Improved method for preparing composite modified starch by semi-dry method and application thereof

Abstract

The application provides a method for preparing a composite modified starch by an improved semi-dry method and application, and relates to the technical field of deep processing of starch. The method comprises the following steps: S1, raw material pretreatment: mixing starch raw material, solid alkali and calcium carbonate to obtain a mixture, adding anhydrous ethanol, and mixing at low temperature; then vacuumizing and filling nitrogen to obtain activated starch; S2, modification treatment: adding a modifier to perform microwave radiation assisted reaction: first performing one-stage microwave radiation at a power density of 7-8 kW / kg, then performing two-stage microwave radiation at a power density of 5-6 kW / kg, and finally performing three-stage microwave radiation at a power density of 3-4 kW / kg; and S3, post-treatment: vacuumizing after the reaction is completed, and cooling to 25 DEG C to obtain the product. The method has high production efficiency, low energy consumption, and conforms to the green manufacturing trend; the obtained product has high substitution degree, high viscosity, good product uniformity, and high solubility in cold water.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of starch deep processing, in particular to an improved semi-dry method for preparing composite modified starch and application thereof. BACKGROUND

[0002] Starch is a natural resource with wide sources, and has the characteristics of low price, renewable, biodegradable and no pollution. However, the ordinary natural starch does not have good processing performance, which limits the application of starch in modern technology. Therefore, people develop the modification technology of starch according to the structure and physical and chemical properties of starch, so that the starch has more excellent properties, is more widely applied, and has more outstanding effects, and new application fields are continuously developed through application research.

[0003] The semi-dry method is a production method for modified starch developed on the basis of the dry method process. However, the semi-dry method for producing modified starch (etherification, esterification, cationization modification) has the following problems: (1) the above modifications all need to be reacted at high temperature of 60-90℃ for a long time (4-24h), which has high energy consumption and low efficiency; (2) a large amount of organic solvent is used, and needs to be treated by neutralization, washing and other post-processing procedures, which has a complex process; (3) there are many side reactions, which leads to poor uniformity of the product, such as large difference in degree of substitution, viscosity and other differences between the same batch or different batches, large performance fluctuation, and influence on the application of modified starch product.

[0004] The existing research confirms that microwave can accelerate the activation of starch molecules, and the microwave technology has been applied in the modification treatment of cationization, esterification and etherification of starch. For example, patent CN101863994A discloses a method for preparing esterified starch by microwave, which is prepared by using acrylic acid, methacrylic acid, butenedioic acid, maleic anhydride, acetic acid, acetic anhydride, octenyl succinic anhydride, citric acid, phosphate as esterification agent, and reacting in a microwave oven under the catalysis of concentrated sulfuric acid, p-toluenesulfonic acid, sulfonic acid type strong acid cation exchange resin and tetra-chloro-aluminum ether complex. The esterified starch produced by using the microwave method has fast heating speed of microwave, can greatly reduce the reaction time, and improves the reaction efficiency, but the esterified starch produced by the method still has the problem of poor product uniformity. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides an improved semi-dry method for preparing composite modified starch and application thereof.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] According to an aspect of the present application, an improved semi-dry method for preparing composite modified starch comprises the following steps:

[0008] S1, raw material pretreatment: the starch raw material, solid alkali, calcium carbonate are mixed to obtain a mixture, ethanol is added, and low-temperature premixing is performed; then vacuum is extracted and nitrogen is filled to obtain activated starch;

[0009] S2, modification treatment: the modifier is added and uniformly mixed, and then microwave radiation assisted reaction is performed; the microwave radiation assisted reaction process is as follows: first, one-stage microwave radiation is performed at a power density of 7-8 kW / kg, then two-stage microwave radiation is performed at a power density of 5-6 kW / kg, and finally three-stage microwave radiation is performed at a power density of 3-4 kW / kg;

[0010] S3, post-treatment: after the reaction is completed, vacuum is extracted to remove residual covs, and cooling is performed to 25 DEG C.

[0011] Further, the starch raw material is selected from any one or a combination of corn starch, cassava starch and potato starch; the moisture content of the starch raw material is 10-15%.

[0012] Further, in step S1, the mass fraction of the ethanol is ≥90%, for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and the like; the amount of ethanol is 20-30% of the dry weight of the starch raw material.

