.5%–2.5% (w / v) sodium alginate.

[0042] Furthermore, the mass ratio of calcium chloride to sodium alginate is 1:2 to 2:1.

[0043] This invention utilizes sodium alginate and carboxymethyl porous chestnut starch, two natural polymers, to form a physical network interpenetrating structure for the physical encapsulation of amoxicillin. The carrier materials are non-toxic, safe, and environmentally friendly, while also meeting the requirement of good biocompatibility for pharmaceutical materials. Furthermore, the preparation method of amoxicillin-loaded gel microspheres provided by this invention is simple to operate, low in cost, and uses readily available raw materials, which is of great significance for expanding the application of chestnut starch in pharmaceutical materials. Attached Figure Description

[0044] Figure 1 This is the standard curve for the degree of substitution of carboxymethyl porous chestnut starch in this invention;

[0045] Figure 2Infrared spectra of chestnut starch (CNS-1), porous chestnut starch (P-CNS-1), and carboxymethyl porous chestnut starch (CM-PCNS1) prepared in Example 1 of this invention;

[0046] Figure 3 Chestnut starch (CNS-1) prepared in Example 1 of this invention ( Figure 3 (a) Porous chestnut starch (P-CNS-1) Figure 3 (b) and carboxymethyl porous chestnut starch (CM-PCNS1) Figure 3 (c) SEM image;

[0047] Figure 4 XRD patterns of chestnut starch (CNS-1), porous chestnut starch (P-CNS-1), and carboxymethyl porous chestnut starch (CM-PCNS1) prepared in Example 1 of this invention;

[0048] Figure 5 This is a comparison chart of the transmittance of various starch samples prepared in the embodiments and comparative examples of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0050] To better illustrate the present invention, further examples are provided below.

[0051] Example 1

[0052] A method for preparing carboxymethyl porous chestnut starch (CM-PCNS-1):

[0053] Step 1: Add the original chestnut starch to 5 times its volume of petroleum ether, stir for 1 hour, and centrifuge at 4000 rpm to remove the fat from the chestnut starch; add 5 times its volume of anhydrous ethanol to the precipitate obtained by centrifugation, stir for 0.5 hours, and centrifuge at 4000 rpm. Repeat this process three times. Then add 5 times its volume of 0.2% sodium hydroxide solution to the precipitate obtained by centrifugation, stir for 0.5 hours, and centrifuge at 4000 rpm. Repeat this process three times. Finally, freeze-dry the precipitate obtained by centrifugation to obtain chestnut starch (CNS-1).

[0054] Step 2: The chestnut starch prepared above was added to a citrate-disodium hydrogen phosphate buffer solution at pH 6.2 to obtain a chestnut starch milk with a mass concentration of 19%. The chestnut starch milk was preheated at 48°C for 25 min, and then medium-temperature α-amylase and isoamylase were added in a mass ratio of 2:3. The amount of the combined enzyme added was 1232 U / g. The enzyme was hydrolyzed at 48°C for 6.5 h. Anhydrous ethanol was added to the reaction solution to inactivate the reaction. Then, the mixture was centrifuged 4 times at 4000 rpm with distilled water and freeze-dried to obtain porous chestnut starch (P-CNS-1).

[0055] Step 3: Add the prepared porous chestnut starch to an 85% (w / w) ethanol solution to obtain a 10% (w / w) porous chestnut starch slurry. Preheat the porous chestnut starch slurry at 28°C for 25 min, add 3 / 4 of the total sodium hydroxide, alkalize for 45 min, add sodium chloroacetate and the remaining 1 / 4 of the sodium hydroxide, react at 42°C for 3.5 h, adjust the pH to 6.8 with glacial acetic acid, and then wash with 85% ethanol solution until no Cl is visible. - (AgNO3 test was negative), and finally dried in an oven at 40℃ for 12h to obtain carboxymethyl porous chestnut starch (CM-PCNS-1); wherein, based on monoglucose, the molar ratio of total sodium hydroxide to porous chestnut starch was 2.5:1, and the molar ratio of sodium chloroacetate to porous chestnut starch was 3:1.

[0056] Example 2

[0057] A method for preparing carboxymethyl porous chestnut starch (CM-PCNS-2):

[0058] Step 1: Add the original chestnut starch to 4 times its volume of petroleum ether, stir for 1 hour, and centrifuge at 3500 rpm to remove the fat from the chestnut starch; add 4 times its volume of anhydrous ethanol to the precipitate obtained by centrifugation, stir for 1 hour, and centrifuge at 3500 rpm, repeating three times; then add 4 times its volume of 0.15% sodium hydroxide solution to the precipitate obtained by centrifugation, stir for 1 hour, and centrifuge at 3500 rpm, repeating three times; finally, freeze-dry the precipitate obtained by centrifugation to obtain chestnut starch (CNS-2);

[0059] Step 2: The chestnut starch prepared above was added to a citrate-disodium hydrogen phosphate buffer solution at pH 6.0 to obtain a chestnut starch milk with a mass concentration of 18%. The chestnut starch milk was preheated at 45°C for 20 min, and then medium-temperature α-amylase and isoamylase were added in a mass ratio of 1.8:3. The amount of the combined enzyme added was 1277.5 U / g. The enzyme was hydrolyzed at 45°C for 7 h. Anhydrous ethanol was added to the reaction solution to inactivate the reaction. Then, the mixture was centrifuged three times at 3500 rpm with distilled water and freeze-dried to obtain porous chestnut starch (P-CNS-2).

