Method for efficiently preparing aminated starch

Abstract

The invention discloses a method for efficiently preparing aminated starch, which is characterized in that starch channel protein is removed, the size of an internal channel is increased and the specific surface area of particles is increased under the condition that a natural particle structure of starch is reserved by combining a pulsed electric field technology with freeze-thaw cycle, assisted by surface micro-gelatinization treatment and combined use of multiple pretreatment methods. The method has the advantages that the high-grafting-rate aminated starch is obtained, the substitution degree is high, complete gelatinization of the starch is not needed, and the defect that a traditional preparation technology depends on complete gelatinization of the starch or expensive enzyme reagents are added to open a particle structure to achieve modification is overcome. The obtained aminated starch is complete in particle structure and high in grafting degree, belongs to hydrophobic modified starch, has a porous particle structure and a high specific surface area, and is suitable for the fields of food packaging films, drug sustained-release carriers and the like. In addition, the positive electricity characteristic of the modified amino starch under the acidic condition and electrostatic attraction of bentonite are utilized, and effective adsorption of heavy metal can be achieved.

Description

Technical Field

[0001] This invention relates to the field of modified starch development technology, and specifically to a method for efficiently preparing aminated starch. Background Technology

[0002] Starch is an essential biopolymer that is abundant in nature. It is not only a source of dietary carbohydrates but also a ubiquitous raw material commonly used in non-food industries. Compared with other polymers, starch is a multifunctional biomaterial with great potential due to its large quantity, low cost, and non-toxicity. However, some characteristics of natural starch granules, such as poor solubility, retrogradation, synergistic effects, thermal decomposition, and high viscosity after gelatinization, limit its industrial applications. Therefore, the field of starch modification has attracted widespread attention from researchers, and a large number of starch modification technologies have been developed, which have an important impact on the economy and society of human life. Existing common starch modification methods include: (1) physical modification (micronization, non-thermal plasma, high pressure, ultrasound, pulsed electric field, γ-irradiation, etc.); (2) chemical modification (etherification, esterification, oxidation, cross-linking, acid hydrolysis, etc.); (3) enzymatic modification (starch debranching enzymes, glycosyltransferases, glycosidases, α-amylase, β-amylase, etc.).

[0003] Chemical modification uses toxic and harmful chemical reagents, which has a certain impact on the environment. It requires strict control of reaction conditions and may leave residues. While enzymatic modification is highly efficient and specific, its high cost hinders industrial application. Pulsed electric fields, by applying high-intensity (1-80 kV / cm), short-pulse (microsecond to millisecond) electric fields, induce electroporation or structural changes in biological cells or macromolecules (such as starch). As a physical modification method, it can precisely modify starch, reduce processing time, and offer the flexibility to adjust parameters to suit different starch sources.

[0004] Aminated starch is a cationic starch incorporating quaternary ammonium groups through an etherification reaction. Its permanently positive charge makes it an indispensable functional bio-based material in industries such as papermaking, textiles, water treatment, and personal care. Traditional starch amination modification techniques rely on completely disrupting the starch granule structure through gelatinization or the addition of enzymes and chemical reagents, thereby opening the starch chains for effective modification. Although these methods have fast reaction rates and uniform distribution of substituent groups, the disruption of the ordered arrangement of starch granules leads to poor product stability and limited applications. Furthermore, the aminosilane coupling agent KH791, a common amination modifier, is prone to self-aggregation in aqueous solution, cross-linking macromolecules through Si-O-Si bonds, ultimately hindering its penetration into the starch interior for modification. Therefore, we propose pretreatment of starch and aminosilane solutions to inhibit the self-aggregation of the aminosilane coupling agent KH791, achieving efficient starch amination while preserving the granule structure. The molecular polarization effect of starch-related proteins in a pulsed electric field is used to remove channel proteins, while the electroporation effect of the pulsed electric field expands the internal channels of the starch. The repeated growth and recrystallization of ice crystals in the channels caused by freeze-thaw cycles can further enlarge the pore size. Combined with the microgelatinization effect of calcium chloride on the starch surface, it significantly promotes the entry of aminosilane KH791 into the starch granules, achieving high amination. The resulting amination starch granules have a complete structure, high grafting degree, simple process, low cost, are easy to store and transport, and have high processing flexibility (e.g., they can be gelatinized first and then used as a wet-end additive in papermaking). Summary of the Invention

[0005] The purpose of this invention is to provide a method for efficiently preparing aminated starch, which solves the problem that existing technologies struggle to achieve efficient modification while preserving the ordered arrangement of starch granules.

