Rice starch with high content of resistant starch and preparation method thereof

Abstract

The invention provides rice starch with high content of resistant starch and a preparation method of the rice starch, polylysine-Fe3O4-hyaluronic acid magnetic porous gel is added into rice milk, positive electricity of polylysine and negative electricity of protein adsorb rice protein through electrostatic interaction, high-speed centrifugation and electrostatic interaction are used for cooperating with each other, and the rice starch with high content of resistant starch is obtained. The rice starch with higher purity is extracted; then, the rice starch is subjected to gradient microwave treatment and low-temperature crystallization aging in cooperation, the rice starch with the high content of resistant starch is finally prepared, and the functional value of the rice starch is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of functional starch preparation, and particularly relates to rice starch with a high content of resistant starch and a preparation method thereof. Background Art

[0002] Resistant starch cannot be digested and degraded by enzymes in the gastrointestinal tract and has physiological functions similar to dietary fiber. Research has shown that resistant starch can be fermented and degraded by intestinal microorganisms in the rectum, modulating the structure of the intestinal microbiome, thereby influencing intestinal hormone levels and the physiological functions of the pituitary gland, gonads, and pancreas, thereby exerting blood sugar and lipid-lowering effects. In recent years, the number of people suffering from "three highs" (high blood sugar, high blood sugar, and high cholesterol) in my country has continued to grow. Statistics by the end of 2016 show that the number of people with diabetes in China has reached nearly 200 million. To control the prevalence of diabetes in my country and prevent and treat it, it is necessary to address this issue by using advanced processing technologies in everyday foods to adjust the structure of starch and thus control its digestibility. This is a key direction for the development of starch products and is in line with the requirements of the "Healthy China 2030" Outline. Rice is primarily composed of starch and small amounts of protein, lipids, fiber, minerals, vitamins, and phenolic compounds. Approximately 80% of this is starch, and 8% is protein. Protein can denature at high temperatures or extreme pH conditions, forming complexes with starch, inhibiting the rearrangement or crystallization of starch chains and hindering the formation of resistant starch. Therefore, the production of rice starch with a high resistant starch content requires extracting high-purity rice starch to prevent impurities from interfering with subsequent processing. Currently, the main starch extraction methods include alkali leaching and enzymatic methods. In the alkali leaching method, rice is first soaked in dilute alkali, the alkali solution is removed, and fresh alkali solution is added for wet milling. The rice is then placed in a sedimentation tank for particle size classification, and the upper clear solution is removed. The lower starch emulsion is then centrifuged and dehydrated to separate the starch. However, the starch structure obtained under alkaline conditions is easily damaged, resulting in high protein residues. Starch with excessively high protein content is prone to deterioration, and protein can react with glucose converted from the starch to produce non-enzymatic browning. Furthermore, the alkali leaching method has a long production cycle, high costs, and is prone to environmental pollution. The enzymatic method uses proteases to hydrolyze proteins, making them easier to separate from starch. This method is non-destructive to rice starch, has low production costs, and is pollution-free. However, in the process of extracting rice protein from rice starch using existing composite enzyme methods, due to the small rice starch granules and the large molecular weight of the protein, the large protein fragments after hydrolysis have a similar specific gravity to some starch granules. During cyclonic separation, the starch and protein cannot be effectively separated. In order to reduce the protein content in the starch and obtain higher-purity rice starch, it is necessary to remove as much protein as possible and increase the starch extraction rate. Therefore, it is necessary to prepare a high-purity rice starch with a high content of resistant starch to enhance the functional value of rice starch. Summary of the Invention

[0003] Technical problem to be solved: In response to the above problems, the purpose of the present invention is to provide a rice starch with a high content of resistant starch and a preparation method thereof. Polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added to rice slurry. The positive charge of polylysine and the negative charge of protein adsorb rice protein through electrostatic interaction. High-speed centrifugation is used to cooperate with the electrostatic interaction to extract rice starch with higher purity. The rice starch is then treated with gradient microwaves and combined with low-temperature crystallization and aging to prepare rice starch with a high content of resistant starch.