[0060] Step 3: Add the prepared porous chestnut starch to a 90% (w / w) ethanol solution to obtain a 14% (w / w) porous chestnut starch slurry. Preheat the porous chestnut starch slurry at 25°C for 20 min, add 3 / 4 of the total sodium hydroxide, alkalize for 30 min, add sodium chloroacetate and the remaining 1 / 4 of the sodium hydroxide, react at 45°C for 3 h, adjust the pH to 7.0 with glacial acetic acid, and then wash with 85% ethanol solution until no Cl is found. - (AgNO3 test was negative), and finally dried in an oven at 40℃ for 12h to obtain carboxymethyl porous chestnut starch (CM-PCNS-2); wherein, based on monoglucose, the molar ratio of total sodium hydroxide to porous chestnut starch was 3:1, and the molar ratio of sodium chloroacetate to porous chestnut starch was 2.75:1.

[0061] Example 3

[0062] A method for preparing carboxymethyl porous chestnut starch (CM-PCNS-3):

[0063] Step 1: Add the original chestnut starch to 6 times its volume of petroleum ether, stir for 1 hour, and centrifuge at 4500 rpm to remove the fat from the chestnut starch; add the precipitate obtained by centrifugation to 6 times its volume of anhydrous ethanol, stir for 1 hour, and centrifuge at 4500 rpm. Repeat this process three times. Then add the precipitate obtained by centrifugation to 6 times its volume of 0.25% sodium hydroxide solution, stir for 0.5 hours, and centrifuge at 4500 rpm. Repeat this process three times. Finally, freeze-dry the precipitate obtained by centrifugation to obtain chestnut starch (CNS-3).

[0064] Step 2: The chestnut starch prepared above was added to a citrate-disodium hydrogen phosphate buffer solution at pH 6.5 to obtain a chestnut starch milk with a mass concentration of 20%. The chestnut starch milk was preheated at 50°C for 30 min, and then medium-temperature α-amylase and isoamylase were added in a mass ratio of 2.2:3. The amount of the combined enzyme added was 1190 U / g. The enzyme was hydrolyzed at 50°C for 6 h. Anhydrous ethanol was added to the reaction solution to inactivate the reaction. Then, the mixture was centrifuged 5 times at 4500 rpm with distilled water and freeze-dried to obtain porous chestnut starch (P-CNS-3).

[0065] Step 3: Add the prepared porous chestnut starch to an 80% (w / w) ethanol solution to obtain a 6% (w / w) porous chestnut starch slurry. Preheat the porous chestnut starch slurry at 30°C for 30 min, add 3 / 4 of the total sodium hydroxide, alkalize for 60 min, add sodium chloroacetate and the remaining 1 / 4 of the sodium hydroxide, react at 40°C for 4 h, adjust the pH to 6.5 with glacial acetic acid, and then wash with 85% ethanol solution until no Cl- is detected. -(AgNO3 test was negative), and finally dried in an oven at 40℃ for 12h to obtain carboxymethyl porous chestnut starch (CM-PCNS-3); wherein, based on monoglucose, the molar ratio of total sodium hydroxide to porous chestnut starch was 2:1, and the molar ratio of sodium chloroacetate to porous chestnut starch was 3.50:1.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing carboxymethyl chestnut starch (CM-CNS), which specifically includes the following steps:

[0068] Step a: Chestnut starch was prepared according to step one of Example 1;

[0069] Step b: Add the chestnut starch prepared above to an 85% (w / w) ethanol solution to obtain a porous chestnut starch emulsion with a (w / w) concentration of 10%. Preheat the porous chestnut starch emulsion at 28°C for 25 min, add 3 / 4 of the total sodium hydroxide, alkalize for 45 min, add sodium chloroacetate and the remaining 1 / 4 of the sodium hydroxide, react at 42°C for 3.5 h, adjust the pH to 6.8 with glacial acetic acid, and then wash with 85% ethanol solution until no Cl is present. - (AgNO3 test was negative), and finally dried in an oven at 40℃ for 12 hours to obtain carboxymethyl porous chestnut starch (CM-CNS); wherein, based on monoglucose, the molar ratio of total sodium hydroxide to porous chestnut starch was 2.5:1, and the molar ratio of sodium chloroacetate to porous chestnut starch was 3:1.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing carboxymethyl porous corn starch (CM-PCS). The specific method is exactly the same as that in Example 1, except that chestnut starch in step one is replaced with corn starch.

[0072] Comparative Example 3

[0073] This comparative example provides a method for preparing carboxymethyl porous potato starch (CM-PPS), which is exactly the same as that in Example 1, except that the chestnut starch in step one is replaced with potato starch.

[0074] Comparative Example 4

[0075] This comparative example provides a method for preparing carboxymethyl porous wheat starch (CM-PWS), which is exactly the same as that in Example 1, except that chestnut starch in step one is replaced with wheat starch.