[0006] This invention is achieved through the following technical solutions:

[0007] A method for efficiently preparing aminated starch, the method comprising the following steps:

[0008] 1) Pulsed electric field pretreatment: Natural corn starch suspension was pretreated with a pulsed electric field, washed with an ethanol-water solution, and then freeze-dried under vacuum to obtain the first modified starch (modified starch to remove channel proteins); the pulsed electric field treatment conditions were: electric field strength 4~20kV / cm, frequency 40~100Hz, pulse width 6~10μs, and time 10~30min; the aminosilane solution was pretreated with a pulsed electric field under the same pulsed electric field conditions to obtain the first modified aminosilane solution;

[0009] 2) The first modified starch obtained in step 1) is mixed with deionized water to obtain a first modified starch suspension. After being subjected to freeze-thaw cycle treatment, it is mixed with calcium chloride, reacted, and then freeze-dried to obtain the second modified starch. The pore size of the second modified starch is further enlarged and the surface is microgelatinized. The freeze-thaw cycle refers to the repeated freezing and thawing treatment of the first modified starch suspension. One cycle in the freeze-thaw cycle includes the following steps: first freezing at -10~-20℃ for 4~6h, and then thawing at 4℃~room temperature for 6~10h, and the number of cycles is 1-3.

[0010] 3) The second modified starch obtained in step 2) and the first modified aminosilane solution obtained in step 1) are refluxed at 50-65℃ under stable pH conditions. After the reaction is completed, the starch is freeze-dried to obtain amino starch.

[0011] Furthermore, the corn starch suspension is pretreated with a pulsed electric field under the drive of a constant-speed peristaltic pump, and the mass ratio of corn starch to deionized water in the corn starch suspension is 1:4 to 1:3.

[0012] Furthermore, the peristaltic pump has a flow rate of 200 mL / min.

[0013] Furthermore, the volume concentration of the ethanol aqueous solution is 80%~95% (v / v).

[0014] Preferably, the first modified starch is washed three times by suction filtration using an ethanol aqueous solution as a washing agent, and then freeze-dried under vacuum.

[0015] Preferably, the aminosilane in the aminosilane solution is a coupling agent KH791, and its mass ratio with anhydrous ethanol and deionized water is 2:20:5.

[0016] Preferably, in step 2), the concentration of the first modified starch suspension is 30-40% (w / w). Calcium chloride is added to the first modified starch suspension after three freeze-thaw cycles, and the amount of calcium chloride added is 0.5-1.5% (w / w, dry starch basis). The reaction time is 10-45 min, and the mixture is freeze-dried under vacuum after the reaction is completed.

[0017] Preferably, in step 3), the mass ratio of the second modified starch to the first modified aminosilane solution is 1:10 to 1:30.

[0018] Furthermore, the pH of the reaction system is maintained at 3.9-4.1 by acetic acid, and the reflux reaction time is 2-5 hours.

[0019] Preferably, after freeze-drying in step 3), Soxhlet extraction is performed with anhydrous ethanol. The Soxhlet extraction endpoint is when 4 to 8 siphoning phenomena occur. Then, after air-drying, aminoated starch is obtained.

[0020] Furthermore, the air drying process is carried out in a hot air drying oven.

[0021] This invention also protects the highly substituted amino starch obtained by the above-described efficient method for preparing amino starch.