[0013] In the present application, the moisture content of the starch raw material is 10-15%, the higher the moisture content, the greater the loss factor value, and the more significant the heating effect. Therefore, in the pretreatment process, ethanol with a mass fraction of ≥90% is selected, so as to control the moisture content in the pretreatment reaction system within a certain range, thereby ensuring good radiation heating effect, and also avoiding excessive water affecting the subsequent radiation effect, thereby helping to improve the performance of the product.

[0014] Further, the solid alkali is sodium hydroxide and / or potassium hydroxide; the amount of the solid alkali is 1-10% of the dry weight of the starch raw material.

[0015] Further, the amount of calcium carbonate is 5-15% of the dry weight of the starch raw material.

[0016] In the present application, calcium carbonate is added in the raw material pretreatment process, and the particle size is 300-500 mesh. The "ball bearing" effect of the granular calcium carbonate separates the raw material particles, avoids the caking of the raw material during the reaction, and the calcium carbonate hardly absorbs moisture, avoids the reduction of water content, thereby affecting the effect of the subsequent radiation heating treatment on the raw material, and helps to improve the performance of the product.

[0017] Further, in step S1, the low-temperature premixing conditions are as follows: the temperature is ≤25 DEG C, and the time is 10-30 min.

[0018] Further, in step S1, the vacuumizing and nitrogen filling process is to ensure an oxygen-free environment to prevent starch oxidation and viscosity reduction.

[0019] Further, in step S2, the modifier is an etherifying agent, an esterifying agent, or a cationizing agent; the amount of the modifier is 5-30% of the dry weight of the starch.

[0020] Optionally, the etherifying agent, the esterifying agent, and the cationizing agent are all conventional choices in the art and are not particularly limited; for example, the etherifying agent is chloroacetic acid or propylene oxide; the esterifying agent is a compound containing an anhydride group, which can be exemplified by acetic anhydride or octenyl succinic anhydride; and the cationizing agent is a quaternary ammonium salt cationizing agent, such as 3-chloro-2-hydroxypropyl trimethyl ammonium chloride.

[0021] Further, the modifier is pre-dissolved in ethanol (mass fraction ≥ 90%) before use, and the mass ratio of ethanol to the modifier is 1:1.

[0022] Further, in step S2, in the process of microwave-assisted reaction, the temperature is raised to 30-45℃ in the first stage, to 50-60℃ in the second stage, and to 70-85℃ in the third stage; the frequency is kept at 2450 MHz ± 50 MHz in the three stages; and the temperature is measured in real time by infrared.

[0023] The method of the present application uses segmented microwave radiation heating treatment, high power density is used in the initial stage to rapidly heat the reaction raw materials to 30-45℃, so as to promote the instantaneous uncoiling of the starch molecular helical structure, expose more hydroxyl groups, and activate the modification reaction; medium power density is used in the intermediate stage to heat to 50-60℃, so as to prevent overheating on the surface and ensure the reaction efficiency and uniformity; and low power density is used in the final stage to heat to 70-85℃ to enter the gelatinization zone, because the dielectric properties of the raw materials change greatly, which is prone to uneven heating, so low power density is used to prolong the action time and ensure the reaction degree. By precisely controlling the radiation power and temperature in each stage, the reaction time is shortened, the reaction efficiency is improved, the penetration rate of the modifier is improved, the conversion rate is improved, side reactions such as decomposition, carbonization, and polymerization of the target product caused by local overheating or temperature runaway are avoided, the purity and yield of the product are improved, the activity of the product is maximized, the degree of substitution of the modified starch product is improved, and the uniformity is improved.

[0024] Preferably, in the process of microwave-assisted reaction, after the completion of the first stage and the second stage of microwave radiation, the microwave radiation is paused for heat preservation.

[0025] After the first phase of microwave radiation is completed, the ratio of the time for pausing microwave radiation to the time for microwave radiation in the first phase (i.e., the pause / radiation time ratio) is (0.3~0.5):1;

[0026] After the second phase of microwave radiation is completed, the ratio of the time for stopping microwave radiation to the time for microwave radiation in the second phase is (1~2):1.

[0027] This application utilizes microwave radiation heating treatment, adding a pause step after the first and second stages of microwave radiation, and precisely controlling the pause / radiation time ratio. During radiation, microwave energy directly acts on polar molecules. For systems containing polar solvents or reactants, rapid heating can be achieved, significantly shortening the total exposure time of materials in high-temperature environments. The shorter the residence time of raw materials at the reaction temperature, the lower the probability of degradation. Heating stops instantaneously upon microwave radiation cessation, achieving rapid heating and cooling. This allows for selective energy provision to desired reaction pathways, suppressing side reactions with higher activation energies, reducing byproduct formation, and improving product purity from the source.