[0076] Comparative Example 5

[0077] This comparative example provides a method for preparing carboxymethyl porous rice starch (CM-PRS). The specific method is exactly the same as that in Example 1, except that the chestnut starch in step one is replaced with rice starch.

[0078] Degree of Substitution Determination

[0079] Degree of substitution (DS) is an important indicator for measuring the degree of carboxymethylation of starch. DS refers to the average number of hydroxyl groups that are substituted for each glucose unit in a starch molecule. Most glucose units in starch have three substituted hydroxyl groups; therefore, the maximum value of DS is 3. This experiment uses ultraviolet spectrophotometry. 0.1 g of the sample to be tested was accurately weighed and dissolved in 0.25 mol / L sodium hydroxide solution, then diluted to a volumetric flask with water to a final volume of 250 mL. A series of glycolic acid standard solutions (30, 60, 90, 120, 150 μg / mL) were prepared. 1 mL of each standard solution and sample solution was pipetted into a 25 mL volumetric flask. 0.5 mL of 1% J acid (6-amino-1-phenol-3-sulfonic acid) solution and 5 mL of concentrated sulfuric acid were added to each flask. The flasks were shaken well and heated in a boiling water bath for 1 hour. The solutions turned brownish-yellow. After the flasks cooled to room temperature, 30% ammonium acetate solution was added dropwise to the 25 mL mark. The solutions turned blue. Using the 30% ammonium acetate solution as a reference, the absorbance of each solution was measured at a wavelength of 620 nm. The degree of substitution was calculated using the following formula:

[0080]

[0081] In the above formula, B is the amount of glycolic acid in the carboxymethyl porous chestnut sample; 162: molar mass of the dehydrated glucose unit; 76: molar mass of glycolic acid; 58: CH2COO - The molar mass.

[0082] The standard curve of the degree of substitution of carboxymethyl pore chestnut starch is as follows: Figure 1 As shown in Table 1, the test results are as follows.

[0083] Table 2. Degree of Substitution for Each Starch Sample

[0084]

[0085]

[0086] As shown in Table 1, the carboxymethyl porous chestnut starch prepared in the embodiments of this invention has the highest degree of substitution, reaching 0.5160, which is significantly higher than that of other carboxymethyl porous starches. This invention achieves this by, on the one hand, using a specific complex enzyme hydrolysis reaction to destroy the amorphous regions of starch granules, such as amylose, and forming numerous small pores on their surface that extend to the center of the starch interior, thereby destroying some crystalline regions. This significantly increases the specific surface area of ​​the starch granules, exposing a large number of amorphous regions and promoting effective collisions between starch molecules and etherifying agents, thus increasing the degree of carboxymethyl substitution. On the other hand, during the carboxymethyl etherification modification reaction, the alkalizing agent (strong alkali) acts on the surface of the porous starch, causing further collapse of the overall structure and exposing more amorphous reaction sites composed of amylose, thereby increasing the degree of substitution. Therefore, considering both of these factors, the carboxymethyl porous chestnut starch prepared from chestnut starch has the highest degree of substitution. A high degree of substitution means that the hydroxyl groups in the monoglucose of porous chestnut starch are largely replaced by carboxymethyl groups, resulting in a strong overall negative charge on the material. Amoxicillin, on the other hand, is a zwitterionic drug, but its structure, consisting of an amide ring, an acyl group, and a carboxyl side chain, is generally acidic and positively charged. Therefore, the large number of carboxymethyl groups in carboxymethyl porous chestnut starch can generate strong charge interactions with the acidic groups in amoxicillin, providing a basis for the subsequent encapsulation and loading of amoxicillin, thereby increasing its dissolution and release.

[0087] FI-IR analysis

[0088] The infrared spectra of chestnut starch (CNS-1), porous chestnut starch (P-CNS-1), and carboxymethyl porous chestnut starch (CM-PCNS1) prepared in Example 1 of this invention are shown below. Figure 2 As shown.

[0089] Infrared results analysis, such as Figure 2 As shown, 3600~3000cm -1 This is the stretching vibration of the OH group in chestnut starch molecules, 2935 cm⁻¹. -1 The point represents the symmetrical stretching motion of -CH2, 1656cm -1 The peaks are related to the H2O molecule. Compared to chestnut starch, porous chestnut starch did not show any new functional group diffraction peaks, indicating that no chemical modification had occurred, only a change in the physical appearance structure; while carboxymethyl porous chestnut starch showed new functional group diffraction peaks, mainly manifested in the infrared curve of carboxymethyl porous chestnut starch at 1606 cm⁻¹. -1 1415cm -1 1331cm -1 A new absorption peak appears nearby, which is caused by the symmetric and asymmetric stretching motion of C=O, indirectly confirming the presence of -COO in chestnut starch molecules. - The introduction of this indicates the success of the etherification modification.

[0090] SEM analysis

[0091] Chestnut starch (CNS-1) prepared in Example 1 of this invention ( Figure 3 (a) Porous chestnut starch (P-CNS-1) Figure 3 (b) and carboxymethyl porous chestnut starch (CM-PCNS1) Figure 3 (c)SEM image as follows Figure 3 As shown.

