Preparation method of high-purity resistant dextrin

Abstract

The invention discloses a preparation method of high-purity resistant dextrin, and relates to the technical field of dietary fibers. Preparing a composite catalyst; pressurizing, homogenizing, heating and gelatinizing the starch slurry to obtain gelatinized starch liquid, adding high-temperature-resistant alpha-amylase into the gelatinized starch liquid to perform high-temperature reaction, adding a composite catalyst to perform high-temperature reaction, adding transglucosidase to perform cooling reaction, and performing centrifugation, activated carbon adsorption decoloration, ceramic membrane ultrafiltration system and ion exchange resin purification to obtain the high-temperature-resistant starch. And carrying out vacuum spray drying on the dextrin slurry to obtain the high-purity resistant dextrin. By introducing the composite catalyst with a multi-aspect regulation function, the limitation of direct combination of multiple enzymes is overcome, and the resistant dextrin prepared by the method has high purity and a highly branched structure, is rich in dietary fiber content, excellent in water solubility, uniform in molecular weight distribution, high in short-chain fatty acid yield and stable in digestion resistance; the method can be compatible with a high-protein / high-fat system, and a high-quality raw material basis is provided for functional low-GI food development.

Description

Technical Field

[0001] The invention relates to the technical field of dietary fiber, in particular to a method for preparing high-purity resistant dextrin. Background Art

[0002] Resistant dextrin, a functional dietary fiber, has attracted significant attention in health food, pharmaceutical carriers, and other fields due to its low calorie content, prebiotic properties, and regulatory effects on glucose and lipid metabolism. Traditional preparation methods often utilize strong acids (such as hydrochloric acid and sulfuric acid) to catalyze starch hydrolysis, followed by high-temperature caramelization or enzymatic modification to obtain the resistant components. However, this method has significant drawbacks: strong acid hydrolysis can easily lead to excessive degradation, producing large amounts of monosaccharides and byproducts such as 5-hydroxymethylfurfural, which reduces product purity; the acidification of the reaction system is difficult to precisely control, which can easily trigger the Maillard reaction, resulting in a dark product color and requiring additional decolorization; and the need for post-acid hydrolysis neutralization produces large amounts of saline wastewater, increasing environmental pressure. In recent years, enzymatic processes have garnered attention due to their mild conditions and high specificity. However, existing technologies lack the synergistic efficiency of enzymatic and acidic hydrolysis, making it difficult to balance the rates of α-1,4 bond cleavage and α-1,6 bond recombination, resulting in a low degree of product branching. Furthermore, enzyme activity is susceptible to pH fluctuations in the reaction system. Furthermore, conventional composite catalysts lack the selective adsorption capacity for reaction intermediates, making them ineffective in suppressing side reactions. This results in a broad molecular weight distribution of the final product, making purification difficult. Therefore, developing an efficient catalytic system that can regulate the reaction process, target impurities, and protect enzyme activity, while simultaneously achieving the green preparation of high-purity resistant dextrin, has become a pressing technical challenge in this field. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing high-purity resistant dextrin to solve the problems raised in the background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for preparing high-purity resistant dextrin comprises the following steps:

[0006] S1. Homogenize a starch slurry with a concentration of 8-12% at 150-200 MPa for 3 times and heat at 85-95°C for 30-40 min to obtain a gelatinized starch solution;

[0007] Furthermore, in step S1, the starch is selected from tapioca starch, corn starch, potato starch or waxy corn starch;

[0008] S2. Add thermostable α-amylase to the gelatinized starch solution, adjust the pH to 5.5-6.0 with citric acid solution, and react at 90-95° C. for 20-30 minutes to obtain enzymatic starch slurry 1;

[0009] Furthermore, in step S2, the dosage of the thermostable α-amylase is 8-12 U per gram of gelatinized starch solution;

