Preparation method of low-digestion red rice starch

Abstract

The invention discloses a preparation method of low-digestion red rice starch, and belongs to the technical field of starch modification. The preparation method of the low-digestion red rice starch comprises the following steps: extracting starch in red rice, crushing and sieving to obtain red rice native starch with the volume average diameter of 4.58 + / -0.03 mu m; the preparation method comprises the following steps: treating red rice native starch, then carrying out vacuum freeze drying, crushing and sieving to obtain debranched starch with the volume average diameter of 36.00 + / -3.05 [mu] m; and adjusting the moisture content of the debranched starch, balancing in a sealed container at room temperature, carrying out heating reaction, repeating the step 2-3 times, and crushing and sieving to obtain the low-digestion red rice starch with the volume average diameter of 1506.07 + / -85.05 mu m. The RS content in the low-digestion red rice starch prepared by the method is obviously increased from 8.26% to 34.85%, and is increased by 3.22 times. Meanwhile, the low-digestibility red rice starch prepared by the method has the advantages of low hydrolysis rate, low digestibility, small postprandial blood sugar fluctuation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of starch modification, and particularly relates to a method for preparing low-digestible red rice starch. Background Art

[0002] With the continuous improvement of the living standards of residents in our country, functional rice has gradually become the focus of people's attention. Especially colored rice, due to its unique nutritional value and functional characteristics, has become a hot topic in the research field. In the Yunnan region, with its unique plateau geographical environment, a large number of high-quality colored rice varieties with plateau characteristics have been widely cultivated. Among these rare rice varieties, "Red Rice from Hani Terraces in Honghe" is a gem among rice, mainly distributed in the Hani terrace area with excellent ecological environment, providing unique conditions for the high-quality growth of rice.

[0003] The main carbohydrate in rice is starch, and the starch content in red rice ranges from 74.73% to 78.59%. The digestion mode of starch directly affects the body's energy absorption and metabolism. When starch is rapidly digested in the human intestine, it can cause a sharp increase in blood sugar levels, which may then induce inflammation, oxidative stress reactions, and a decrease in insulin sensitivity. These physiological changes are closely related to the risk of chronic diseases. In view of this, regulating the digestion characteristics of starch has become an important topic in the field of starch research in recent years. At the initial stage of the digestion process, starch digestive enzymes first need to attach to the surface of starch granules, and then gradually diffuse into the granule interior to gradually decompose the starch by hydrolyzing glycosidic bonds. It can be seen that the particle size and surface morphology of starch granules have a significant impact on the entire digestion process; and the current research on preparing low-digestible red rice starch by changing the starch granule size has not been reported. Therefore, it is necessary to provide a method for preparing low-digestible red rice starch to solve the above technical problems. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for preparing low-digestible red rice starch to solve the above technical problems existing in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for preparing low-digestible red rice starch, comprising the following steps:

[0007] (1) Crushing and sieving red rice raw materials to obtain red rice powder;

[0008] (2) Adding a solvent to the red rice powder in step (1) for soaking, and after the soaking ends, volatilizing the solvent to obtain defatted red rice powder;

[0009] (3) Add an alkali solution to the degreased red rice powder in step (2), stir and react, and then let it stand; after standing, perform centrifugal separation to discard the supernatant to obtain precipitate A;

[0010] (4) Wash precipitate A in step (3) with an alkali solution 2 - 3 times, and collect the white starch layer; add deionized water to the white starch layer, adjust the pH value after mixing the white starch layer and deionized water, and then perform centrifugal separation to discard the supernatant to obtain precipitate B;

[0011] (5) Wash precipitate B in step (4) with deionized water 2 - 3 times and then dry it to obtain dried precipitate B; grind the dried precipitate B and then sieve it to obtain raw red rice starch; the volume - average diameter of the raw red rice starch is 4.58 ± 0.03 μm;

[0012] (6) Suspend the raw red rice starch in step (5) in a buffer solution to prepare a 5% raw red rice starch suspension, perform a boiling - water bath on the raw red rice starch suspension, cool it after the boiling - water bath, and add an enzyme for incubation; after incubation, perform a boiling - water bath to inactivate the enzyme, cool it to room temperature and then age it; after aging, perform freeze - drying, pulverize it, and sieve it to obtain debranched starch (the volume - average diameter is 36.00 ± 3.05 μm).