[0092] As shown in the figure, chestnut starch (CNS-1) granules vary in size, have smooth surfaces without adhering substances, sharp edges, or cracks and depressions, and exhibit diverse shapes such as round, oval, pear-shaped, and polygonal. Enzymatically hydrolyzed porous chestnut starch (P-CNS-1) shows surface depressions and pores, with an increased specific surface area compared to regular chestnut starch. After etherification modification, porous etherified chestnut starch (CM-PCNS1) granules adhere to each other, exhibiting surface depressions, damage, and breakage. This is due to its unique layered structure, with the inner layer primarily consisting of relatively loose amorphous regions and the outer layer of tightly packed crystalline regions. During etherification, the interlayer bonding of chestnut starch weakens after alkalization, allowing the starch to swell and facilitating the entry of the etherifying agent. This damages the amorphous regions, creating lattice defects and reducing crystallinity. Meanwhile, the surface of chestnut starch was also corroded to a certain extent, causing the starch granules to stick together and break, which indirectly confirms that carboxymethyl groups were introduced into the porous chestnut starch molecules, thus confirming the success of the modification.

[0093] XRD analysis

[0094] The XRD patterns of chestnut starch (CNS-1), porous chestnut starch (P-CNS-1), and carboxymethyl porous chestnut starch (CM-PCNS1) prepared in Example 1 of this invention are shown below. Figure 4 As shown.

[0095] The diffraction peaks at 15.3°, 17.1°, and 23.1° in the figure are characteristic diffraction peaks of C-type crystalline starch. The diffraction peaks at 15.2° and 17.1° of the porous chestnut starch after enzymatic hydrolysis are weaker, which proves that enzymatic hydrolysis destroys part of the crystalline region. The diffraction peak at 23.1° is wider, indicating that enzymatic hydrolysis first destroys the amorphous region and then destroys the crystalline region to a limited extent. After etherification of porous chestnut starch, the diffraction peaks at 15.3°, 17.1°, and 23.1° disappeared, while a new diffraction peak appeared at 20.8°. This is likely due to the effect of the carboxymethyl group, which creates a new crystalline region. The original crystal form of chestnut starch is destroyed because the porous structure exposes both crystalline and amorphous regions, providing more reaction sites and facilitating the entry of the alkalizing agent sodium hydroxide. This intensifies the swelling of starch, which in turn facilitates the entry of the etherifying agent sodium chloroacetate. As a result, more hydroxyl groups in the starch are replaced by carboxymethyl groups. Due to the large steric hindrance of this group, the hydrogen bonding forces between starch molecules are greatly weakened, destroying the stable double helix structure of starch and ultimately forming an amorphous region, making its crystal form indistinct and mostly appearing as diffuse peaks.

[0096] Measurement of transmittance

[0097] Each sample was prepared into a 1% (w / w) starch emulsion using water. The emulsion was heated and stirred in a boiling water bath for 30 minutes while maintaining its original volume. The mixture was then cooled to room temperature to obtain the corresponding starch paste. The transmittance of each starch paste was measured at 620 nm using a 1 cm cuvette, with distilled water as a blank control. The data are shown in Table 2. Figure 5 As shown.

[0098] Table 2. Transmittance of various starch samples

[0099]

[0100] Porous chestnut starch has a higher transmittance than plain chestnut starch. Generally, after the formation of pores, the structural strength of the starch granules weakens under enzymatic action. Because the non-crystalline regions on the granule surface are hydrolyzed first, small pores are formed connecting the surface to the interior of the starch granules. Water molecules can easily penetrate the interior of the starch granules, leading to a more homogeneous hydration system and increased transmittance. Carboxymethyl chestnut starch (CM-CNS), obtained by direct etherification modification, has a higher transmittance than plain chestnut starch and porous chestnut starch. This is because the modified carboxymethyl chestnut starch introduces hydrophilic groups, improving the solubility of plain chestnut starch and thus facilitating light transmission. Furthermore, carboxymethyl porous chestnut starch obtained by etherification modification of porous chestnut starch has a higher transmittance than carboxymethyl chestnut starch, and transmittance is positively correlated with the degree of substitution. The highest transmittance of the prepared carboxymethyl porous chestnut starch can reach 69.80%. The transmittance of carboxymethyl porous starch prepared from corn, potato, wheat, and rice under the same conditions showed certain differences due to variations in the degree of substitution and particle size. The transmittances were 47.70%, 39.48%, 43.67%, and 36.34%, respectively. This is because, on the one hand, water molecules in the porous structure can easily penetrate into the starch granules, making it easier for the starch paste to form a homogeneous hydration system and increasing the transmittance. On the other hand, carboxymethyl porous chestnut starch has the highest degree of substitution, meaning that the number of hydroxyl groups on the glucose units of chestnut starch that are replaced by carboxymethyl groups is the largest, resulting in a greater degree of etherification, a greater number of introduced hydrophilic groups, stronger steric hindrance between molecules, larger intermolecular gaps, and significantly improved overall water solubility, thus significantly increasing the light transmittance.