[0010] S3, adding 5-7% of the composite catalyst by mass of the gelatinized starch solution to the enzymatically hydrolyzed starch slurry 1, adjusting the pH to 4.5-5.0 with citric acid solution, and reacting at 90-100° C. for 20-30 min to obtain enzymatically hydrolyzed starch slurry 2;

[0011] S4, adding glucosidase to the enzymatically hydrolyzed starch slurry 2, adjusting the pH to 5.0-5.5, reacting at 55-60° C. for 2.5-3 h, centrifuging, and collecting the supernatant to obtain the enzymatically hydrolyzed starch slurry 3;

[0012] Furthermore, in step S4, the amount of the glucose transaminase used is 600-800 U per gram of gelatinized starch solution;

[0013] S5. Add 1-1.2% activated carbon by weight of the enzymatically hydrolyzed starch slurry 3 to the enzymatically hydrolyzed starch slurry 3, perform adsorption decolorization at 50-60° C. for 15-20 min, centrifuge, pass through a ceramic membrane ultrafiltration system, cycle three times, collect the retentate, and pass through a D301 ion exchange resin to obtain a dextrin slurry;

[0014] Furthermore, in step S5, the ceramic membrane ultrafiltration system has a molecular weight cutoff of 2 kDa, a membrane material of zirconia, an operating pressure of 0.2-0.4 MPa, and a temperature of 50-60° C.;

[0015] S6. vacuum spray drying the dextrin slurry to obtain high-purity resistant dextrin;

[0016] Furthermore, in step S6, the vacuum spray drying conditions are: inlet air temperature 170-175°C, vacuum degree -0.08 MPa, and outlet air temperature 80-90°C.

[0017] Furthermore, the steps for preparing the composite catalyst are as follows:

[0018] A1. Mix zirconium phosphate and stearic acid, add lecithin, stir at 150° C. for 2 h, cool to room temperature, grind, wash, and dry to obtain modified zirconium phosphate;

[0019] The mass ratio of the zirconium phosphate, stearic acid and lecithin is 1000:100:3.3.

[0020] A2. Disperse the modified zirconium phosphate in a 4-6% by mass ethanol solution, add zinc nitrate and 2-methylimidazole, stir at room temperature for 24 hours, centrifuge, wash, and dry at 80°C for 6 hours to obtain modified zirconium phosphate@ZIF-8 nanocrystals;

[0021] The usage ratio of the modified zirconium phosphate, ethanol solution, zinc nitrate and 2-methylimidazole is 1 g:20 mL:0.5 g:(1.1-1.6) g;

[0022] A3. The modified zirconium phosphate@ZIF-8 nanocrystals were immersed in a taurine aqueous solution with a pH of 3 and a mass fraction of 5%, reacted at 80°C for 6 hours, centrifuged, washed with deionized water, and dried at 60°C to obtain a composite catalyst.

[0023] The usage ratio of the modified zirconium phosphate @ ZIF-8 nanocrystals and the taurine aqueous solution is 1 g: (28-32) mL.