[0022] Compared with traditional aminated starch preparation technology, the present invention has the following advantages:

[0023] (1) This invention combines pulsed electric field technology with freeze-thaw cycles and surface microgelatinization treatment. Multiple pretreatment methods are used in combination to remove starch channel proteins while preserving the natural granular structure of starch, increasing the internal channel size and the specific surface area of ​​the granules. This results in aminated starch with a high grafting rate and a high degree of substitution, eliminating the need for complete starch gelatinization. This avoids the shortcomings of traditional preparation techniques that rely on complete starch gelatinization or the addition of expensive enzymes to open the granular structure for modification. The resulting aminated starch granules have a complete structure and a high degree of grafting. They are hydrophobically modified starches with a porous structure and high specific surface area, making them suitable for food packaging films, drug sustained-release carriers, and other fields. Furthermore, by utilizing the positive charge of the modified aminated starch under acidic conditions and its electrostatic attraction with bentonite, effective adsorption of heavy metals can be achieved.

[0024] (2) The present invention pretreats natural corn starch suspension with pulsed electric field, removes channel proteins by utilizing the molecular polarization effect of starch-related proteins in the electric field, and expands the internal channels of starch by utilizing the electroporation effect of pulsed electric field. The operation is simple, efficient and energy-saving, and the starch can be customized (degree of modification) by threshold parameters.

[0025] (3) The present invention pre-treats the aminosilane solution with a pulsed electric field, and uses the polarization effect of the pulsed electric field to suppress the self-condensation of the aminosilane coupling agent KH791 in the aqueous solution, avoids the formation of macromolecular network side reaction products with Si-O-Si bond crosslinking, and promotes the internal modification of the aminosilane coupling agent KH791 through the starch channel.

[0026] (4) The present invention further expands the starch channels through the repeated generation and recrystallization of ice crystals in the freeze-thaw cycle step.

[0027] (5) The present invention utilizes calcium chloride to microgelatinize the starch surface, thereby destroying the surface film of the particles, which facilitates the entry of aminosilane coupling agent KH791 into the starch particles and effectively grafts it into the internal starch chain to achieve high amination.

[0028] (6) The present invention has a simple process, low cost, easy storage and transportation, and high processing flexibility (e.g., it can be gelatinized first and then used as a wet end additive in papermaking). Attached Figure Description

[0029] Figure 1This is a schematic diagram illustrating the principle of the starch amination reaction and the self-condensation reaction of aminosilane in this invention.

[0030] Figure 2 These are scanning electron microscope images of natural starch and the first modified starch obtained in comparative examples 1, 3, and 4.

[0031] Figure 3 The nitrogen (N) content of amino starch was determined by an elemental analyzer.

[0032] Figure 4 The nitrogen content on the surface of amino starch was determined by XPS.

[0033] Figure 5 It shows the crystal structure and RC value of amino starch. Detailed Implementation

[0034] The following is a further description of the invention, but not a limitation thereof.

[0035] The desktop continuous pulse electric field processing system used in this embodiment is from Guangzhou Paihu Technology Co., Ltd.

[0036] Example 1:

[0037] (1) Pulse electric field pretreatment: A benchtop continuous pulse electric field treatment system was used to continuously treat 300g of natural corn starch suspension (corn starch: deionized water mass = 1:4) for 30min under constant speed peristaltic pump drive. The electric field strength was 8kV / cm, the frequency was 100Hz, the pulse width was 10μs, and the flow rate was 200mL / min. Then, 80% (v / v) ethanol aqueous solution was used as detergent and filtered three times through Buchner funnel. After vacuum freeze drying, the first modified starch was obtained.

[0038] Under the same pulsed electric field conditions, 600g of aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was continuously treated for 30min to obtain the first modified aminosilane solution.

[0039] (2) Freeze-thaw cycle: Dissolve 30g of the first modified starch obtained in step (1) in deionized water to obtain a suspension with a concentration of 30% (w / w) and perform freeze-thaw cycle treatment. First, freeze at -20℃ for 4h and then thaw at 4℃ for 6h. Repeat the freeze-thaw cycle treatment 3 times.