[0101] Based on the significantly improved light transmittance, this property provides a uniformly cross-linked carrier material for the subsequent encapsulation of amoxicillin, ensuring uniform dispersion of the drug. Furthermore, after the drug-loaded material is transported to the intestinal therapeutic environment, the carrier itself dissolves due to its good water solubility, allowing a large amount of water molecules to enter, which facilitates the dissolution and release of amoxicillin in the intestinal environment. Moreover, the drug-loaded material is also biodegradable, achieving the research objective of ensuring the drug-loaded material is safe, non-toxic, green, and biodegradable. Therefore, the carboxymethyl porous chestnut starch prepared in this embodiment of the invention has the highest light transmittance, offering better performance advantages when used for the subsequent encapsulation and release of amoxicillin.

[0102] Application Examples

[0103] Blank gel microspheres and drug-loaded gel microspheres were prepared using chestnut starch (CNS-1) and porous chestnut starch (P-CNS-1) prepared in Example 1 and carboxymethyl porous chestnut starch (CM-PCNS-1, CM-PCNS-2, CM-PCNS-3) prepared in Examples 1 to 3, respectively.

[0104] 1. Preparation of blank gel microspheres:

[0105] Approximately 0.3 g of each starch sample was placed in 10 mL of 1% sodium alginate aqueous solution and magnetically stirred to form a network gel. The gel was then allowed to stand at room temperature to defoam. Subsequently, the gel was slowly dripped into 10 mL of 1% calcium chloride solution using a 1.2 mm outer diameter needle at room temperature. After standing to allow for full cross-linking, the gel was freeze-dried to obtain chestnut starch blank gel microspheres (SA / CNS), porous chestnut starch blank gel microspheres (SA / P-CNS), and carboxymethyl porous chestnut starch blank gel microspheres (SA / CM-PCNS).

[0106] 2. Preparation of drug-loaded gel microspheres:

[0107] Approximately 0.3 g of each starch sample and 0.3 g of amoxicillin were mixed thoroughly and placed in 10 mL of 1% sodium alginate aqueous solution. The mixture was magnetically stirred to form a network gel. After defoaming, the mixture was allowed to stand at room temperature. Then, at room temperature, the mixture was slowly dripped into 10 mL of 1% calcium chloride solution using a 1.2 mm outer diameter needle. After standing, the mixture was allowed to fully cross-link, and the free drug on the surface was washed off. The absorbance of the washing solution was measured using a UV spectrophotometer in a volumetric flask. The encapsulation efficiency and drug loading of the drug-loaded gel microspheres were calculated. Finally, the mixture was freeze-dried to obtain chestnut starch drug-loaded gel microspheres (SA / CNS / AMO), porous chestnut starch drug-loaded gel microspheres (SA / P-CNS / AMO), and carboxymethyl porous chestnut starch drug-loaded gel microspheres (SA / CM-PCNS-1 / AMO, SA / CM-PCNS-2 / AMO, SA / CM-PCNS-3 / AMO).

[0108] Following the same method as described above, the carboxymethyl porous starch samples prepared in Comparative Examples 2 to 5 were used to prepare drug-loaded gel microspheres, resulting in carboxymethyl porous corn starch drug-loaded gel microspheres (SA / CM-PCS / AMO), carboxymethyl porous potato starch drug-loaded gel microspheres (SA / CM-PPS / AMO), carboxymethyl porous wheat starch drug-loaded gel microspheres (SA / CM-PWS / AMO), and carboxymethyl porous rice starch drug-loaded gel microspheres (SA / CM-PRS / AMO). Simultaneously, commercially available carboxymethyl starch (DS = 0.3) was prepared into commercially available carboxymethyl starch drug-loaded gel microspheres (SA / CMS / AMO) using the same method as described above.

[0109] The formulas for encapsulation efficiency and drug loading are as follows. The results are shown in Table 3.

[0110]

[0111]

[0112] In the formula, M0 is the initial amount of amoxicillin added, in g; M1 is the amount of free amoxicillin, in g; and M2 is the mass of the drug-loaded gel microspheres, in g.

[0113] Table 3 Encapsulation efficiency and drug loading of drug-loaded gel microspheres

[0114]

[0115] As shown in Table 4, the encapsulation efficiency and drug loading of the modified chestnut starch drug-loaded gel microspheres were significantly higher than those of the unmodified chestnut starch drug-loaded gel microspheres. This is because, on the one hand, enzymatic modification promotes pore formation on the surface of chestnut starch and extends into the interior, increasing the specific surface area, which is beneficial for the encapsulation of amoxicillin; on the other hand, the combination of the carboxymethyl groups introduced by etherification modification and their electrostatic interaction with amoxicillin increases the encapsulation efficiency and drug loading of amoxicillin. Furthermore, the encapsulation efficiency and drug loading are directly proportional to the increase in the degree of carboxymethyl substitution. Carboxymethyl porous chestnut starch drug-loaded gel microspheres prepared from chestnut starch have a higher degree of carboxymethyl group substitution, resulting in a greater electrostatic interaction with amoxicillin. This leads to higher encapsulation efficiency and drug loading compared to carboxymethyl porous starch drug-loaded gel microspheres prepared from corn, potato, wheat, and rice, reaching up to 99.45% and 62.71%, respectively, providing a foundation for high in vitro amoxicillin release. In contrast, commercially available carboxymethyl starch drug-loaded gel microspheres have significantly lower encapsulation efficiency and drug loading than carboxymethyl porous chestnut starch drug-loaded gel microspheres. Because natural starch granules have a smaller specific surface area, the etherification reaction only occurs in the amorphous surface region, preventing the starch granules from penetrating and resulting in a lower degree of carboxymethyl group substitution. This reduces the amoxicillin loading, indirectly confirming the advantage of increasing specific surface area for the reaction to occur.