[0024] It should be noted that zirconium phosphate, as a layered inorganic carrier, has a stearic acid intercalation structure that provides rigid support for the epitaxial growth of ZIF-8. The intercalation of the hydrophobic carbon chain of stearic acid increases the interlayer spacing of the zirconium phosphate layered structure on the one hand, and forms a hydrophobic structure on the other hand. Zinc nitrate and 2-methylimidazole grow epitaxially on the surface of zirconium phosphate in an ethanol solution to form the equally hydrophobic ZIF-8. At the same time, the microenvironment formed by the hydrophobic carbon chain can directionally adsorb hydrophobic impurities (such as lipids). Taurine electrostatically bonds with the phosphate group on the surface of zirconium phosphate through amino protonation, and its sulfonic acid group forms a hydrogen bond with the hydroxyl group at the edge of the zirconium phosphate layer, further stabilizing the loaded structure. The phosphate group of zirconium phosphate is partially deprotonated at pH = 5.5-6.0, releasing H + Catalyzes the cleavage of α-1,4 bonds to generate short-chain dextrins; protonates at pH = 4.5-5.5, inhibiting H + Excessive release inhibits the effects of excessive acidification on glucosidase activity, protecting glucosidase activity and regulating the reaction balance between the S3 acidolysis stage and the S4 transamination stage. Stearic acid intercalation expands the interlayer spacing of zirconium phosphate, allowing small-molecule dextrins to enter the interlayers and contact acidic sites for targeted catalysis. Under acidic conditions, the ZIF-8 surface carries a positive charge, which electrostatically adsorbs negatively charged byproducts (such as 5-hydroxymethylfurfural). This adsorption of impurities simultaneously reduces the Maillard reaction, improves product color, and inhibits side reactions. Taurine electrostatically binds to glucosidase, enhancing the enzyme's thermal stability and reducing thermal denaturation. It also acts as a global antioxidant, scavenging free radicals, inhibiting the oxidative inactivation of glucosidase and protecting enzyme activity.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention overcomes the limitations of directly combining multiple enzymes by introducing a composite catalyst with multi-faceted regulatory functions. In the absence of a composite catalyst, pH fluctuations in an acidic environment can easily lead to enzyme inactivation, a large number of side reaction products that are difficult to separate, difficulty in coordinating the cleavage of α-1,4 bonds and the recombination of α-1,6 bonds, a low degree of product branching, and uneven molecular weight distribution. Adding a composite catalyst between multiple enzymes can directional catalyze the generation of short-chain dextrins, stabilize the activity of transaminase (glucose transaminase), adsorb interfering impurities, ensure efficient and directional reaction, significantly reduce the generation of by-products, and control the molecular weight and degree of branching of the product. At the same time, by combining purification technologies such as activated carbon, ultrafiltration, and resin combination, the purity and color of the product are greatly improved. The resistant dextrin obtained by the present invention has both high purity and a highly branched structure, a uniform molecular weight distribution, stable digestibility, and excellent water solubility. It provides a high-quality raw material basis for the development of functional foods and is suitable for the development of high-value-added foods and pharmaceutical products. At the same time, the process is green and efficient, and has the potential for large-scale production. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0028] Thermostable α-amylase was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (A109182).

[0029] Glucoside transaminase was purchased from Amano Enzyme Preparation (Jiangsu) Co., Ltd. (Shanghai Branch) as EC 3.2.1.20.

[0030] The steps for preparing the composite catalyst are as follows:

[0031] A1. Mix 10 g of zirconium phosphate and 1 g of stearic acid, add 33 mg of lecithin, stir at 150° C. for 2 h, cool to room temperature, grind, wash, and dry to obtain modified zirconium phosphate;

[0032] A2. Disperse 10 g of modified zirconium phosphate in 200 mL of 5% ethanol solution, add 5 g of zinc nitrate and 14 g of 2-methylimidazole, stir at room temperature for 24 h, centrifuge, wash, and dry at 80°C for 6 h to obtain modified zirconium phosphate@ZIF-8 nanocrystals;

[0033] A3. Immerse 10 g of modified zirconium phosphate@ZIF-8 nanocrystals in 300 mL of a 5% taurine aqueous solution with a pH of 3, react at 80°C for 6 h, centrifuge, wash with deionized water, and dry at 60°C to obtain a composite catalyst.

[0034] Example 1

[0035] A method for preparing high-purity resistant dextrin comprises the following steps:

[0036] S1. Homogenize 10% cassava slurry at 180 MPa three times and heat at 90°C for 35 min to obtain gelatinized starch solution;

[0037] S2. Add 10,000 U of thermostable α-amylase to 1 kg of gelatinized starch solution, adjust the pH to 5.8 with citric acid solution, and react at 92°C for 25 minutes to obtain enzymatic starch slurry 1.