[0028] Because the duration of each microwave radiation session is affected not only by the power density and required temperature, but also by the amount of starch raw material used—a larger amount of starch raw material will result in a longer time—this study does not specify the exact duration of microwave radiation or the shutdown time, but only their proportional relationship. For example, if the starch raw material is 200g and its initial temperature is 25℃, and the temperature is raised to 45℃ at a power density of 8kW / kg in the first stage, the infrared monitoring time to reach that temperature is approximately 2 minutes. Based on a pause / radiation time ratio of (0.3–0.5):1, the pause time can be calculated to be 0.6–1 minutes.

[0029] Furthermore, in step S3, after cooling to 25°C, the product is purified according to the purity requirements. Purification can be achieved by adding ethanol for precipitation, centrifugation, washing, drying, and finally pulverizing.

[0030] Optionally, the washing is performed using an ethanol solution, preferably with a mass fraction of 70%.

[0031] Furthermore, the modified starch prepared using the above method has a coefficient of variation of substitution degree ≤6.5% and a solubility in cold water ≥90%.

[0032] According to another aspect of this application, an application is provided for the modified starch prepared by the above method, the application including the application of the modified starch in food, paper, textile materials or pharmaceutical materials.

[0033] Optionally, the modified starch of this application can be used in food to replace gelatin in the preparation of low-fat yogurt, improving the water-holding capacity of the product by 40%.

[0034] Optionally, the modified starch of this application can be used in paper production as a retention aid to improve the tensile strength of paper, with an improvement of up to 18% (cationically modified starch).

[0035] Optionally, the modified starch of this application can be used in the production of medical materials as a medical carrier material, shortening the film-forming time. The film-forming time of carboxymethyl starch is shortened to 3 seconds (compared to 12 seconds for traditional products).

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] 1. This application provides an improved semi-dry method for preparing composite modified starch. This method uses microwave-assisted semi-dry processing to produce modified starch, breaking through the traditional diffusion control mechanism of modifiers. It can complete a reaction that typically takes several hours in just a few minutes, significantly improving production efficiency and reducing energy consumption (achieving energy savings of over 40% compared to steam heating), aligning with the trend of green manufacturing. The resulting product has high substitution degree, high viscosity, good product uniformity, and high solubility in cold water.

[0038] 2. By adopting segmented microwave radiation and optimizing microwave radiation conditions, this application has achieved improved reaction efficiency while simultaneously increasing the degree of substitution, viscosity, and uniformity of the product. The standard deviation of the degree of substitution of modified starch produced in the same batch and different batches is ≤0.02.

[0039] 3. The modified starch produced by the method provided in this application can be used to produce low-fat yogurt, paper, and medical carrier materials. Attached Figure Description

[0040] Figure 1 This is the infrared spectrum of hydroxypropyl starch from Example 1 of this application. Detailed Implementation

[0041] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of this application, but do not limit this application in any way. The following content is merely an exemplary description of the scope of protection claimed in this application, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection claimed in this application.

[0042] The present application will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of this application are obtained through conventional commercial means.

[0043] Example 1

[0044] An improved semi-dry method for preparing composite modified starch, the specific steps of which are as follows:

[0045] S1. Raw material pretreatment: Corn starch (moisture content 15%), sodium hydroxide and calcium carbonate are mixed to obtain a mixture, ethanol (mass fraction 98%) is added, and the mixture is premixed at 15°C for 10 min; then vacuum is drawn and nitrogen is purged to obtain activated starch;

[0046] The amount of sodium hydroxide used is 10% of the dry weight of the starch raw material; the amount of calcium carbonate used is 5% of the dry weight of the starch raw material; and the amount of ethanol used is 10% of the dry weight of the starch raw material.

[0047] S2. Modification treatment: Add propylene oxide and mix well. The amount of propylene oxide is 5% of the dry weight of the starch raw material. Then, carry out microwave radiation-assisted reaction. The microwave radiation-assisted reaction process is as follows: first, microwave radiation is carried out at a power density of 7 kW / kg until the temperature reaches 30℃; then, the power density is reduced to 5 kW / kg for a second stage of microwave radiation until the temperature reaches 50℃; finally, the power density is reduced to 3 kW / kg for a third stage of microwave radiation until the temperature reaches 70℃. The frequency is maintained at 2450MHz±50 MHz throughout the microwave radiation process.