[0040] (3) Surface microgelatinization: Add 1.0% (w / w, dry starch basis) calcium chloride to the freeze-thawed starch suspension (30%, w / w) obtained in step (2), stir and react for 30 min, and then freeze dry under vacuum to obtain the second modified starch;

[0041] (4) Aminosilane coupling: 600g of the first modified aminosilane solution was added to 20g of the second modified starch obtained in step (3), and the mixture was refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 with acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol in a Soxhlet extractor until five siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0042] Example 2:

[0043] (1) Pulsed electric field pretreatment: A benchtop continuous pulsed electric field treatment system was used to continuously treat 300g of natural corn starch suspension (corn starch: deionized water mass = 1:3) for 20min under constant speed peristaltic pump drive. The electric field strength was 20kV / cm, the frequency was 70Hz, the pulse width was 8μs, and the flow rate was 200mL / min. Then, 85% (v / v) ethanol aqueous solution was used as detergent and filtered three times through Buchner funnel. After vacuum freeze drying, the first modified starch was obtained.

[0044] Under the same pulsed electric field conditions, 400g of aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was continuously treated for 30min to obtain the first modified aminosilane solution.

[0045] (2) Freeze-thaw cycle: Dissolve 30g of the first modified starch obtained in step (1) in deionized water to obtain a suspension with a concentration of 33% (w / w). Freeze at -20℃ for 4h and then thaw at 4℃ for 6h.

[0046] (3) Surface microgelatinization: 1.5% (w / w, dry starch basis) calcium chloride was added to the freeze-thawed starch suspension (33%, w / w) obtained in step (2), stirred and reacted for 45 min, and then freeze-dried under vacuum to obtain the second modified starch.

[0047] (4) Aminosilane coupling: 400g of the first modified aminosilane solution was added to 20g of the second modified starch obtained in step (3), and the mixture was refluxed at 65°C for 5h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.1 by acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol in a Soxhlet extractor until seven siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0048] Example 3:

[0049] (1) Pulsed electric field pretreatment: A benchtop continuous pulsed electric field treatment system was used to continuously treat 300g of natural corn starch suspension (corn starch: deionized water mass = 1:3) for 10min under constant speed peristaltic pump drive. The electric field strength was 4kV / cm, the frequency was 40Hz, the pulse width was 6μs, and the flow rate was 200mL / min. Then, 90% (v / v) ethanol aqueous solution was used as detergent and filtered three times through Buchner funnel. After vacuum freeze-drying, the first modified starch was obtained.

[0050] Under the same pulsed electric field conditions, 200g of aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was continuously treated for 30min to obtain the first modified aminosilane solution.

[0051] (2) Freeze-thaw cycle: Dissolve 30g of the first modified starch obtained in step (1) in deionized water to obtain a suspension with a concentration of 36% (w / w) and perform freeze-thaw cycle treatment. First freeze at -20℃ for 4h and then thaw at 4℃ for 6h. Repeat the freeze-thaw cycle treatment twice.

[0052] (3) Surface microgelatinization: Add 0.5% (w / w, dry starch basis) calcium chloride to the freeze-thawed starch suspension (36%, w / w) obtained in step (2), stir and react for 15 min, and then freeze dry under vacuum to obtain the second modified starch;

[0053] (4) Aminosilane coupling: 200g of the first modified aminosilane solution was added to 20g of the second modified starch obtained in step (3), and the mixture was refluxed at 50°C for 2h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 3.9 using acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol in a Soxhlet extractor until six siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0054] Comparative Example 1:

[0055] Referring to Example 1, the difference is that the first modified starch did not undergo freeze-thaw cycling, nor was it subsequently subjected to surface microgelatinization, and the aminosilane dispersion did not undergo pulsed electric field pretreatment. The steps are as follows:

[0056] (1) Pulsed electric field pretreatment of starch: A benchtop continuous pulsed electric field treatment system was used to continuously treat 300g of natural corn starch suspension (corn starch: deionized water mass = 1:4) for 30min under constant speed peristaltic pump drive. The electric field strength was 8kV / cm, the frequency was 100Hz, the pulse width was 10μs, and the flow rate was 200mL / min. Then, 80% (v / v) ethanol aqueous solution was used as detergent and filtered three times through Buchner funnel. After vacuum freeze drying, the first modified starch was obtained.

