Rice starch having high content of resistant starch and a method for preparing the same

Abstract

The application provides a rice starch with high content of resistant starch and a preparation method thereof, and a polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added into rice slurry, the positive electricity of the polylysine and the negative electricity of the protein are adsorbed out of rice protein through electrostatic interaction, and higher purity rice starch is extracted through high-speed centrifugation and electrostatic interaction; then, gradient microwave treatment and low-temperature crystallization aging are adopted on the rice starch, and finally, the rice starch with high content of resistant starch is prepared, and the functional value of the rice starch is improved.

Description

Technical Field

[0001] This invention belongs to the field of functional starch preparation technology, specifically relating to a rice starch with high resistant starch content and its preparation method. Background Technology

[0002] Resistant starch cannot be digested or degraded by enzymes in the gastrointestinal tract and has physiological functions similar to dietary fiber. Existing research indicates that resistant starch can be fermented and degraded by intestinal microorganisms in the rectum, regulating the structure of the intestinal microbiota and thus affecting intestinal hormone levels and the physiological functions of the pituitary gland, gonads, and pancreas, thereby exerting effects such as lowering blood sugar and lipids. In recent years, the number of people with hypertension, hyperlipidemia, and hyperglycemia in my country has been increasing. Statistics from the end of 2016 show that the number of people with diabetes in my country has reached nearly 200 million. To control the spread of diabetes in my country and prevent and treat diabetes, it is necessary to start with daily foods and adjust the structure of starch through advanced processing technologies to control its digestibility. This is an important direction for the development of starch products and aligns with the requirements of the "Healthy China 2030" Plan.

[0003] Rice is mainly composed of starch and small amounts of protein, lipids, fiber, minerals, vitamins, and phenolic compounds. Approximately 80% is starch and 8% is protein. Protein can denature under high temperatures or extreme pH conditions, forming complexes with starch that inhibit starch chain rearrangement or crystallization, thus hindering the formation of resistant starch. Therefore, the prerequisite for preparing rice starch with high resistant starch content is to extract high-purity rice starch to avoid impurities interfering with subsequent processing. Currently, the main starch extraction methods are alkaline leaching and enzymatic methods. In alkaline leaching, rice is first soaked in dilute alkali, then 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, removing the clear liquid at the top. The starch emulsion at the bottom is centrifuged and dehydrated to separate the starch. However, starch obtained under alkaline conditions is easily structurally damaged, with higher protein residues. Starch with excessively high protein content is prone to spoilage, as protein reacts with glucose converted from starch to undergo non-enzymatic browning. Furthermore, alkaline leaching has a long production cycle, high cost, and is prone to environmental pollution. Enzymatic methods hydrolyze proteins using proteases, facilitating their separation from starch. This method is non-destructive to rice starch, low-cost, and pollution-free. However, in existing compound enzymatic methods for extracting rice protein to produce rice starch, due to the small size of rice starch granules and the large molecular weight of proteins, some large protein fragments after hydrolysis have a similar specific gravity to some starch granules. During hydrocyclone separation, starch and protein cannot be effectively separated. To reduce the protein content in starch and obtain high-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

[0004] Technical problem to be solved: In view of the above-mentioned problems, the purpose of this invention is to provide a rice starch with high resistant starch content and its preparation method. 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 in conjunction with electrostatic interaction to extract rice starch with higher purity. Then, the rice starch is subjected to gradient microwave treatment in conjunction with low-temperature crystallization aging to prepare rice starch with high resistant starch content.

[0005] Technical solution: A method for preparing rice starch with high resistant starch content, comprising the following steps:

[0006] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10-15 wt.%.

[0007] S2. Rice starch extraction: Add polylysine-Fe3O4@hyaluronic acid magnetic porous gel to rice slurry, stir evenly, centrifuge at high speed of 8000-10000 rpm for 5-10 min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0008] S3. Preparation of rice starch with high resistant starch content: 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 sedimentation, drying and pulverization to obtain rice starch with high resistant starch content.

[0009] Furthermore, the preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel in step S2 is as follows:

[0010] Step 1: Disperse Fe3O4 powder in 0.1M sodium citrate solution, and sonicate and centrifuge to obtain carboxylated Fe3O4;

[0011] Step 2: Dissolve hyaluronic acid in deionized water, add carboxylated Fe3O4, stir evenly, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel;

[0012] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1-0.2% polylysine solution;

[0013] Step 4: Immerse Fe3O4@hyaluronic acid magnetic porous gel in polylysine solution, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0014] Furthermore, in step 1, the mass-to-volume ratio of Fe3O4 powder to sodium citrate solution is 1g:(10-20)mL.