[0116] Determination of swelling ratio

[0117] The drug-loaded gel microsphere samples prepared above were placed in simulated gastric juice (SGF) at pH 1.2 and simulated intestinal juice (SCF) at pH 7.4 for swelling experiments. The samples were taken out and weighed at 0.5h, 1h, 2h, 3h, 4h, 6, 7h, 8h and 9h respectively. The swelling rate was calculated as follows, and the results are shown in Table 4.

[0118]

[0119] In the formula, W1 is the weight of the drug-loaded gel microspheres at time t, in g; W0 is the initial dry weight of the drug-loaded gel microspheres, in g.

[0120] Table 4. Swelling rates of drug-loaded gel microspheres at different pH values ​​at 9 hours.

[0121]

[0122]

[0123] Table 5 shows that the swelling rates of each sample reached equilibrium within 9 hours, and the swelling rate of carboxymethyl porous chestnut starch drug-loaded gel microspheres was higher than that of porous chestnut starch and chestnut starch drug-loaded gel microspheres. The swelling rate increased with increasing carboxymethyl substitution. Various carboxymethyl porous starch drug-loaded gel microspheres prepared from corn, potato, wheat, and rice generally had lower swelling rates under acidic and alkaline conditions than those from carboxymethyl porous chestnut starch drug-loaded gel microspheres. The highest swelling rate of carboxymethyl porous chestnut starch drug-loaded gel microspheres reached 473.12% under acidic conditions and 1591.71% under alkaline conditions. This is because carboxymethyl porous chestnut starch has the highest degree of substitution, with a large number of starch glucose units replaced by carboxymethyl groups. These carboxymethyl groups more easily form hydrogen bonds with water molecules, thus greatly improving the overall water solubility. Commercially available carboxymethyl starch, due to its small specific surface area, only undergoes modification in the amorphous regions on the surface of starch granules, resulting in minimal substitution of carboxymethyl groups and low swelling performance. In contrast, the carboxymethyl porous chestnut starch of this invention demonstrates the advantage of increased specific surface area due to pre-treatment with pores. Overall, the swelling rate under simulated gastric fluid conditions is significantly lower than that under simulated intestinal fluid conditions. Under acidic conditions, the carboxyl groups of sodium alginate and carboxymethyl porous starch are protonated, causing overall structural contraction and preventing water molecule entry, thus limiting the increase in swelling rate. However, under neutral or alkaline conditions, the carboxyl groups of the carrier material deprotonate, forming a large number of carboxylate ions. This generates a large number of like charges that repel each other, causing the internal cross-linked network structure to diffuse and loosen, facilitating water molecule entry and accelerating the dissolution and decomposition of the carrier material, thereby increasing the swelling rate and providing conditions for the subsequent large-scale dissolution and release of encapsulated amoxicillin.

[0124] Determination of cumulative drug release percentage M (%)

[0125] Using 10 mL of simulated gastric juice (SGF) at pH 1.2 and simulated colonic juice (SCF) at pH 7.4 as release media, 0.05 g of the prepared drug-loaded gel microsphere sample was accurately weighed and suspended at 100 r / min (37±0.5) °C for release. 2 mL of release medium was collected at 0.5 h, 1 h, 2 h, 3 h, 4 h, 6 h, 7 h, 8 h, and 9 h (with corresponding equal volumes of the same medium replenished at the same temperature). Each sample was measured in triplicate, and the cumulative drug release percentage M (%) was calculated using the formula. The results are shown in Table 5.

[0126]

[0127] In the formula, C i- The concentration of amoxicillin in the released solution at the i-th replacement (mg·L) -1 D-Amoxicillin loading (g·g) -1 );m drug - Mass of drug-loaded gel microspheres (g); n - Number of displacement media; V e -Volume of the release medium (L); V0 is the initial volume of the release liquid (L).

[0128] Table 5. Cumulative drug release rate of drug-loaded gel microspheres for various starch samples at different pH levels at 9 hours.