[0057] (2) Aminosilane Coupling: 600g of an aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was added to 20g of the first modified starch obtained in step (1). The mixture was refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 using acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol extractor until five siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0058] Comparative Example 2:

[0059] Referring to Example 1, the difference is that the corn starch was not pretreated with a pulsed electric field, nor was it subsequently subjected to freeze-thaw cycles and surface microgelatinization. The steps are as follows:

[0060] (1) Pulsed electric field pretreatment of aminosilane solution: 600g of aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was continuously treated for 30min using a benchtop continuous pulsed electric field treatment system under constant speed peristaltic pump. The electric field strength was 8kV / cm, the frequency was 100Hz, the pulse width was 10μs, and the flow rate was 200mL / min to obtain the first modified aminosilane solution.

[0061] (2) Aminosilane coupling: 20g of natural corn starch was added to 600g of the first modified aminosilane solution obtained in step (1), and the mixture was refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 with acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol in a Soxhlet extractor until five siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain amino-modified starch.

[0062] Comparative Example 3:

[0063] Referring to Example 1, the difference is that the corn starch was not pretreated with a pulsed electric field and was directly subjected to freeze-thaw cycles without subsequent surface microgelatinization, and the aminosilane dispersion was not pretreated with a pulsed electric field. The steps are as follows:

[0064] (1) Freeze-thaw cycle pretreatment of starch: 30g of natural corn starch was dissolved in deionized water, and the suspension with a concentration of 30% (w / w) was first frozen and then thawed, and the freeze-thaw cycle was repeated 3 times. The freeze-thaw cycle conditions included freezing at -20℃ for 4h and then thawing at 4℃ for 6h as one freeze-thaw cycle, and vacuum freeze-drying to obtain the first modified starch;

[0065] (2) Aminosilane Coupling: 600g of an aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was added to 20g of the first modified starch obtained in step (1). The mixture was refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 using acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol extractor until five siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0066] Comparative Example 4:

[0067] Referring to Example 1, the difference is that the corn starch was not pretreated with a pulsed electric field, nor was it subjected to freeze-thaw cycles, and the aminosilane dispersion was not pretreated with a pulsed electric field. The steps are as follows:

[0068] (1) Surface microgelatinization pretreated starch: 30g of natural corn starch was prepared into a suspension (30%, w / w), 1.0% (w / w, dry starch basis) of calcium chloride was added, the mixture was stirred and reacted for 30min, and then vacuum freeze-dried to obtain the first modified starch;

[0069] (2) Aminosilane Coupling: 600g of an aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was added to 20g of the first modified starch obtained in step (1). The mixture was refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 using acetic acid. After the reaction was completed, the mixture was freeze-dried. Then, Soxhlet extraction was performed in an anhydrous ethanol extractor until five siphoning phenomena occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain the amino-modified starch.

[0070] Comparative Example 5:

[0071] Referring to Example 1, the difference lies in that the corn starch was not pretreated with a pulsed electric field, nor was it subjected to freeze-thaw cycles and surface microgelatinization, and the aminosilane dispersion was not pretreated with a pulsed electric field. The steps are as follows:

[0072] Direct aminosilane coupling: 600g of an aminosilane dispersion (aminosilane coupling agent KH791: anhydrous ethanol: deionized water mass = 2:20:5) was added to 20g of natural corn starch and refluxed at 60℃ for 3h using a flat-bottomed flask and a serpentine condenser. The pH of the reaction system was maintained at 4.0 using acetic acid. After the reaction, the mixture was lyophilized. Then, Soxhlet extraction was performed in an anhydrous ethanol apparatus until five siphoning events occurred. Finally, the mixture was dried overnight in a hot air dryer to obtain amino-modified starch.

[0073] To further illustrate the technical effects of the present invention, measurements were performed on the relevant samples obtained from Examples 1-3 and Comparative Examples 1-5.