[0013] (7) Measure the water content of the debranched starch in step (6) and adjust its moisture content to 30 - 35%, to obtain water - containing debranched starch; place the water - containing debranched starch in a sealed container and equilibrate it at room temperature for 20 - 25 h; after equilibration, perform heating to obtain heat - treated red rice starch; cool the heat - treated red rice starch to room temperature and then dry it, grind it, and repeat the above process 2 - 3 times to obtain low - digestible red rice modified starch. The volume - average diameter of the low - digestible red rice modified starch is 1506.07 ± 85.05 μm.

[0014] Based on this, this preparation method can increase the volume - average diameter of the red rice raw material powder from 4.58 ± 0.03 μm to 1506.07 ± 85.05 μm (low - digestible red rice modified starch). By increasing the starch particle size, low - digestible red rice modified starch is prepared, increasing the content of resistant starch (RS) in red rice starch, thereby slowing down its hydrolysis rate during the digestion process, reducing the digestive properties of red rice starch, and making it more in line with health requirements.

[0015] Preferably, the mesh number of sieving in step (1) is 100 - 120 meshes.

[0016] Preferably, the solvent in step (2) is petroleum ether; the mass - to - volume ratio of the red rice powder to petroleum ether is 1:2 - 3 g / mL; the soaking time is 2 - 3 h. The method for volatilizing the solvent is to let it stand after soaking, pour out the petroleum ether supernatant after standing, and then let it volatilize naturally in a fume hood.

[0017] Preferably, the lye in step (3) is a 0.2-0.3% NaOH solution; the material-liquid ratio of the defatted red rice powder to the lye is 1:5-6 g / mL; the stirring reaction time is 4-5 h to fully dissolve the protein in the lye; standing is carried out at 3-5 °C for 10-12 h; centrifugal separation is carried out at 4000 - 5000 r / min for 10-12 min.

[0018] Preferably, the lye in step (4) is a 0.2-0.3% NaOH solution; the mass-volume ratio of the white starch layer to deionized water is 1:2-3 g / mL; the pH value is adjusted to 6.5-7.0 using 4-6 mol / L hydrochloric acid.

[0019] Preferably, the drying temperature in step (5) is 40-50 °C; the sieve mesh number is 100-120 meshes. Wash with deionized water 2-3 times until the pH is neutral.

[0020] Preferably, the buffer solution in step (6) is a 50 mM sodium acetate buffer solution with a pH value of 5.0; the boiling water bath time is 15-20 min; cooling is to cool to 50-60 °C.

[0021] Preferably, the enzyme in step (6) is pullulanase; the dosage of the pullulanase is 20 - 25 ASPU / g dry starch; the boiling water bath time is 10-15 min; the cooling temperature is 50-60 °C; the incubation is carried out at 50-60 °C for 6-8 h; the aging is carried out at 4-5 °C for 20-25 h.

[0022] Preferably, the freeze-drying in step (6) is carried out at -40 to -80 °C for 40-50 h; the sieve mesh number for sieving is 100-120 meshes.

[0023] Preferably, the heating in step (7) is carried out at 100-105 °C for 3 - 4 h; drying is carried out at 40-50 °C for 20-25 h; after grinding, sieve through a 100-120 mesh sieve.

[0024] Based on this, this preparation method can increase the volume average diameter of the red rice raw material powder from 4.58 ± 0.03 μm to 1506.07 ± 85.05 μm (low-digestible red rice modified starch). By increasing the starch particle size, low-digestible red rice modified starch is prepared, increasing the content of resistant starch (RS) in red rice starch, thereby slowing down its hydrolysis rate during the digestion process, reducing the digestion characteristics of red rice starch, and making it more in line with health requirements.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The preparation method of the present invention prepares low-digestible red rice starch by increasing the starch particle size to increase the content of resistant starch (RS) in red rice starch. The obtained low-digestible red rice starch has the advantages of low hydrolysis rate, low digestibility, and small postprandial blood glucose fluctuations. Moreover, the preparation method has the advantages of being simple and easy to control, green and safe, and having simple equipment, being suitable for industrial production, and being safe and pollution-free during production.

[0027] 2. The preparation method of the present invention can achieve the synergistic regulation of starch properties, more effectively increase the RS content, significantly improve the digestion characteristics of red rice starch, and show great potential in industrial production.