[0129]

[0130]

[0131] The experimental results in Table 6 show that, overall, the cumulative release rate of amoxicillin from the drug-loaded gel microspheres under acidic conditions was significantly lower than that under neutral and alkaline conditions within 9 hours. This is because under acidic conditions, the carboxymethyl groups of the drug-loaded gel microspheres are protonated, inhibiting the release of amoxicillin from the tightly packed structure. Conversely, under alkaline conditions, the carboxymethyl groups are deprotonated, leading to repulsion of like charges and a looser overall structure, which facilitates the large-scale dissolution and release of amoxicillin. This initially achieves inhibited release of amoxicillin in simulated gastric juice but a large-scale release in simulated intestinal tract. The release mechanism is based on the different swelling rates of the drug-loaded gel microspheres under different release media. Under acidic conditions, the release is mainly due to the release of surface-attached drug and diffusion, while under alkaline conditions, the release is partly due to the release of surface-attached drug and microsphere swelling, which facilitates drug diffusion. Another factor is the dissolution of the carrier material, leading to a large-scale release of amoxicillin encapsulated within the carrier material.

[0132] Among various carboxymethyl porous starch drug-loaded gel microspheres under the same conditions in this invention, the carboxymethyl porous chestnut starch drug-loaded gel microspheres have the highest degree of substitution. Due to the large number of carboxymethyl groups, a large amount of amoxicillin drug is loaded. The degree of protonation is high under acidic conditions and the degree of deprotonation is high under alkaline conditions. As a result, the amoxicillin drug release reduction is only 10.89% under acidic conditions, while the release can reach 86.72% under alkaline conditions. In contrast, commercially available carboxymethyl starch has a small specific surface area, so the modification only occurs in the amorphous region on the starch surface, which greatly reduces the substitution of carboxymethyl groups, thereby reducing the later loading of amoxicillin drug and thus reducing the later drug release. In comparison, the advantages of the carboxymethyl porous chestnut starch in this invention, which increases the specific surface area of ​​starch due to the early porous modification, are highlighted.

[0133] inhibition zone test

[0134] The activated and diluted concentration is approximately 1×10⁻⁶. 5 200 μL of CFU / mL *E. coli* and *Staphylococcus aureus* were evenly spread onto agar solid medium using a spreader and allowed to stand for absorption for approximately 10–20 min. Then, four blank gel microspheres and four drug-loaded gel microspheres prepared above were gently pressed onto the agar plate. For amoxicillin pure drug, the paper disc diffusion method was used: a 4 μg / mL 10 mL amoxicillin solution was prepared; 4 mm diameter paper discs were immersed in the amoxicillin solution for 10–20 min, then placed against the cup wall for 5–10 min, and finally spread evenly on the agar solid medium. The plates were then incubated upside down at 37°C for 24 h, and the size of the inhibition zone was observed. For comparison, the diameter of the inhibition zone for each sample was measured using a millimeter ruler. The antibacterial performance of the gel samples was evaluated using the inhibition zone diameter, calculated using the following formula. The results are shown in Table 6.

[0135] D′=Dd

[0136] In the formula: D′ is the diameter of the inhibition zone, mm; D is the outer diameter of the inhibition zone, mm; d is the diameter of the sample being tested, mm.

[0137] Table 6 Comparison of the antibacterial properties of each sample against Escherichia coli and Staphylococcus aureus

[0138]

[0139]

[0140]

[0141] The results showed that chestnut starch, porous chestnut starch, and carboxymethyl porous chestnut starch blank gel microspheres did not exhibit antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), indirectly indicating that the carrier materials were safe and non-toxic. The overall inhibitory diameter of the drug-loaded gel microspheres against E. coli and S. aureus was as follows: carboxymethyl porous chestnut starch 1-3-layer drug-loaded gel microspheres > carboxymethyl porous corn starch drug-loaded gel microspheres > carboxymethyl porous wheat starch drug-loaded gel microspheres > carboxymethyl porous potato starch drug-loaded gel microspheres > commercially available carboxymethyl starch drug-loaded gel microspheres > carboxymethyl porous rice starch drug-loaded gel microspheres > porous chestnut starch drug-loaded gel microspheres > chestnut starch drug-loaded gel microspheres > amoxicillin. Furthermore, the inhibitory sensitivity against Gram-positive Staphylococcus aureus was higher than that against Gram-negative Escherichia coli aureus. The reason for this trend is that when sodium alginate is added to chestnut starch and porous chestnut starch insoluble fillers, although it reduces the overall porosity of the gel microspheres to some extent and reduces the leakage of amoxicillin, it also occupies a large amount of the internal space of the gel microspheres, resulting in a significant decrease in the encapsulation rate of amoxicillin. This leads to a reduction in the amount of amoxicillin released in later applications, thereby reducing the antibacterial performance against Escherichia coli and Staphylococcus aureus, and resulting in a smaller inhibitory diameter. However, when sodium alginate is used in combination with carboxymethyl porous chestnut starch and various carboxymethyl porous starches prepared from corn, potatoes, wheat, rice, etc., network interpenetration ionization gel cross-linking occurs inside, forming a uniform network structure that effectively encapsulates amoxicillin and further prolongs the effective action time of amoxicillin. This is because the carboxymethyl porous chestnut starch drug-loaded gel... The microspheres exhibit the highest degree of substitution, with a large number of carboxymethyl groups substituted, resulting in a high degree of cross-linking with the sodium alginate network. This ensures uniform encapsulation of amoxicillin within the microspheres and significant electrostatic interactions with the amoxicillin, further increasing the amoxicillin loading. Consequently, the larger amount of amoxicillin released at the same timeframe leads to a greater inhibitory diameter against Escherichia coli and Staphylococcus aureus. This indirectly confirms that encapsulating amoxicillin in sodium alginate and carboxymethyl chestnut starch achieves a longer, slower release, effectively reducing the frequency of dosing. Furthermore, it ensures that the final release amount of amoxicillin reaches the level required for effective treatment, significantly improving drug utilization. This provides a foundation for addressing the current issues of prolonged release and low drug utilization in amoxicillin sustained-release formulations. Commercially available carboxymethyl starch has a small specific surface area, so the modification only occurs in a small part of the amorphous region, which greatly reduces the substitution of carboxymethyl groups, thereby reducing the load of amoxicillin in the later stage and thus reducing the release of the drug in the later stage, resulting in a small antibacterial diameter. In contrast, the advantages of the carboxymethyl porous chestnut starch in this invention, which increases the specific surface area of ​​starch due to the early porous modification, are highlighted.Furthermore, amoxicillin solution with a concentration of 4 μg / mL on the paper discs showed antibacterial properties against both E. coli and S. aureus, consistent with the minimum inhibitory concentration of amoxicillin against these two bacteria reported in relevant literature.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing carboxymethyl porous chestnut starch, characterized in that, Includes the following steps: Step a: Mix chestnut starch with a weakly acidic buffer solution until homogeneous to obtain chestnut starch slurry; add a complex enzyme to the chestnut starch slurry for enzymatic hydrolysis to obtain porous chestnut starch; wherein, the complex enzyme includes mesophilic α-amylase and isoamylase; Step b: Add the porous chestnut starch to an alcohol solution and mix evenly to obtain a porous chestnut starch emulsion; add a first preset amount of strong alkali to the porous chestnut starch emulsion for alkalization, then add an etherifying agent and a second preset amount of strong alkali to carry out a carboxymethylation reaction to obtain carboxymethyl porous chestnut starch.