[0074] I. Effects of different pretreatment methods on starch microstructure

[0075] Freeze-dried starches after different pretreatments were fixed onto an aluminum substrate using double-sided tape and then plated with a gold-palladium alloy layer. The effects of different pretreatment methods on the microstructure of starch were observed using a scanning electron microscope at 5000x magnification and 2.0kV accelerating voltage.

[0076] II. Determination of nitrogen content in the prepared amino starch

[0077] The content of C, H, O, and N atoms in amino starch was determined using an elemental analyzer.

[0078] III. Surface Chemical Composition of the Prepared Amino Starch

[0079] The Si element content (based on the total number of C, O, N, and Si atoms) at a depth of 5-10 nm on the surface of amino starch was determined using X-ray photoelectron spectroscopy. The experiments were conducted using a monochromatic Al-Kα X-ray source with an accelerating voltage set to 15 kV, below 1.0 × 10⁻⁶ kV. -9 The experiment was conducted under high vacuum conditions in Torr.

[0080] IV. Determination of nitrogen content in the prepared amino starch

[0081] The crystal structure of amino starch was determined using a fixed-target X-ray diffractometer. The diffraction angle 2θ ranged from 10° to 25° under conditions of 40 kV voltage and 40 mA current. The relative crystallinity (RC) was calculated using MDI Jade 6 analysis software, with the formula: RC (%) = Ac / (Ac + Aa) × 100%.

[0082] The reaction mechanism of starch with aminosilane coupling agent KH791 is as follows: Figure 1 As shown, silane undergoes initial hydrolysis to generate 1-silanol, ultimately producing an intermediate containing trisilanol functional groups. This intermediate then dehydrates with hydroxyl groups on the starch chain to yield amino starch. Trisilanol, as a highly reactive group, readily undergoes self-aggregation. This side reaction ultimately generates a large polymer linked by -Si-O-Si- molecules, which is difficult to penetrate into the starch granules for modification. Figure 2 The results show that different individual pretreatment methods have a significant impact on starch structure. Specifically, natural starch has a smooth and dense surface. After pulsed electric field treatment, significant pore channels appear on the surface. Although natural starch already has a small number of channels, the pulsed electric field significantly enlarges the pore size. Starch treated with freeze-thaw cycles shows obvious depressions on the surface of starch granules due to ice crystal growth and recrystallization. The surface structure of starch granules microgelatinized with CaCl2 is significantly disrupted, with pore sizes increasing by tens of times and the crystal structure becoming more loosely structured. Test results indicate that the nitrogen atom content in natural starch is less than 0.01%, negligible. Therefore, nitrogen atoms were introduced by the aminosilane coupling agent KH791. Figure 3 It can be seen that, compared with Comparative Example 5, Comparative Examples 1, 3, and 4 increased the nitrogen atom content, indicating that the grafting degree of corn starch is higher after pulsed electric field pretreatment, freeze-thaw cycle treatment, or surface microgelatinization. It is particularly noteworthy that the degree of substitution in Example 1 increased by 144% compared with Comparative Example 5, indicating that the combined pretreatment of pulsed electric field with freeze-thaw cycle and surface microgelatinization is more effective than any single pretreatment method. Compared with Comparative Example 5, Comparative Example 2 has a higher nitrogen atom content, indicating that the inhibition of self-condensation reaction by the pulsed electric field promotes the entry of the aminosilane modifier KH791 into the particle interior. Figure 4 The identical N atom content on the surface of amino starch in Comparative Examples 2 and 5 further confirms this conclusion: the improved modification efficiency of the aminosilane modifier KH791 through pulsed electric field pretreatment is achieved by promoting internal grafting, rather than altering the surface grafting degree. Furthermore, Figure 4 The surface nitrogen (N) content of natural starch decreased significantly after pulsed electric field pretreatment, indicating that some surface or channel proteins may have been removed. This is consistent with... Figure 1 Consistent with larger apertures. (By...) Figure 5 It can be seen that pretreatment does not change the crystal form but destroys the microcrystalline region. Compared with natural starch, the RC of amino starch is significantly reduced, indicating that the substitution reaction mainly occurs in the microcrystalline region, and the greater the degree of substitution, the lower the RC. Compared with the amino starch in Comparative Example 5, the amino starch in Comparative Example 1 and Comparative Example 2 has a lower RC value, which is due to more aminosilane coupling agent KH791 entering the particle interior to carry out the substitution reaction.