[0028] 3. The content of RS in the red rice modified starch prepared by this method is significantly increased, and it shows great potential in the application of low-GI foods. Brief Description of the Drawings

[0029] Figure 1 Field emission scanning electron microscope images of RN, RE, RH, and REH;

[0030] Figure 2 Enzymatic hydrolysis first-order kinetic fitting curves of RN, RE, RH, and REH;

[0031] Figure 3 Glucose release levels in vivo at different times after BALB / c mice were fed the samples. Detailed Embodiments

[0032] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0033] Example 1

[0034] The red rice raw materials were ground and passed through a 120-mesh sieve (0.125 mm) to improve the extraction efficiency. Subsequently, they were soaked in petroleum ether for defatting for 2 h. The mass-volume ratio of the red rice raw material powder to petroleum ether was 1:2 g / mL. After the solvent had completely evaporated, a 0.2% NaOH solution was added at a solid-liquid ratio of 1:5 (w / v), and magnetic stirring was carried out for 4 h. Then, it was left to stand at 4 °C for 12 h to allow the proteins to dissolve fully in the 0.2% NaOH solution. After centrifugation (4000 r / min, 10 min), the supernatant was discarded, and the precipitate was washed twice with 0.2% NaOH. The white starch layer was collected, mixed with water, neutralized to pH 6.5 with 5 mol / L dilute hydrochloric acid, and then centrifuged. The neutralized starch was washed three times with distilled water and dried in an oven at 45 °C, and then ground in a mortar to reduce the particles to 120 mesh to obtain raw red rice starch (RN), without any modification treatment.

[0035] Example 2

[0036] The raw red rice starch was suspended in a sodium acetate buffer solution (50 mM, pH 5.0) to prepare a 5% (w / v) starch suspension. Then, it was placed in a boiling water bath for 15 min, cooled to 55 °C, and pullulanase (20 ASPU / g dry starch) was added. It was incubated at 55 °C for 6 h, inactivated by boiling water bath for 10 min, cooled to room temperature, aged at 4 °C for 24 h, freeze-dried at -60 °C for 45 h, pulverized, and passed through a 120-mesh sieve to obtain debranched red rice starch (RE).

[0037] Example 3

[0038] The moisture content of the raw red rice starch was measured and adjusted to 30%. After thorough mixing, it was sealed in a reaction kettle and equilibrated at room temperature for 24 h, and then heated in an electrothermal blast drying oven at 100 °C for 3 h. After heating, the heat-treated starch sample was cooled to room temperature, dried in an electrothermal blast drying oven at 45 °C for 24 h, ground, and passed through a 120-mesh sieve. The above process was repeated to obtain modified red rice starch (RH).

[0039] Example 4

[0040] The moisture content of RE was measured and adjusted to 30%. After thorough mixing, it was sealed in a reaction kettle and equilibrated at room temperature for 24 h, and then heated in an electrothermal blast drying oven at 100 °C for 3 h. After heating, the heat-treated starch sample was cooled to room temperature, dried in an electrothermal blast drying oven at 45 °C for 24 h, ground, and passed through a 120-mesh sieve. The above process was repeated to obtain composite modified red rice starch (REH).

[0041] (1) Granule size determination: The granule size of the starch sample was analyzed using a laser particle size distribution analyzer. Water was used as the dispersant, and the obscuration was set at 10%-15%. The refractive indices of starch and water were set at 1.53 and 1.33, respectively. D[4,3] represents the volume average diameter, and the particle size results are shown in Table 1. Compared with the red rice native starch, the particle size of the low-digestible red rice starch increased significantly (p<0.05).

[0042] Table 1 Volume average diameter D[4,3] in RN, RE, RH, and REH

[0043] Example number Sample D[4,3] (μm) 1 RN <![CDATA[4.58±0.03 a > 2 RE <![CDATA[36.00±3.05 a > 3 RH <![CDATA[39.07±1.43 a > 4 REH <![CDATA[1506.67±85.05 b >

[0044] Note: Data are expressed as mean ± standard deviation (n≥3). Different letters indicate significant differences in the vertical direction (p<0.05), and a-b are in ascending order.

[0045] (2) Microscopic morphology determination: The microscopic surface structure of the starch was observed using a field emission scanning electron microscope (Nova Nano SEM 450, FEI, USA). After the sample was gold-coated, its microscopic morphology was observed at an acceleration voltage of 5 kV and a magnification of 20,000 times. The microscopic morphologies of the red rice native starch and its modified starches are as Figure 1 shown. Compared with the red rice native starch, the microscopic morphology of the low-digestible red rice starch changed significantly, showing aggregation and a large number of pores, which was consistent with the particle size results.