[0048] S3. Vacuum the product to remove residual COVS, cool to 25°C, and dry to obtain carboxymethylated starch. Depending on the purity requirements of the product, purify the product using the following steps: precipitate with ethanol, centrifuge, wash with 70% ethanol, and dry to obtain hydroxypropyl starch.

[0049] The product, hydroxypropyl starch, was subjected to infrared spectroscopy, and the results are as follows: Figure 1 As shown. It can be seen that 2970cm -1 The absorption peak for the stretching vibration of -CH is located at 1380 cm⁻¹. -1 The absorption peak at 1127 cm⁻¹ is the bending vibration absorption peak of -CH. -1 The peak at this point is the stretching vibration absorption peak of COC, indicating that the product is hydroxypropyl starch.

[0050] Example 2

[0051] An improved semi-dry method for preparing composite modified starch, the process flow diagram is as follows: Figure 1 As shown, the specific steps are as follows:

[0052] S1. Raw material pretreatment: Corn starch (moisture content 10%), sodium hydroxide and calcium carbonate are mixed to obtain a mixture, ethanol (mass fraction 90%) is added, and the mixture is premixed at 25°C for 20 min; then vacuum is drawn and nitrogen is purged to obtain activated starch;

[0053] The amount of sodium hydroxide used is 20% of the dry weight of the starch raw material; the amount of calcium carbonate used is 15% of the dry weight of the starch raw material; and the amount of ethanol used is 20% of the dry weight of the starch raw material.

[0054] S2. Modification treatment: Add chloroacetic acid and mix well. The amount of chloroacetic acid is 15% of the dry weight of the starch raw material. Then, carry out microwave radiation-assisted reaction. The microwave radiation-assisted reaction process is as follows: first, microwave radiation is carried out at a power density of 8 kW / kg until the temperature reaches 45℃; then, the power density is reduced to 6 kW / kg for a second stage of microwave radiation until the temperature reaches 60℃; finally, the power density is reduced to 4 kW / kg for a third stage of microwave radiation until the temperature reaches 85℃. The frequency is maintained at 2450MHz±50 MHz throughout the microwave radiation process.

[0055] S3. Post-processing: Vacuum is applied to remove residual COVS, and the mixture is cooled to 25°C and dried to obtain carboxymethylated starch.

[0056] Example 3

[0057] An improved semi-dry method for preparing composite modified starch, the process flow diagram is as follows: Figure 1 As shown, the specific steps are as follows:

[0058] S1. Raw material pretreatment: Cassava starch (moisture content 10%), sodium hydroxide and calcium carbonate are mixed to obtain a mixture, ethanol (mass fraction 90%) is added, and the mixture is premixed at 25°C for 20 min; then vacuum is drawn and nitrogen is purged to obtain activated starch;

[0059] The amount of sodium hydroxide used is 10% of the dry weight of the starch raw material; the amount of calcium carbonate used is 15% of the dry weight of the starch raw material; and the amount of ethanol used is 20% of the dry weight of the starch raw material.

[0060] S2. Modification treatment: Add acetic anhydride and mix well. The amount of acetic anhydride is 30% of the dry weight of the starch raw material. Then, carry out microwave radiation-assisted reaction. The microwave radiation-assisted reaction process is as follows: first, microwave radiation is carried out at a power density of 8 kW / kg until the temperature reaches 45℃; then, the power density is reduced to 6 kW / kg for a second stage of microwave radiation until the temperature reaches 60℃; finally, the power density is reduced to 4 kW / kg for a third stage of microwave radiation until the temperature reaches 85℃. The frequency is maintained at 2450MHz±50 MHz throughout the microwave radiation process.

[0061] S3. Post-processing: Cool to 25°C, add ethanol to precipitate, centrifuge, wash with 70% ethanol and dry to obtain acetylated starch.

[0062] Example 4

[0063] An improved semi-dry method for preparing composite modified starch, the process flow diagram is as follows: Figure 1 As shown, the specific steps are as follows:

[0064] S1. Raw material pretreatment: Potato starch (moisture content 15%), sodium hydroxide and calcium carbonate are mixed to obtain a mixture, ethanol (mass fraction 95%) is added, and the mixture is premixed at 10°C for 30 min; then vacuum is drawn and nitrogen is purged to obtain activated starch;

[0065] The amount of sodium hydroxide used is 10% of the dry weight of the starch raw material; the amount of calcium carbonate used is 15% of the dry weight of the starch raw material; and the amount of anhydrous ethanol used is 20% of the dry weight of the starch raw material.