[0083] In summary, pretreatment of starch can significantly improve its amination efficiency. Furthermore, the pulsed electric field utilizes the polarization effect to suppress the self-aggregation of the aminosilane coupling agent KH791 aqueous solution, further enhancing the grafting degree. The efficient method for preparing aminated starch of this invention significantly improves the amination modification effect without completely destroying the natural granular structure of starch. The pretreatment method used is simple and controllable, and has good application value.

[0084] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for efficiently preparing aminated starch, characterized in that, The method includes the following steps: 1) Pulsed electric field pretreatment: Natural corn starch suspension was pretreated with a pulsed electric field, washed with an ethanol-water solution, and then freeze-dried under vacuum to obtain the first modified starch; the pulsed electric field treatment conditions were: electric field strength 4~20kV / cm, frequency 40~100Hz, pulse width 6~10μs, and time 10~30min; the aminosilane solution was pretreated with a pulsed electric field under the same pulsed electric field conditions to obtain the first modified aminosilane solution; 2) The first modified starch obtained in step 1) is mixed with deionized water to obtain a first modified starch suspension. After being subjected to freeze-thaw cycle treatment, it is mixed with calcium chloride, reacted, and then freeze-dried to obtain the second modified starch. The freeze-thaw cycle refers to the repeated freezing and thawing treatment of the first modified starch suspension. One cycle in the freeze-thaw cycle includes the following steps: first freezing at -10~-20℃ for 4~6h, and then thawing at 4℃~room temperature for 6~10h, and the number of cycles is 1-3. 3) The second modified starch obtained in step 2) and the first modified aminosilane solution obtained in step 1) are refluxed at 50-65℃ under stable pH conditions. After the reaction is completed, the starch is freeze-dried to obtain amino starch.

2. The method according to claim 1, characterized in that, The corn starch suspension is pretreated with a pulsed electric field under the drive of a constant-speed peristaltic pump. The mass ratio of corn starch to deionized water in the corn starch suspension is 1:4 to 1:

3.

3. The method according to claim 2, characterized in that, The peristaltic pump has a flow rate of 200 mL / min.

4. The method according to claim 1, characterized in that, The volume concentration of the ethanol aqueous solution is 80%~95%.

5. The method according to claim 1, characterized in that, The first modified starch was washed three times by suction filtration using an ethanol aqueous solution as a washing agent, and then freeze-dried under vacuum.

6. The method according to claim 1, characterized in that, The aminosilane in the aminosilane solution is a coupling agent KH791, and its mass ratio with anhydrous ethanol and deionized water is 2:20:

5.

7. The method according to claim 1, characterized in that, Step 2) The mass concentration of the first modified starch suspension is 30~40%. Calcium chloride is added to the first modified starch suspension after three freeze-thaw cycles. The amount of calcium chloride added is 0.5~1.5 wt.% of the dry starch. The reaction time is 10~45 min. After the reaction is completed, the starch is freeze-dried under vacuum.

8. The method according to claim 1, characterized in that, In step 3), the mass ratio of the second modified starch to the first modified aminosilane solution is 1:10 to 1:

30.

9. The method according to claim 1, characterized in that, In step 3), the pH of the reaction system is maintained at 3.9-4.1 by acetic acid, and the reflux reaction time is 2-5 hours.

10. The method according to claim 1, characterized in that, Step 3) After freeze-drying, Soxhlet extraction is performed with anhydrous ethanol. The Soxhlet extraction endpoint is when 4 to 8 siphon phenomena occur. Then, after air drying, aminoated starch is obtained. The air drying is carried out in a hot air drying oven.

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