[0046] (3) Enzymatic hydrolysis kinetics and in vitro digestion characteristics determination: The digestion characteristics of the starch sample were evaluated using a modified Englyst in vitro simulation digestion system. 500 mg of the starch sample to be tested was mixed with 10 mL of 0.5 mol / L sodium acetate buffer (pH 5.2) in a 50 mL centrifuge tube. After vortexing evenly, it was pre-gelatinized in a boiling water bath for 20 min. Subsequently, the pre-gelatinized sample was transferred to a 37 °C constant temperature water bath oscillator and oscillated at 170 rpm for 30 min to reach equilibrium. Then, 10 mL of a complex enzyme solution (containing pancreatin extract and amyloglucosidase) was added. At preset time points (0, 10, 20, 40, 60, 90, 120, 150, 180 min), 0.5 mL of the reaction solution was taken and immediately added to 5 mL of absolute ethanol to terminate the reaction. After centrifugation (10000 rpm, 10 min), the supernatant was collected, and the glucose release was measured using the glucose oxidase method (GOPOD kit) at a wavelength of 505 nm.

[0047] The determination process of the total starch mass (TS) is as follows: The completely digested sample is treated successively in a boiling water bath for 30 minutes and an ice bath for 20 minutes, and then 10 mL of 7 mol / L KOH solution is added. It is left standing at 4 °C for 30 minutes to promote the complete dissolution of starch. Take 0.5 mL of the dissolution solution and mix it with 5 mL of 0.5 mol / L acetic acid, add 50 μL of amyloglucosidase, and hydrolyze it by shaking at 70 °C for 30 minutes. After the reaction ends, take 50 μL of the aliquot and mix it with 950 μL of absolute ethanol to inactivate the enzyme. After centrifugation (10000 rpm, 5 minutes), take the supernatant, and determine the glucose content and calculate the total starch content using the same method. The calculation method for the proportion of different digestion components is as follows: The proportion of different digestion components is calculated as follows:

[0048]

[0049] Among them, G0 represents the content of free glucose originally present in the sample solution before enzymatic hydrolysis; G 20 represents the total glucose content in the supernatant after 20 minutes of digestion; G 120 represents the total glucose content in the supernatant after 120 minutes of digestion; TS is the mass of total starch; 0.9 is the molar mass conversion coefficient between glucose and starch.

[0050] The hydrolysis rate of starch at different time points is calculated according to the following formula:

[0051]

[0052] Among them, G t is the glucose content at time t.

[0053] The analysis of amylase hydrolysis kinetics is carried out according to the method established by Goni et al. The first-order kinetic equation is used to fit the starch digestion curve:

[0054] C t = C ∞ (1 - e -kt ) Equation 7 In the formula: t is the time, min; C t represents the cumulative hydrolysis rate at t minutes; C ∞ is the theoretical maximum hydrolysis rate when the reaction reaches completion; k is the kinetic constant of starch, with the unit of per minute (min -1 ).

[0055] The first-order kinetic fitting curves of RN, RE, RH, and REH are as Figure 2As shown. The contents of RDS, SDS, and RS in RN, RE, RH, and REH are shown in Table 2. Compared with red rice native starch, the RS content of low-digestible red rice starch increased significantly from 8.26% to 34.85% (p < 0.05), and the theoretical maximum hydrolysis rate decreased significantly from 91.35% to 70.10% (p < 0.05).

[0056] Table 2 Digestibility parameters and enzymatic kinetics parameters in RN, RE, RH, and REH

[0057] Example number Sample RDS (%) SDS (%) RS (%) <![CDATA[C ∞ (%)]]> <![CDATA[k(h -1 )]]> 1 RN <![CDATA[53.06±0.73 b > <![CDATA[38.69±1.00 c > <![CDATA[8.26±0.28 a > <![CDATA[91.35±1.23 d > <![CDATA[2.34±0.20 b > 2 RE <![CDATA[52.26±0.71 b > <![CDATA[32.77±0.34 b > <![CDATA[14.97±0.37 c > <![CDATA[85.95±0.54 b > <![CDATA[2.87±0.13 d > 3 RH <![CDATA[52.78±0.32 b > <![CDATA[35.46±1.07 b > <![CDATA[11.77±0.76 b > <![CDATA[87.83±1.31 c > <![CDATA[2.48±0.18 c > 4 REH <![CDATA[43.49±2.79 a > <![CDATA[21.66±2.67 a > <![CDATA[34.85±0.74 d > <![CDATA[70.10±1.22 a > <![CDATA[2.23±0.17 a >

[0058] Note: Data are expressed as mean ± standard deviation (n ≥ 3). Different letters indicate significant differences vertically (p < 0.05), with a - d in ascending order from small to large.[[ID=X]] [[ID=X]]