[0038] S3, adding 60 g of composite catalyst to 1 kg of enzymatic starch slurry 1, adjusting the pH to 4.8 with citric acid solution, and reacting at 95° C. for 25 min to obtain enzymatic starch slurry 2;

[0039] S4. Add 700,000 U of glucose transaminase to 1 kg of enzymatically hydrolyzed starch slurry 2, adjust the pH to 5.3, react at 58° C. for 2.8 h, centrifuge, and collect the supernatant to obtain enzymatically hydrolyzed starch slurry 3;

[0040] S5, add 11g activated carbon to the enzymatic starch slurry 3, adsorb and decolorize at 55℃ for 18min, centrifuge, collect the supernatant, and pass it through a ceramic membrane ultrafiltration system with a molecular weight cutoff of 2kDa, a membrane material of zirconium oxide, an operating pressure of 0.3MPa, and a temperature of 55℃, cycle 3 times, collect the retentate, and pass it through D301 ion exchange resin to obtain a dextrin slurry;

[0041] S6. Vacuum spray drying the dextrin slurry at an air inlet temperature of 173° C., a vacuum degree of -0.08 MPa, and an air outlet temperature of 85° C. to obtain high-purity resistant dextrin;

[0042] Example 2

[0043] A method for preparing high-purity resistant dextrin comprises the following steps:

[0044] S1. Homogenize 12% cassava slurry at 180 MPa three times and heat at 90°C for 40 min to obtain gelatinized starch solution;

[0045] S2. Add 12,000 U of thermostable α-amylase to 1 kg of gelatinized starch solution, adjust the pH to 5.5 with citric acid solution, and react at 95°C for 30 minutes to obtain enzymatic starch slurry 1.

[0046] S3, adding 60g of composite catalyst to 1kg of enzymatic starch slurry 1, adjusting the pH to 4.5 with citric acid solution, and reacting at 100°C for 30min to obtain enzymatic starch slurry 2;

[0047] S4. Add 800,000 U of glucose transaminase to 1 kg of enzymatically hydrolyzed starch slurry 2, adjust the pH to 5.0, react at 60° C. for 3 h, centrifuge, and collect the supernatant to obtain enzymatically hydrolyzed starch slurry 3;

[0048] S5, add 12g activated carbon to the enzymatic starch slurry 3, adsorb and decolorize at 50-60℃ for 20min, centrifuge, collect the supernatant, and pass it through a ceramic membrane ultrafiltration system with a molecular weight cutoff of 2kDa, a membrane material of zirconium oxide, an operating pressure of 0.4MPa, and a temperature of 60℃, cycle 3 times, collect the retentate, and pass it through D301 ion exchange resin to obtain a dextrin slurry;

[0049] S6. Vacuum spray drying the dextrin slurry at an air inlet temperature of 175° C., a vacuum degree of -0.08 MPa, and an air outlet temperature of 90° C. to obtain high-purity resistant dextrin;

[0050] Example 3

[0051] A method for preparing high-purity resistant dextrin comprises the following steps:

[0052] S1. Homogenize 8% cassava slurry at 180 MPa three times and heat at 90°C for 30 min to obtain gelatinized starch solution;

[0053] S2. Add 8000U of thermostable α-amylase to 1kg of gelatinized starch solution, adjust the pH to 6.0 with citric acid solution, and react at 90°C for 20min to obtain enzymatic starch slurry 1;

[0054] S3, adding 60g of composite catalyst to 1kg of enzymatic starch slurry 1, adjusting the pH to 5.0 with citric acid solution, and reacting at 90°C for 20min to obtain enzymatic starch slurry 2;

[0055] S4. Add 600,000 U of glucose transaminase to 1 kg of enzymatically hydrolyzed starch slurry 2, adjust the pH to 5.5, react at 55° C. for 2.5 h, centrifuge, and collect the supernatant to obtain enzymatically hydrolyzed starch slurry 3;