2. The method for preparing carboxymethyl porous chestnut starch as described in claim 1, characterized in that, In step a, the weakly acidic buffer solution is a citrate-disodium hydrogen phosphate buffer solution with a pH of 6.0–6.5; and / or In step a, the mass concentration of the chestnut starch milk is 18%–20%; and / or In step a, the mass ratio of the mesophilic α-amylase to isoamylase is 1.8:3 to 2.2:3, and the amount of the complex enzyme added is 1190 U / g to 1278 U / g; and / or In step a, the enzymatic hydrolysis temperature is 45℃~50℃, and the enzymatic hydrolysis time is 6h~7h.

3. The method for preparing carboxymethyl porous chestnut starch as described in claim 1, characterized in that, In step b, the alcohol solution is an ethanol solution with a mass concentration of 80% to 90%; and / or In step b, the mass concentration of the porous chestnut starch milk is 6% to 14%; and / or In step b, the strong base is sodium hydroxide.

4. The method for preparing carboxymethyl porous chestnut starch as described in claim 1 or 3, characterized in that, In step b, the porous chestnut starch, calculated as monoglucose, has a molar ratio of the first preset amount of strong alkali to porous chestnut starch of 1.50:1 to 2.25:1; and / or In step b, the alkalization temperature is 25℃~30℃, and the alkalization time is 30min~60min; and / or In step b, the porous chestnut starch is calculated as monoglucose, and the molar ratio of the second preset amount of strong alkali to the porous chestnut starch is 0.50:1 to 0.75:

1.

5. The method for preparing carboxymethyl porous chestnut starch as described in claim 1, characterized in that, In step b, the etherifying agent is sodium chloroacetate or monochloroacetic acid; and / or In step b, the molar ratio of the etherifying agent to chestnut starch, calculated as chestnut starch and monoglucose, is 2.75:1 to 3.50:1; and / or In step b, the temperature of the carboxymethylation reaction is 40℃~45℃, and the reaction time is 3h~4h; and / or In step b, after the carboxymethylation reaction is completed, the reaction solution is adjusted to pH 6.5-7.0, washed with alcohol solution until chloride ions are removed, and dried to obtain carboxymethyl porous chestnut starch.

6. A carboxymethyl porous chestnut starch, characterized in that, It is prepared by the method for preparing carboxymethyl porous chestnut starch according to any one of claims 1 to 5.

7. The use of the carboxymethyl porous chestnut starch according to claim 6 in the preparation of amoxicillin sustained-release formulations.

8. An amoxicillin sustained-release formulation, characterized in that, Its sustained-release carrier includes the carboxymethyl porous chestnut starch and sodium alginate as described in claim 6.

9. The amoxicillin sustained-release formulation as described in claim 8, characterized in that, The amoxicillin sustained-release formulation is amoxicillin drug-loaded gel microspheres.

10. The method for preparing the amoxicillin sustained-release formulation according to claim 9, characterized in that, Includes the following steps: The carboxymethyl porous chestnut starch and amoxicillin were added to an aqueous sodium alginate solution and stirred to obtain a gel. After defoaming the gel, it was dropped into an aqueous calcium chloride solution, allowed to stand, washed, and freeze-dried to obtain amoxicillin-loaded gel microspheres.

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