[0066] S2. Modification treatment: Add 3-chloro-2-hydroxypropyltrimethylammonium chloride and mix well. The amount of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 30% of the dry weight of the starch raw material. Then, carry out a microwave-assisted reaction. The microwave-assisted reaction process is as follows: first, microwave radiation is carried out at a power density of 8 kW / kg until the temperature reaches 45℃; then, the power density is reduced to 6 kW / kg for a second stage of microwave radiation until the temperature reaches 60℃; finally, the power density is reduced to 4 kW / kg for a third stage of microwave radiation until the temperature reaches 85℃. The frequency is maintained at 2450MHz±50 MHz throughout the microwave radiation process.

[0067] S3. Post-processing: Cool to 25°C, add ethanol to precipitate, centrifuge, wash with 70% ethanol, and dry to obtain cationic modified starch.

[0068] Example 5

[0069] The difference from Example 2 is that the amount of calcium carbonate used is 20% of the dry weight of the starch raw material.

[0070] Example 6

[0071] The difference from Example 2 is that the microwave radiation reaction process is as follows: first, microwave radiation is carried out at a power density of 8 kW / kg until the temperature reaches 45°C, then microwave radiation is paused, with a pause / radiation time ratio of 0.5:1; then, the power density is reduced to 6 kW / kg for a second stage of microwave radiation until the temperature reaches 60°C, then microwave radiation is paused, with a pause / radiation time ratio of 2:1; finally, the power density is reduced to 4 kW / kg for a third stage of microwave radiation until the temperature reaches 85°C.

[0072] Example 7

[0073] The difference from Example 2 is that the microwave radiation reaction process is as follows: first, microwave radiation is carried out at a power density of 8 kW / kg until the temperature reaches 45°C, then microwave radiation is paused, with a pause / radiation time ratio of 0.3:1; then, the power density is reduced to 6 kW / kg for a second stage of microwave radiation until the temperature reaches 60°C, then microwave radiation is paused, with a pause / radiation time ratio of 1:1; finally, the power density is reduced to 4 kW / kg for a third stage of microwave radiation until the temperature reaches 85°C.

[0074] Example 8

[0075] The difference from Example 6 is that, during the microwave radiation reaction process, the ratio of pause / radiation time after the completion of the first stage of microwave radiation is 1:1, and the ratio of pause / radiation time after the completion of the second stage of microwave radiation is 3:1.

[0076] Example 9

[0077] The difference from Example 6 is that, during the microwave radiation reaction process, microwave radiation was not paused after the first stage of microwave radiation was completed, but the second stage of microwave radiation was carried out directly.

[0078] Comparative Example 1

[0079] The difference from Example 2 is that calcium carbonate was not added in step S1.

[0080] Comparative Example 2

[0081] The difference from Example 2 is that the microwave radiation-assisted reaction process is only one stage, and the microwave conditions are: microwave radiation is carried out at a power density of 6 kW / kg until the temperature reaches 85°C, and the frequency remains unchanged during the microwave radiation process.

[0082] Comparative Example 3

[0083] The difference from Example 3 is that no microwave radiation-assisted reaction was carried out during the modification reaction process, that is, the modification process was: reaction at 85°C for 120 min.

[0084] Experimental Example 1

[0085] The degree of substitution, viscosity, solubility in cold water at 4°C, and standard deviation of product DS and coefficient of variation of the modified starches prepared in the above examples and comparative examples were tested:

[0086] Degree of Substitution: The modified starches obtained in the above examples and comparative examples are of different types, and the test methods for the degree of substitution vary depending on the type of modified starch. Specifically, the acetyl content of acetylated starch was tested using the alkaline hydrolysis-acid-base titration method; the hydroxypropyl content of hydroxypropyl starch was tested using spectrophotometry (propylene glycol method); the carboxyl content of carboxymethyl starch was tested using the ashing-acid-base titration method; and the degree of substitution of cationic modified starch was determined by testing the nitrogen content using the Kjeldahl method and calculating the degree of substitution.

[0087] Viscosity: Using BROOKFIELD DV-II + The Pro viscometer was used for testing.

[0088] Standard deviation and coefficient of variation of product DS within a batch: Sampling was conducted in accordance with GB / T 6679-2003 "General Rules for Sampling of Solid Chemical Products", the degree of substitution of the products was tested, and the standard deviation and coefficient of variation were calculated.