[0056] S5, add 10g activated carbon to the enzymatic starch slurry 3, adsorb and decolorize at 50℃ for 15min, centrifuge, collect the supernatant, and pass it through a ceramic membrane ultrafiltration system with a molecular weight cutoff of 2kDa, a membrane material of zirconium oxide, an operating pressure of 0.2MPa, and a temperature of 50℃, cycle 3 times, collect the retentate, and pass it through D301 ion exchange resin to obtain a dextrin slurry;

[0057] S6. Vacuum spray drying the dextrin slurry at an air inlet temperature of 170° C., a vacuum degree of -0.08 MPa, and an air outlet temperature of 80° C. to obtain high-purity resistant dextrin;

[0058] Example 4

[0059] A method for preparing high-purity resistant dextrin comprises the following steps:

[0060] S1. Homogenize 11% cassava slurry at 180 MPa three times and heat at 90°C for 38 min to obtain gelatinized starch solution;

[0061] S2. Add 11500U of thermostable α-amylase to 1kg of gelatinized starch solution, adjust the pH to 5.6 with citric acid solution, and react at 94°C for 28min to obtain enzymatic starch slurry 1.

[0062] S3, adding 55g of composite catalyst to 1kg of enzymatic starch slurry 1, adjusting the pH to 4.6 with citric acid solution, and reacting at 99°C for 28min to obtain enzymatic starch slurry 2;

[0063] S4. Add 750,000 U of glucose transaminase to 1 kg of enzymatically hydrolyzed starch slurry 2, adjust the pH to 5.4, react at 59° C. for 2.9 h, centrifuge, and collect the supernatant to obtain enzymatically hydrolyzed starch slurry 3;

[0064] S5, add 11.5g of activated carbon to the enzymatic starch slurry 3, adsorb and decolorize at 58℃ for 19min, centrifuge, collect the supernatant, and pass it through a ceramic membrane ultrafiltration system with a molecular weight cutoff of 2kDa, a membrane material of zirconium oxide, an operating pressure of 0.35MPa, and a temperature of 58℃, cycle 3 times, collect the retentate, and pass it through D301 ion exchange resin to obtain a dextrin slurry;

[0065] S6. Vacuum spray drying the dextrin slurry at an air inlet temperature of 174° C., a vacuum degree of -0.08 MPa, and an air outlet temperature of 78° C. to obtain high-purity resistant dextrin;

[0066] Example 5

[0067] A method for preparing high-purity resistant dextrin comprises the following steps:

[0068] S1. Homogenize 9% cassava slurry at 180 MPa three times and heat at 90°C for 32 min to obtain gelatinized starch solution;

[0069] S2. Add 9000U of thermostable α-amylase to 1kg of gelatinized starch solution, adjust the pH to 5.9 with citric acid solution, and react at 91°C for 29 minutes to obtain enzymatic starch slurry 1;

[0070] S3, adding 60 g of composite catalyst to 1 kg of enzymatic starch slurry 1, adjusting the pH to 4.9 with citric acid solution, and reacting at 93° C. for 23 min to obtain enzymatic starch slurry 2;

[0071] S4. Add 650,000 U of glucose transaminase to 1 kg of enzymatically hydrolyzed starch slurry 2, adjust the pH to 5.4, react at 59° C. for 2.9 h, centrifuge, and collect the supernatant to obtain enzymatically hydrolyzed starch slurry 3;

[0072] S5, add 10.5g activated carbon to the enzymatic starch slurry 3, adsorb and decolorize at 53℃ for 16min, centrifuge, collect the supernatant, pass through a ceramic membrane ultrafiltration system with a molecular weight cutoff of 2kDa, a membrane material of zirconium oxide, an operating pressure of 0.25MPa, a temperature of 53℃, cycle 3 times, collect the retentate, and pass through D301 ion exchange resin to obtain a dextrin slurry;

[0073] S6. Vacuum spray drying the dextrin slurry at an air inlet temperature of 171° C., a vacuum degree of -0.08 MPa, and an air outlet temperature of 82° C. to obtain high-purity resistant dextrin;

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that no composite catalyst is added and S3 is omitted.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that no composite catalyst is added, and unmodified zirconium phosphate is used as the catalyst.