[0015] Furthermore, in step 2, the mass-to-volume ratio of hyaluronic acid, carboxylated Fe3O4, and deionized water is (4-5) mg:(1-3) mg:1 mL.

[0016] Furthermore, in step 4, the mass-to-volume ratio of Fe3O4@hyaluronic acid magnetic porous gel to polylysine solution is 1g:(10-50)mL.

[0017] Furthermore, in step S2, the mass-to-volume ratio of polylysine-Fe3O4@hyaluronic acid magnetic porous gel to rice slurry is 1g:(100-200)mL.

[0018] Furthermore, in step S3, the ratio of rice starch to water is 1g:(3-5)mL.

[0019] Furthermore, the gradient microwave treatment in step S3 is a three-stage process: the first stage is 700-800W, 95-100℃ for 2-5 minutes; the second stage is 400-600W, 70-80℃ for 20-40 minutes; and the third stage is 200-250W, 50-60℃ for 10-20 minutes.

[0020] Furthermore, the low-temperature aging conditions in step S3 are 4°C and low-speed stirring at 100-150 rpm for 24-48 hours.

[0021] The rice starch prepared by the above method has a high content of resistant starch.

[0022] Beneficial effects:

[0023] 1. This 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 hyaluronic acid hydrogel to form covalent bonds. Combined with the positive charge of polylysine and the negative charge of hyaluronic acid, the modification of polylysine on the surface and pore walls of hyaluronic acid magnetic porous gel is finally achieved.

[0024] 2. This invention adds polylysine-Fe3O4@hyaluronic acid magnetic porous gel to rice slurry. Unfermented rice slurry is usually close to neutral (pH about 6-7), and the protein pI is 5.6. At this time, pH>pI, and the protein is negatively charged. The polylysine on the magnetic porous gel is positively charged under neutral conditions. Through electrostatic interaction, some rice protein that cannot be separated from starch can be adsorbed. In addition, after adding the magnetic porous gel, the rice slurry is centrifuged at high speed. The strong centrifugal force generated by high-speed centrifugation will accelerate the sedimentation of the gel and at the same time promote more frequent collisions and contact between the protein in the rice slurry and the gel. This dynamic process can promote adsorption to a greater extent. Therefore, through high-speed centrifugation combined with electrostatic interaction, more efficient and low-cost protein separation can be achieved to obtain rice starch with higher purity.

[0025] 3. In this invention, after the magnetic porous gel adsorbs protein, the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel can be separated under the action of an external magnetic field. After removing the protein on the magnetic gel, it can be reused, achieving efficient recycling and reuse.

[0026] 4. This invention employs gradient microwave treatment combined with low-temperature crystallization aging to prepare rice starch with high resistant starch content. Conventional microwave treatment typically uses single power and short processing time, but it often lacks a retrogradation stage, resulting in low resistant starch formation. This invention uses gradient microwave treatment, which is divided into three stages: the first stage is a high-temperature short-time microwave stage, which rapidly destroys the starch granule structure, promoting gelatinization and the release of amylose; the second stage is a medium-temperature maintenance microwave stage, which causes partial breakage and recombination of starch chains; the third stage is a low-temperature polarized microwave stage, which promotes the ordering of functional groups (such as hydroxyl groups), laying the foundation for subsequent crystallization. Then, the microwave-treated starch suspension is rapidly cooled to 4°C and aged by low-speed stirring, which promotes molecular chain rearrangement to form a highly crystalline structure. The low-temperature treatment promotes the recombination of free amylose molecules through hydrogen bonds to form a double helix structure (i.e., retrogradation), thereby forming resistant starch. The synergistic effect of these two processes significantly increases the resistant starch content, ultimately producing functional rice starch. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0028] Example 1

[0029] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0030] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0031] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution;

[0032] Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution at a mass-to-volume ratio of 1g:10mL, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0033] Example 2

[0034] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0035] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0036] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution;

[0037] Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution at a mass-to-volume ratio of 1g:20mL, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0038] Example 3

[0039] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0040] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0041] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution;

[0042] Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution at a mass-to-volume ratio of 1g:30mL, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0043] Example 4

[0044] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0045] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0046] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution;

[0047] Step 4: Immerse Fe3O4@hyaluronic acid magnetic porous gel in polylysine solution at a mass-to-volume ratio of 1g:40mL, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0048] Example 5