[0004] Technical solution: A method for preparing rice starch with a high content of resistant starch, comprising the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, and water was added and mixed to obtain a concentration of 10-15wt.% rice milk; S2. rice starch extraction: polylysine-Fe3O4@ hyaluronic acid magnetic porous gel was added to rice slurry, stirred, and centrifuged at a speed of 8000-10000rpm for 5-10min. After removing the supernatant, an external magnetic field was applied to the precipitate to isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel. The remaining precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch is mixed with water, stirred evenly to form a suspension, and then subjected to gradient microwave treatment, low-temperature aging, centrifugation, water washing and precipitation, drying, and pulverization to obtain rice starch with a high content of resistant starch. Furthermore, the preparation method of the polylysine-Fe3O4@hyaluronic acid magnetic porous gel in step S2 is as follows: Step 1: Disperse Fe3O4 powder in 0.1M sodium citrate solution, sonicate and centrifuge to obtain carboxylated Fe3O4; Step 2: Dissolve hyaluronic acid in deionized water, add carboxylated Fe3O4, stir evenly, and freeze-dry to prepare Fe3O4@hyaluronic acid magnetic porous gel; Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1-0.2% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in the polylysine solution, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Furthermore, in step 1, the mass volume ratio of Fe3O4 powder to sodium citrate solution is 1g:(10-20)mL. Furthermore, in step 2, the mass volume ratio of hyaluronic acid, carboxylated Fe3O4 and deionized water is (4-5) mg: (1-3) mg: 1 mL. Furthermore, in step 4, the mass volume ratio of the Fe3O4@hyaluronic acid magnetic porous gel to the polylysine solution is 1 g:(10-50) mL. Furthermore, in step S2, the mass volume ratio of the polylysine-Fe3O4@hyaluronic acid magnetic porous gel to the rice milk is 1 g:(100-200) mL. Furthermore, in step S3, the material-liquid ratio of rice starch to water is 1 g:(3-5) mL. Furthermore, the gradient microwave treatment in step S3 is a three-stage process, wherein the first stage is 700-800W, 95-100°C for 2-5 min; the second stage is 400-600W, 70-80°C for 20-40 min; and the third stage is 200-250W, 50-60°C for 10-20 min. Furthermore, the low-temperature aging conditions in step S3 are 4° C. and low-speed stirring at 100-150 rpm for 24-48 hours. The rice starch with high content of resistant starch prepared by the preparation method. Beneficial effects: 1. The present invention prepares polylysine-Fe3O4@hyaluronic acid magnetic porous gel. The carboxyl groups on the surface of polylysine react with the amino groups on the surface of the hyaluronic acid hydrogel to form a covalent bond. Combined with the positive charge of polylysine and the negative charge of hyaluronic acid, polylysine is ultimately modified on the surface and pore walls of the hyaluronic acid magnetic porous gel. 2. the present invention adds polylysine-Fe in Rice milk o hyaluronic acid magnetic porous gel, unfermented Rice milk is usually close to neutrality (pH is about 6-7), and the pI of protein is 5.6, now pH>pI, protein is negatively charged, and the polylysine on the magnetic porous gel is positively charged under neutral conditions, and can adsorb the rice protein that part cannot be separated from starch by electrostatic interaction; In addition, after adding the magnetic porous gel, Rice milk is carried out to high-speed centrifugation, the strong centrifugal force that high-speed centrifugation produces can accelerate the sedimentation of gel, impel the protein in Rice milk and gel to collide and contact more frequently simultaneously, this dynamic process can promote absorption to a greater extent, therefore by high-speed centrifugation coordinated electrostatic interaction, can realize more efficient, low-cost protein separation, obtain higher-purity rice starch; 3. in the present invention, magnetic porous gel can separate rice protein and polylysine-Fe under the effect of an external magnetic field after protein adsorption, and can also continue to be put into use after removing the protein on the magnetic gel, realizing efficient recovery and reuse; 4. The present invention adopts gradient microwave treatment to cooperate with low-temperature crystallization and aging to prepare rice starch with high content of resistant starch on the extracted rice starch. Conventional microwave treatment usually adopts single power and short-time treatment, but easily lacks the retrogradation stage, so that the resistant starch production is low. The present invention adopts gradient microwave treatment, and the gradient microwave is divided into three sections. The first stage is a high-temperature short-time microwave stage, which quickly destroys the starch granule structure, promotes gelatinization and freeing of amylose; the second stage is a medium-temperature maintenance microwave stage, which promotes the partial breakage and reorganization of starch chains; the third stage is a low-temperature polarized microwave stage, which promotes the ordering of groups (such as hydroxyl groups) and lays the foundation for subsequent crystallization; then the starch suspension after microwave treatment is rapidly cooled to 4°C, stirred at low speed and aged to promote the rearrangement of molecular chains to form a high-crystallinity structure, and the low-temperature treatment promotes the free amylose molecules to re-associate through hydrogen bonds to form a double helix structure (i.e., retrogradation), thereby forming resistant starch. The synergistic effect of the two significantly improves the content of resistant starch, and finally prepares functional rice starch. DETAILED DESCRIPTION The present invention will be further described below in conjunction with examples, which are provided to explain the present invention and are not limited to the following examples: Example 1 The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4. Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to obtain Fe3O4@hyaluronic acid magnetic porous gel. Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution with a mass-to-volume ratio of 1 g:10 mL, shake to mix, wash, and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Example 2 The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4. Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to obtain Fe3O4@hyaluronic acid magnetic porous gel. Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution with a mass volume ratio of 1 g:20 mL, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Example 3 The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4. Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to obtain Fe3O4@hyaluronic acid magnetic porous gel. Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution with a mass volume ratio of 1 g:30 mL, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Example 4 The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4. Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to obtain Fe3O4@hyaluronic acid magnetic porous gel. Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution with a mass volume ratio of 1 g:40 mL, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Example 5 The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4. Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to obtain Fe3O4@hyaluronic acid magnetic porous gel. Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution with a mass volume ratio of 1 g:50 mL, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Comparative Example 1 The difference between this comparative example and Example 5 is that no polylysine modification is added, specifically as follows: The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows: Step 1: Disperse 1g of Fe3O4 powder in 15mL of 0.1M sodium citrate solution, sonicate, and centrifuge to obtain carboxylated Fe3O4; Step 2: Dissolve 80mg of hyaluronic acid in 20mL of deionized water, add 20mg of carboxylated Fe3O4, stir evenly, and freeze-dry to prepare Fe3O4@hyaluronic acid magnetic porous gel. Performance testing: (1) Porosity Table 1 Porosity of polylysine-Fe3O4@hyaluronic acid magnetic porous gels prepared in Examples 1-5 and Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Porosity (%) 78.1 79.5 80.2 78.6 80.3 79.7 (2) Protein adsorption experiment The polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Examples 1-5 and Comparative Example 1 was reacted with 0.1 mg / mL BSA solution in a constant temperature oscillator. After reaching adsorption equilibrium, the supernatant was collected and the absorbance was measured at 280 nm. The residual protein concentration (C e ), the protein adsorption amount can be calculated by the following formula: Q=(C0-C e )×V / m Where, Q is the amount of protein adsorbed (mg / g); C0 is the protein concentration before adsorption (mg / mL); C e is the protein concentration of the supernatant after adsorption (mg / mL); V is the volume of the initial solution (mL); and m is the mass of the magnetic porous gel (g). Table 2 Protein adsorption capacity of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Examples 1-5 and Comparative Example 1 Combined with the porosity in Table 1 and the protein adsorption amount in Table 2, it can be seen that the use of porous structure and polylysine modification of magnetic porous gel can improve the protein adsorption performance. However, in Comparative Example 1, the magnetic porous gel prepared without adding polylysine modification has a significantly decreased protein adsorption amount. Therefore, Example 5 was comprehensively selected for the subsequent preparation of rice starch with a high content of resistant starch. Example 6 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: 1g of polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared in Example 5 was added to 100mL rice milk, stirred, and centrifuged at 10000rpm for 5min. After removing the supernatant, an external magnetic field was applied to precipitate to isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel. The remaining precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 7 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 120mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 8 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 9 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 180mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 10 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: 1g of polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared in Example 5 was added to 200mL rice milk, stirred, and centrifuged at 10000rpm for 5min. After removing the supernatant, an external magnetic field was applied to precipitate to isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel. The remaining precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 11 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 800 W and 100° C. for 4 min; the second stage is 500 W and 75° C. for 30 min; the third stage is 200 W and 50° C. for 15 min, followed by low-speed stirring at 4° C. and 100 rpm for 24 h, centrifugation, washing the precipitate with water, drying, and pulverization to obtain rice starch with a high content of