[0078] test:

[0079] (1) Yield: sample dry mass / original starch dry mass × 100%;

[0080] (2) Fiber content: GB / T 5009.88-2023 Determination of dietary fiber in foods;

[0081] (3) Water solubility at 25°C: GB / T 12143-2008 General analytical methods for beverages;

[0082] (4) Reducing sugar content: GB 5009.7-2016 Determination of reducing sugars in foods;

[0083] (5) Ash content: GB 5009.4-2016 Determination of ash content in foods;

[0084] (6) In vitro digestibility: 1 g of sample was dispersed in 100 mL of 0.15 mol / L NaCl simulated gastric fluid preheated to 37°C and containing 1% pepsin at pH 2, and the mixture was shaken for 1 h. The pH was adjusted to 6.8. The mixture was then added to 100 mL of 0.5 mol / L phosphate buffered simulated intestinal fluid (KH2PO4 / NaOH) at pH 6.8 containing 1% pancreatin and shaken for 4 h. 20 mL of 0.5 mol / L NaHCO3 solution was added and mixed rapidly to terminate enzyme activity. 100 mL of 80% ethanol solution was added and vortexed to mix thoroughly, and the mixture was allowed to stand to precipitate undigested residues. The residue was centrifuged, washed, and dried. The in vitro digestibility was calculated using the following formula:

[0085] In vitro digestibility = (initial dry weight - residue dry weight) / initial dry weight × 100%;

[0086] (7) Glycemic index: 1 g of sample was dispersed in 200 mL of 0.15 mol / L NaCl simulated gastric fluid preheated to 37°C and containing 1% pepsin at pH 2, and shaken for 1 h. The pH was adjusted to 6.8, and then added to 200 mL of 0.5 mol / L phosphate buffered simulated intestinal fluid (KH2PO4 / NaOH) containing 1% pancreatin at pH 6.8 and shaken for 4 h. 5 mL of digestive fluid sample was taken, 45 mL of 80% ethanol solution was added, vortexed and mixed, and then centrifuged. 1 mL of supernatant was taken, and 30 mL of GOPOD reagent containing glucose oxidase or peroxidase was added. The mixture was reacted at 37°C for 20 min. The blank control group (distilled water without sample + simulated liquid reagent) was used as a reference. The absorbance at 510 nm was measured to calculate the glucose concentration and the amount of glucose released. The hydrolysis rate and glycemic index were calculated as follows:

[0087] Sample hydrolysis rate (HR 样品 ) = sample glucose release / sample mass × 100%;

[0088] GI 葡萄糖 =100,HR 葡萄糖 =1;

[0089] Glycemic Index (GI) = HR 样品 / HR 葡萄糖 ×100;

[0090] (8) Moisture content: GB 5009.3-2016 Determination of moisture in foods;

[0091] (9) Compatibility of high protein / high fat system (turbidity 1 / turbidity 2): The sample was mixed with 10% whey protein or soybean oil, allowed to stand at 25 °C for 1 h, and the turbidity of the mixture was measured using a turbidimeter;

[0092] (10) Thermal stability (color value): "ISO / CIE 11664-4:2019 Colorimetry Part 4: CIE 1976 Lab color space".

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] As can be seen from Table 1, the resistant dextrins prepared in Examples 1-5 of the present invention have high purity, rich dietary fiber content, excellent water solubility, excellent digestion resistance, excellent thermal stability, low content of impurities such as reducing sugar, moisture and ash, and are compatible with high-protein / high-fat systems, making them excellent low-GI food raw materials.