[0049] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0050] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0051] Step 3: Dissolve polylysine in PBS buffer to prepare a 0.1% polylysine solution;

[0052] Step 4: Immerse the Fe3O4@hyaluronic acid magnetic porous gel in a polylysine solution at a mass-to-volume ratio of 1g:50mL, shake to mix, wash and dry to obtain polylysine-Fe3O4@hyaluronic acid magnetic porous gel.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 5 is that polylysine modification was not added, as detailed below:

[0055] The preparation method of polylysine-Fe3O4@hyaluronic acid magnetic porous gel is as follows:

[0056] 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, freeze dry to obtain Fe3O4@hyaluronic acid magnetic porous gel.

[0057] Performance testing:

[0058] (1) Porosity

[0059] Table 1. Porosity of polylysine-Fe3O4@hyaluronic acid magnetic porous gels prepared in Examples 1-5 and Comparative Example 1

[0060] 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

[0061] (2) Protein Adsorption Experiment

[0062] The polylysine-Fe3O4@hyaluronic acid magnetic porous gels prepared in Examples 1-5 and Comparative Example 1 were reacted with 0.1 mg / mL BSA solution in a constant-temperature shaker. After reaching adsorption equilibrium, the supernatant was collected, and the absorbance was measured at 280 nm. The concentration of the remaining protein (C0) was calculated according to the standard curve. e The amount of protein adsorbed can be calculated using the following formula:

[0063] Q = (C0 - C) e )×V / m

[0064] Where Q is the amount of protein adsorbed (mg / g); C0 is the protein concentration before adsorption (mg / mL); C e V represents the protein concentration of the supernatant after adsorption (mg / mL); V represents the initial solution volume (mL); and m represents the mass of the magnetic porous gel (g).

[0065] Table 2. Protein adsorption capacity of polylysine-Fe3O4@hyaluronic acid magnetic porous gels prepared in Examples 1-5 and Comparative Example 1.

[0066]

[0067] Based on the porosity in Table 1 and the protein adsorption amount in Table 2, it can be seen that the protein adsorption performance can be improved by utilizing the porous structure and the polylysine modification of the magnetic porous gel. However, the protein adsorption amount of the magnetic porous gel prepared in Comparative Example 1 without polylysine modification is significantly reduced. Therefore, Example 5 was selected for the subsequent preparation of rice starch with high resistant starch content.

[0068] Example 6

[0069] A method for preparing rice starch with high resistant starch content includes the following steps:

[0070] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0071] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 100mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0072] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0073] Example 7

[0074] A method for preparing rice starch with high resistant starch content includes the following steps:

[0075] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0076] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 120mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0077] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0078] Example 8

[0079] A method for preparing rice starch with high resistant starch content includes the following steps:

[0080] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0081] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0082] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0083] Example 9

[0084] A method for preparing rice starch with high resistant starch content includes the following steps:

[0085] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0086] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 180mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0087] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0088] Example 10

[0089] A method for preparing rice starch with high resistant starch content includes the following steps:

[0090] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0091] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 200mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0092] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0093] Example 11

[0094] A method for preparing rice starch with high resistant starch content includes the following steps:

[0095] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0096] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0097] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 800W at 100℃ for 4min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at low speed at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle, dried, and pulverized to obtain rice starch with high resistant starch content.

[0098] Example 12

[0099] A method for preparing rice starch with high resistant starch content includes the following steps:

[0100] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0101] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0102] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 600W at 70℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0103] Example 13

[0104] A method for preparing rice starch with high resistant starch content includes the following steps:

[0105] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0106] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0107] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 250W at 60℃ for 10min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle, dried, and pulverized to obtain rice starch with high resistant starch content.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Example 8 is that polylysine-Fe3O4@hyaluronic acid magnetic porous gel was not added. Specifically, a method for preparing rice starch with high resistant starch content includes the following steps:

[0110] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0111] S2. Rice starch extraction: The rice slurry was centrifuged at 10,000 rpm for 5 minutes to obtain the supernatant and precipitate. After drying the precipitate, high-purity rice starch was obtained.

[0112] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 8 is that it uses the polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Comparative Example 1, as detailed below:

[0115] A method for preparing rice starch with high resistant starch content includes the following steps:

[0116] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0117] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Comparative Example 1 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0118] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Example 8 is that high-speed centrifugation was not used, as detailed below:

[0121] A method for preparing rice starch with high resistant starch content includes the following steps:

[0122] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0123] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, and use an external magnetic field to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel. Separate the precipitate, dry it and you will get high-purity rice starch.