resistant starch. Example 12 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 600 W and 70°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Example 13 A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 250 W and 60°C for 10 min, and the mixture is stirred at a low speed of 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Comparative Example 2 The difference between this comparative example and Example 8 is that no polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added. Specifically, a method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. Rice starch extraction: The rice slurry was centrifuged at 10,000 rpm for 5 min, and the supernatant and precipitate were obtained. The precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Comparative Example 3 The difference between this comparative example and Example 8 is that the polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Comparative Example 1 is as follows: A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. Rice starch extraction: 1g of polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared in Comparative Example 1 was added to 150mL Rice Milk and stirred, and centrifuged at 10000rpm for 5min. After removing the supernatant, an external magnetic field was applied to the precipitate to isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel. The remaining precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Comparative Example 4 The difference between this comparative example and Example 8 is that high-speed centrifugation was not used, as follows: A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. Rice starch extraction: 1g of polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared in Example 5 was added to 150mL rice milk and stirred. An external magnetic field was applied to separate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and the precipitation was separated and dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Comparative Example 5 The difference between this comparative example and Example 8 is that high-speed centrifugation is first performed, and then polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added, specifically as follows: A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: 150mL rice slurry is centrifuged at high speed for 5min at 10000rpm, the supernatant is removed, appropriate water is added to the precipitation and the polylysine-Fe prepared by adding 1g Example 5 O @ hyaluronic acid magnetic porous gel is added, stirred, and an external magnetic field is applied to the precipitation to isolate the complex of rice protein and polylysine-Fe O @ hyaluronic acid magnetic porous gel, and the remaining precipitation is dried to obtain high-purity rice starch; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment. The first stage is 700 W and 95°C for 3 min; the second stage is 500 W and 75°C for 30 min; the third stage is 200 W and 50°C for 15 min, and low-speed stirring is performed at 4°C and 100 rpm for 24 h, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Comparative Example 6 The difference between this comparative example and Example 8 is that gradient microwaves were not used, but only single microwaves were used, as follows: A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water were mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then microwaved at 800 W for 10 min. The suspension was stirred at a low speed of 100 rpm at 4°C for 24 h, centrifuged, washed with water, precipitated, dried, and pulverized to obtain rice starch with a high content of resistant starch. Comparative Example 7 The difference between this comparative example and Example 8 is that low-temperature aging is not used, and the details are as follows: A method for preparing rice starch with a high content of resistant starch comprises the following steps: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, water was added and mixed to give a concentration of 10wt.% rice milk; S2. rice starch extraction: to 150mL rice slurry, add 1g polylysine-Fe3O4@ hyaluronic acid magnetic porous gel prepared by Example 5, stir, 10000rpm high-speed centrifugation 5min, after removing the supernatant, precipitate external magnetic field, isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and obtain high-purity rice starch after the remaining precipitate is dried; S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch and water are mixed at a solid-liquid ratio of 1 g:4 mL, stirred evenly to form a suspension, and then subjected to gradient microwave treatment: the first stage is 700 W, 95 ° C. treatment for 3 min; the second stage is 500 W, 75 ° C. treatment for 30 min; the third stage is 200 W, 50 ° C. treatment for 15 min, centrifuged, washed with water, precipitated, dried, and crushed to obtain rice starch with a high content of resistant starch. Performance testing: (1) Starch purity The rice starch obtained in the preparation process of Examples 6-13 and Comparative Examples 2-7 was subjected to purity determination, and the starch purity determination was performed using the Megazyme kit method. Table 3 Purity of rice starch prepared in Examples 6-13 and Comparative Examples 2-7 Rice starch purity (%) Rice starch purity (%) Example 6 99.14 Example 13 99.23 Example 7 99.21 Comparative Example 2 92.58 Example 8 99.67 Comparative Example 3 93.78 Example 9 99.44 Comparative Example 4 83.06 Example 10 99.07 Comparative Example 5 93.77 Example 11 98.18 Comparative Example 6 99.05 Example 12 99.06 Comparative Example 7 98.86 As shown in Table 3, the rice starch purity extracted by the embodiment is 98.18-99.67%, and comparative example 2 does not add polylysine-Fe3O4@ hyaluronic acid magnetic porous gel, and only by high-speed centrifugation, the rice starch purity decreases; Comparative example 3 adopts the magnetic porous gel prepared by comparative example 1, and unmodified polylysine reduces the rice protein removal ability, and starch purity also decreases; Comparative example 4 does not use high-speed centrifugation, and only by polylysine-Fe3O4@ hyaluronic acid magnetic porous gel adsorption rice protein, electrostatic adsorption effect is limited, so the rice starch purity also decreases; Comparative example 5 first high-speed centrifugation adds gel again, and the promotion effect of high-speed centrifugation on gel adsorption in the embodiment cannot be reached, and the rice starch purity decreases slightly; Comparative example 6 does not carry out gradient microwave, and comparative example 7 does not adopt low-temperature aging, and the purity of rice starch is not significantly affected. Therefore, it can be seen that the present invention adopts high-speed centrifugation in conjunction with electrostatic interaction to achieve more efficient and low-cost protein separation, thereby preparing rice starch with higher purity, laying the foundation for the subsequent preparation of rice starch with a high content of resistant starch. (2) Resistant starch content Method for determining the content of rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS): 1 g of rice starch with high resistant starch content prepared in Examples 6-13 and Comparative Examples 2-7 was placed in a centrifuge tube, 10 mL of distilled water was added and boiled for 15 min, and the mixture was continuously shaken and mixed in a water bath, and then cooled in a 37°C water bath; 10 mL of pH 1.5 HCl-KCl buffer solution was added and mixed, and then 2.8 mL of Mix 0.1g / mL pepsin solution and shake in a 37°C water bath for 1 hour. Adjust the pH to neutral. Add 10mL of 0.2mol / L sodium acetate buffer (pH 5.2) and mix thoroughly. Add 5mL of a mixed enzyme solution of porcine pancreatic α-amylase and amyloglucosidase, shake in a 37°C water bath, and hydrolyze for 0, 20, and 120 minutes. Then, aspirate 0.2mL of the hydrolyzate and inactivate the enzymes in a boiling water bath for 5 minutes. Dilute the hydrolyzate sample with distilled water to an appropriate multiple based on the estimated glucose content. Centrifuge at 8000 rpm for 10 minutes. Take 2mL of the supernatant and colorimetrically determine the glucose content at 510 nm using the DNS method for the determination of reducing sugars. Calculate the slowly digestible starch (SDS), rapidly digestible starch (RDS), and resistant starch (RS) contents as follows: SDS%=(G120-G20)×0.9 / W RDS%=(G20-FG)×0.9 / W RS%=(W-SDS-RDS) / W Where: G20, the amount of glucose produced after 20 min of starch hydrolysis (mg); G120, the amount of glucose produced after 120 min of starch hydrolysis (mg); FG, the free glucose content before enzymatic hydrolysis; W, the total amount of starch (mg). Table 4 Resistant starch content of rice starch prepared in Examples 6-13 and Comparative Examples 2-7 As shown in Table 4, the resistant starch content in the rice starch with high-content resistant starch prepared by the embodiment of the present invention is 26.22-29.86%. Comparative Examples 2-4 are relatively low in purity due to the rice starch prepared in the early stage, which causes certain interference to the processing of subsequent high-resistant starch; Comparative Example 5 is first centrifuged at high speed and then gel is added, and the resistant starch content is reduced compared with the embodiment; Comparative Example 6 does not adopt gradient microwave treatment of rice starch, and conventional microwave treatment usually adopts single power and short-time treatment, but easily lacks the retrogradation stage, so that the resistant starch production amount is low; Comparative Example 7 does not adopt low-temperature aging, and the resistant starch content is significantly reduced compared with the embodiment, and low-speed stirring aging can promote molecular chain rearrangement to form a high crystallinity structure, and low-temperature treatment promotes free amylose molecules to re-associate by hydrogen bonds, forming a double helical structure (i.e. retrogradation), and then forming resistant starch. Therefore, it can be seen that the present invention carries out gradient microwave and low-temperature aging synergistic treatment to rice starch, which is more conducive to the generation of resistant starch. The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing rice starch with a high content of resistant starch, characterized in that: The following steps are involved: S1. Raw material processing: Rice was soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour, and water was added and mixed to obtain a concentration of 10-15wt.% rice milk; S2. rice starch extraction: polylysine-Fe3O4@ hyaluronic acid magnetic porous gel was added to rice slurry, stirred, and centrifuged at a speed of 8000-10000rpm for 5-10min. After removing the supernatant, an external magnetic field was applied to the precipitate to isolate the complex of rice protein and polylysine-Fe3O4@ hyaluronic acid magnetic porous gel. The remaining precipitate was dried to obtain high-purity rice starch. S3. Preparation of rice starch with a high content of resistant starch: High-purity rice starch is mixed with water, stirred evenly to form a suspension, and then subjected to gradient microwave treatment, low-temperature aging, centrifugation, water washing and precipitation, drying, and pulverization to obtain rice starch with a high content of resistant starch.