[0098] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0099] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity resistant dextrin, characterized in that: The following steps are involved: S1. Homogenize a starch slurry with a concentration of 8-12% at 150-200 MPa for 3 times and heat at 85-95°C for 30-40 min to obtain a gelatinized starch solution; S2. Add thermostable α-amylase to the gelatinized starch solution, adjust the pH to 5.5-6.0 with citric acid solution, and react at 90-95° C. for 20-30 minutes to obtain enzymatic starch slurry 1; S3, adding 5-7% of the composite catalyst by mass of the gelatinized starch solution to the enzymatically hydrolyzed starch slurry 1, adjusting the pH to 4.5-5.0 with citric acid solution, and reacting at 90-100° C. for 20-30 min to obtain enzymatically hydrolyzed starch slurry 2; S4, adding glucosidase to the enzymatically hydrolyzed starch slurry 2, adjusting the pH to 5.0-5.5, reacting at 55-60° C. for 2.5-3 h, centrifuging, and collecting the supernatant to obtain the enzymatically hydrolyzed starch slurry 3; S5. Add 1-1.2% activated carbon by weight of the enzymatically hydrolyzed starch slurry 3 to the enzymatically hydrolyzed starch slurry 3, perform adsorption decolorization at 50-60° C. for 15-20 min, centrifuge, collect the supernatant, pass through a ceramic membrane ultrafiltration system, cycle three times, collect the retentate, and pass through a D301 ion exchange resin to obtain a dextrin slurry; S6. Vacuum spray drying the dextrin slurry to obtain high-purity resistant dextrin.

2. The method for preparing a high-purity resistant dextrin according to claim 1, wherein: In step S1, the starch is selected from tapioca starch, corn starch, potato starch or waxy corn starch.

3. The method for preparing a high-purity resistant dextrin according to claim 1, wherein: In step S2, the dosage of the thermostable α-amylase is 8-12 U per gram of gelatinized starch solution.

4. The method for preparing a high-purity resistant dextrin according to claim 1, wherein: The composite catalyst preparation steps are as follows: A1. Mix zirconium phosphate and stearic acid, add lecithin, stir at 150° C. for 2 h, cool to room temperature, grind, wash, and dry to obtain modified zirconium phosphate; A2. Disperse the modified zirconium phosphate in a 4-6% by mass ethanol solution, add zinc nitrate and 2-methylimidazole, stir at room temperature for 24 hours, centrifuge, wash, and dry at 80°C for 6 hours to obtain modified zirconium phosphate@ZIF-8 nanocrystals; A3. The modified zirconium phosphate@ZIF-8 nanocrystals were immersed in a taurine aqueous solution with a pH of 3 and a mass fraction of 5%, reacted at 80°C for 6 hours, centrifuged, washed with deionized water, and dried at 60°C to obtain a composite catalyst.

5. The method for preparing high-purity resistant dextrin according to claim 4, wherein: In the step A1, the mass ratio of the zirconium phosphate, stearic acid and lecithin is 1000:100:3.

3.

6. The method for preparing high-purity resistant dextrin according to claim 4, wherein: In step A2, the usage ratio of the modified zirconium phosphate, ethanol solution, zinc nitrate and 2-methylimidazole is 1 g:20 mL:0.5 g:(1.1-1.6) g.

7. The method for preparing high-purity resistant dextrin according to claim 4, wherein: In step A3, the usage ratio of the modified zirconium phosphate@ZIF-8 nanocrystals and the taurine aqueous solution is 1 g:(28-32) mL.

8. The method for preparing high-purity resistant dextrin according to claim 1, wherein: In step S4, the dosage of the glucoside transaminase is 600-800 U per gram of gelatinized starch solution.

9. The method for preparing high-purity resistant dextrin according to claim 1, wherein: In step S5, the ceramic membrane ultrafiltration system has a molecular weight cut-off of 2 kDa, a membrane material of zirconia, an operating pressure of 0.2-0.4 MPa, and a temperature of 50-60°C.

10. The method for preparing high-purity resistant dextrin according to claim 1, characterized in that: In step S6, the vacuum spray drying conditions are: air inlet temperature 170-175°C, vacuum degree -0.08 MPa, and air outlet temperature 80-90°C.

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