[0124] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0125] Comparative Example 5

[0126] The difference between this comparative example and Example 8 is that it is first centrifuged at high speed, and then polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added, as detailed below:

[0127] A method for preparing rice starch with high resistant starch content includes the following steps:

[0128] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0129] S2. Rice starch extraction: Centrifuge 150 mL of rice slurry at 10000 rpm for 5 min, remove the supernatant, add an appropriate amount of water to the precipitate and add 1 g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5, stir evenly, apply an external magnetic field to the precipitate, and separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel. After drying the remaining precipitate, high-purity rice starch is obtained.

[0130] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. The mixture was then stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle the sediment, dried, and pulverized to obtain rice starch with high resistant starch content.

[0131] Comparative Example 6

[0132] The difference between this comparative example and Example 8 is that gradient microwaves were not used; only single microwaves were used, as detailed below:

[0133] A method for preparing rice starch with high resistant starch content includes the following steps:

[0134] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0135] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0136] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water are mixed at a material-to-liquid ratio of 1g:4mL. After stirring evenly to form a suspension, the mixture is microwaved at 800W for 10min, stirred at 4℃ and 100rpm for 24h, centrifuged, washed with water to settle, dried, and pulverized to obtain rice starch with high resistant starch content.

[0137] Comparative Example 7

[0138] The difference between this comparative example and Example 8 is that low-temperature aging was not used, as detailed below:

[0139] A method for preparing rice starch with high resistant starch content includes the following steps:

[0140] S1. Raw material processing: Rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice flour. Water is added and mixed evenly to obtain rice slurry with a concentration of 10 wt.%.

[0141] S2. Rice starch extraction: Add 1g of polylysine-Fe3O4@hyaluronic acid magnetic porous gel prepared in Example 5 to 150mL of rice slurry, stir evenly, centrifuge at 10000rpm for 5min, remove the supernatant, apply an external magnetic field to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel, and dry the remaining precipitate to obtain high-purity rice starch;

[0142] S3. Preparation of rice starch with high resistant starch content: High-purity rice starch and water were mixed at a material-to-liquid ratio of 1g:4mL. After stirring to form a suspension, the mixture was subjected to gradient microwave treatment. The first stage was 700W at 95℃ for 3min; the second stage was 500W at 75℃ for 30min; and the third stage was 200W at 50℃ for 15min. After centrifugation, washing, sedimentation, drying, and pulverization, rice starch with high resistant starch content was obtained.

[0143] Performance testing:

[0144] (1) Starch purity

[0145] The purity of the rice starch obtained in Examples 6-13 and Comparative Examples 2-7 was determined using the Megazyme reagent kit method.

[0146] Table 3. Purity of rice starch prepared in Examples 6-13 and Comparative Examples 2-7

[0147] 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

[0148] As shown in Table 3, the purity of the rice starch extracted in the examples was 98.18-99.67%. However, in Comparative Example 2, without the addition of polylysine-Fe3O4@hyaluronic acid magnetic porous gel, the purity of the rice starch decreased after high-speed centrifugation alone. Comparative Example 3 used the magnetic porous gel prepared in Comparative Example 1 without modifying polylysine, which reduced the ability to remove rice protein and thus the purity of the starch. Comparative Example 4 did not use high-speed centrifugation, but only used polylysine-Fe3O4@hyaluronic acid magnetic porous gel to adsorb rice protein. The electrostatic adsorption effect is limited, so the purity of the rice starch also decreased. Comparative Example 5 first centrifuged at high speed and then added the gel, which could not achieve the promoting effect of high-speed centrifugation on gel adsorption in the examples, and the purity of the rice starch decreased slightly. Comparative Example 6 did not undergo gradient microwave treatment, and Comparative Example 7 did not use low-temperature aging, so there was no significant impact on the purity of the rice starch. Therefore, it can be seen that the present invention uses high-speed centrifugation combined 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 high resistant starch content.