[0089] The results are shown in Table 1 below.

[0090] Table 1 Properties of Modified Starch

[0091]

[0092] The results showed that the modified starches obtained in Examples 1-4 had high degrees of substitution, high viscosity, and high solubility in cold water. The batch-to-batch standard deviation of the dissolved solids (DS) and coefficient of variation were small, indicating good product uniformity. Compared to Example 2, Comparative Example 1, without the addition of calcium carbonate, showed a decrease in the degree of substitution, viscosity, and solubility in cold water. Example 5, with the addition of excess calcium carbonate, did not show a significant improvement in the degree of substitution or solubility in cold water compared to Comparative Example 1. This indicates that adding a certain amount of calcium carbonate to the reaction system helps to improve the degree of substitution, viscosity, and solubility in cold water of the product.

[0093] Compared to Example 2, Comparative Example 2 did not use segmented radiation, resulting in a decrease in the degree of substitution and viscosity of the obtained product. Furthermore, the standard deviation and coefficient of variation of the degree of substitution within the batch were high, indicating poor product stability. Comparative Example 3 maintained a conventional heating method, requiring a reaction time of 120 minutes to obtain a product with a DS of 0.26. This resulted in a long reaction time (the reaction time of all examples did not exceed 15 minutes), and a decrease in the degree of substitution and stability of the product.

[0094] In the microwave radiation reaction processes of Examples 5 and 6, radiation was paused for a certain period of time after the first and second stages of radiation were completed. The standard deviation of DS and the coefficient of variation of the resulting products were lower than those of Example 2. This indicates that adding a pause step in the segmented microwave radiation reaction process helps to improve the stability and uniformity of the product.

[0095] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope of this application should be within the protection scope of this application.

Claims

1. An improved semi-dry method for preparing composite modified starch, characterized in that, Includes the following steps: S1. Raw material pretreatment: Mix starch raw material, solid alkali and calcium carbonate to obtain a mixture, add anhydrous ethanol and premix at low temperature; then evacuate and purge with nitrogen to obtain activated starch; S2. Modification treatment: Add modifier and mix well, then carry out microwave radiation-assisted reaction; The microwave radiation-assisted reaction process is as follows: First, carry out a first-stage microwave radiation with a power density of 7-8 kW / kg, then reduce the power density to 5-6 kW / kg for a second-stage microwave radiation, and finally reduce the power density to 3-4 kW / kg for a third-stage microwave radiation. S3. Post-processing: After the reaction is complete, vacuum the air and cool it to 25°C to obtain the final product. The modifier is an etherifying agent, an esterifying agent, or a cationic reagent; During the microwave radiation-assisted reaction, the temperature reached 30-45℃ in the first stage, 50-60℃ in the second stage, and 70-85℃ in the third stage; the frequency remained at 2450MHz±50MHz in all three stages of microwave radiation. In the microwave-assisted reaction process, after the first and second stages of microwave radiation are completed, microwave radiation needs to be paused for heat preservation; among these, After the first phase of microwave radiation is completed, the ratio of the time for pausing microwave radiation to the time for microwave radiation in the first phase is (0.3~0.5):

1. After the second phase of microwave radiation is completed, the ratio of the time for stopping microwave radiation to the time for microwave radiation in the second phase is (1~2):

1.

2. The method according to claim 1, characterized in that, The starch raw material is selected from any one or a combination of corn starch, tapioca starch, and potato starch; the moisture content of the starch raw material is 10-15%.

3. The method according to claim 1, characterized in that, The solid alkali is sodium hydroxide and / or potassium hydroxide; the amount of the solid alkali used is 1 to 10% of the dry weight of the starch raw material.

4. The method according to claim 1, characterized in that, The amount of calcium carbonate used is 5-15% of the dry weight of the starch raw material.

5. The method according to claim 1, characterized in that, The amount of the modifier used is 5-30% of the dry weight of the starch.

6. The method according to claim 1, characterized in that, The amount of anhydrous ethanol used is 10-20% of the dry weight of the starch raw material.

7. The method according to any one of claims 1-6, characterized in that, The modified starch has a degree of substitution coefficient of variation ≤6.5% and a solubility in cold water ≥90%.

8. The application of the modified starch prepared by the method according to any one of claims 1-7, characterized in that, The applications include using modified starch in food, paper, textile materials, or pharmaceutical materials.

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