2. The method for preparing rice starch with a high content of resistant starch according to claim 1, wherein: The preparation method of the polylysine-Fe3O4@hyaluronic acid magnetic porous gel in step S2 is as follows: Step 1: Disperse Fe3O4 powder in 0.1M sodium citrate solution, sonicate and centrifuge to obtain carboxylated Fe3O4; Step 2: Dissolve hyaluronic acid in deionized water, add carboxylated Fe3O4, stir evenly, and freeze-dry to prepare Fe3O4@hyaluronic acid magnetic porous gel; Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1-0.2% polylysine solution; Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in the polylysine solution, shake to mix, wash and dry to obtain the polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

3. The method for preparing rice starch with a high content of resistant starch according to claim 2, wherein The mass volume ratio of Fe3O4 powder to sodium citrate solution in step 1 is 1g:(10-20)mL.

4. The method for preparing rice starch with a high content of resistant starch according to claim 2, wherein In step 2, the mass volume ratio of hyaluronic acid, carboxylated Fe3O4 and deionized water is (4-5) mg: (1-3) mg: 1 mL.

5. The method for preparing rice starch with a high content of resistant starch according to claim 2, wherein In the step 4, the mass volume ratio of the Fe3O4@hyaluronic acid magnetic porous gel to the polylysine solution is 1 g:(10-50) mL.

6. The method for preparing rice starch with a high content of resistant starch according to claim 1, wherein In step S2, the mass volume ratio of the polylysine-Fe3O4@hyaluronic acid magnetic porous gel to the rice milk is 1 g: (100-200) mL.

7. The method for preparing rice starch with a high content of resistant starch according to claim 1, wherein In step S3, the material-liquid ratio of rice starch to water is 1 g:(3-5) mL.

8. The method for preparing rice starch with a high content of resistant starch according to claim 1, wherein: The gradient microwave treatment in step S3 is three-stage, the first stage is 700-800W, 95-100°C for 2-5min; the second stage is 400-600W, 70-80°C for 20-40min; the third stage is 200-250W, 50-60°C for 10-20min.

9. The method for preparing rice starch with a high content of resistant starch according to claim 1, wherein: The low-temperature aging conditions in step S3 are 4° C. and low-speed stirring at 100-150 rpm for 24-48 hours.

10. Rice starch with a high content of resistant starch prepared according to the preparation method according to any one of claims 1 to 9.

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