[0149] (2) Resistant starch content

[0150] Methods for determining the content of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS): Take 1g of rice starch with high resistant starch content prepared in Examples 6-13 and Comparative Examples 2-7, place it in a centrifuge tube, add 10mL of distilled water, boil for 15min, and continuously shake to mix during the water bath process. Then cool in a 37℃ water bath. Add 10mL of pH 1.5 HCl-KCl buffer solution and mix well. Then add 2.8mL of... Mix 0.1 g / mL pepsin solution and incubate at 37°C with shaking in a water bath for 1 hour. Adjust the pH to neutral. Add 10 mL of 0.2 mol / L sodium acetate buffer (pH 5.2) and mix well. Add 5 mL of a mixed enzyme solution of porcine pancreatic α-amylase and amyloglucosidase. Incubate at 37°C with shaking for 0, 20, and 120 minutes. After hydrolysis, aspirate 0.2 mL of the hydrolysate and inactivate the enzyme in a boiling water bath for 5 minutes. Dilute the hydrolysate with distilled water according to the estimated glucose content. Centrifuge at 8000 rpm for 10 minutes. Take 2 mL of the supernatant and determine the glucose content at 510 nm using the DNS method for reducing sugar determination. The contents of slowly digestible starch (SDS), rapidly digestible starch (RDS), and resistant starch (RS) are calculated as follows:

[0151] SDS% = (G120 - G20) × 0.9 / W

[0152] RDS% = (G20 - FG) × 0.9 / W

[0153] RS% = (W - SDS - RDS) / W

[0154] In the formula: G20, the amount of glucose produced after starch hydrolysis for 20 min (mg); G120, the amount of glucose produced after starch hydrolysis for 120 min (mg); FG, the free glucose content before enzymatic hydrolysis; W, the total starch (mg).

[0155] Table 4. Resistant starch content of rice starch prepared in Examples 6-13 and Comparative Examples 2-7

[0156]

[0157]

[0158] As shown in Table 4, the resistant starch content of the rice starch prepared in the embodiments of the present invention is 26.22-29.86%. In contrast, the low purity of the rice starch prepared in Comparative Examples 2-4 interfered with the subsequent processing of high-resistant starch. In Comparative Example 5, the resistant starch content was lower than in the embodiments due to high-speed centrifugation followed by gelation. In Comparative Example 6, the rice starch was not treated with gradient microwaves. Conventional microwave treatment typically uses single power and short processing time, but it often lacks a retrogradation stage, resulting in low resistant starch formation. In Comparative Example 7, the resistant starch content was significantly lower than in the embodiments because low-speed stirring and aging promotes molecular chain rearrangement to form a highly crystalline structure, while low-temperature treatment promotes the reassociation of free amylose molecules through hydrogen bonds to form a double helix structure (i.e., retrogradation), thereby forming resistant starch. Therefore, it is evident that the synergistic treatment of rice starch with gradient microwaves and low-temperature aging in the present invention is more conducive to the formation of resistant starch.

[0159] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing rice starch having a high content of resistant starch, characterized by, Comprising the following steps: S1. Raw material processing: rice is soaked in water, wet-milled, dried, and passed through a 100-mesh sieve to obtain rice powder, which is mixed with water to obtain rice slurry with a concentration of 10-15 wt.%; S2. Rice starch extraction: polylysine-Fe3O4@hyaluronic acid magnetic porous gel is added to the rice slurry, stirred uniformly, and centrifuged at a speed of 8000-10000 rpm for 5-10 min. After removing the supernatant, a magnetic field is applied to the precipitate to separate the complex of rice protein and polylysine-Fe3O4@hyaluronic acid magnetic porous gel. The remaining precipitate is dried to obtain high-purity rice starch; S3. Preparation of rice starch with high content of resistant starch: high-purity rice starch is mixed with water to form a suspension, which is subjected to gradient microwave treatment, low-temperature aging, centrifugation, water washing and precipitation, drying, and crushing to obtain rice starch with high content of resistant starch; The gradient microwave treatment is three-stage, the first stage is 700-800 W, 95-100℃ for 2-5 min; the second stage is 400-600 W, 70-80℃ for 20-40 min; the third stage is 200-250 W, 50-60℃ for 10-20 min.

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

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

4. The process for preparing rice starch having high content of resistant starch according to claim 2, characterized in that, The mass-volume ratio of hyaluronic acid, carboxylated Fe3O4, and deionized water in step 2 is (4-5) mg:(1-3) mg:1 mL.

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

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

7. The method for preparing rice starch with high resistant starch content according to claim 1, characterized in that, The solid-liquid ratio of rice starch to water in step S3 is 1 g:(3-5) mL.

8. The process for preparing rice starch with high content of resistant starch as claimed in claim 1, wherein: The low-temperature aging conditions in step S3 are 4℃, 100-150 rpm low-speed stirring for 24-48 h.

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