[0059] (4) Measurement of postprandial blood glucose response: The measurement of postprandial blood glucose response was determined by referring to the glucose tolerance test in mice, which can reflect the in vivo digestibility of starch. Mice were separately housed in an approved experimental animal facility with light control (12 h dark, 12 h light) for a 5-day adaptation period. After fasting for 16 hours (without water restriction), mice were orally gavaged with a starch sample solution or a glucose solution (7.5% w / v). Starting from the time of administering the sample solution, tail vein blood samples of each mouse were collected at different time points (0, 30, 60, 90, 120 minutes), and their blood glucose content was measured using a blood glucose meter and blood glucose test strips, and a curve of the glucose concentration in mice over time was plotted based on this. Based on the glucose tolerance test in mice, the in vivo digestibility of starch was determined. Mice were separately housed in an approved experimental animal facility with light control (12 h dark, 12 h light) for a 5-day adaptation period. Mice were fasted without water restriction for 16 h and then orally gavaged with the sample solution. Blood samples were collected from the tail vein of each mouse at different times, and the blood glucose content in mice was measured using a blood glucose meter, and a curve of the glucose release level in mice over time was plotted, as Figure 3 shown. Compared with glucose and RN, the maximum blood glucose concentration of low-digestible red rice starch is lower, and the blood glucose fluctuation is smaller. This characteristic makes it convenient for application in low-GI foods and health products.

[0060] Example 5

[0061] The red rice raw materials were ground and passed through a 110-mesh sieve to improve the extraction efficiency. Subsequently, they were defatted by soaking in petroleum ether for 2.5 h. The mass-volume ratio of the red rice raw material powder to petroleum ether was 1:3 g / mL. After the solvent had completely volatilized, a 0.3% NaOH solution was added at a solid-liquid ratio of 1:6 (w / v), and magnetic stirring was carried out for 5 h. Then, it was left standing at 5 °C for 10 h to allow the proteins to fully dissolve in the 0.3% NaOH solution. After centrifugation (5000 r / min, 11 min), the supernatant was discarded, and the precipitate was washed twice with 0.3% NaOH. The white starch layer was collected, mixed with water, neutralized to pH 6.8 with 4 mol / L dilute hydrochloric acid, and then centrifuged. The neutralized starch was washed twice with distilled water and dried in an oven at 50 °C, and then ground in a mortar to reduce the particle size to 110 mesh to obtain native red rice starch.

[0062] The native red rice starch was suspended in a sodium acetate buffer solution (50 mM, pH 5.0) to prepare a 5% (w / v) starch suspension. Then, it was subjected to a boiling water bath for 18 min, cooled to 50 °C, and pullulanase (25 ASPU / g dry starch) was added. Incubation was carried out at 50 °C for 8 h, followed by a 10-min boiling water bath to inactivate the enzyme. After cooling to room temperature, it was aged at 4 °C for 25 h, freeze-dried at -40 °C for 50 h, pulverized, and passed through a 110-mesh sieve to obtain debranched red rice starch.

[0063] The moisture content of the debranched red rice starch was measured and adjusted to 30%. After thorough mixing, it was sealed in a reaction kettle and equilibrated at room temperature for 25 h, and then heated in an electric blast drying oven at 100 °C for 4 h. After heating, the heat-treated starch sample was cooled to room temperature, dried in an electric blast drying oven at 50 °C for 20 h, ground, and passed through a 110-mesh sieve, and the above process was repeated once to obtain red rice composite modified starch.

[0064] Example 6

[0065] The red rice raw materials were ground and passed through a 100-mesh sieve to improve the extraction efficiency. Subsequently, they were defatted by soaking in petroleum ether for 3 h. The mass-volume ratio of the red rice raw material powder to petroleum ether was 1:2.5 g / mL. After the solvent had completely volatilized, a 0.25% NaOH solution was added at a solid-liquid ratio of 1:5 (w / v), and magnetic stirring was carried out for 4 h. Then, it was left standing at 3 °C for 11 h to allow the proteins to fully dissolve in the 0.25% NaOH solution. After centrifugation (4500 r / min, 10 min), the supernatant was discarded, and the precipitate was washed twice with 0.25% NaOH. The white starch layer was collected, mixed with water, neutralized to pH 7.0 with 6 mol / L dilute hydrochloric acid, and then centrifuged. The neutralized starch was washed three times with distilled water and dried in an oven at 40 °C, and then ground in a mortar to reduce the particle size to 120 mesh to obtain native red rice starch without any modification treatment.

[0066] Red rice starch was suspended in sodium acetate buffer solution (50 mM, pH 5.0) to prepare a 5% (w / v) starch suspension, then boiled in a water bath for 20 min, cooled to 60°C, pullulanase (23 ASPU / g dry starch) was added, incubated at 60°C for 7 h, boiled in a water bath for 10 min to inactivate the enzyme, cooled to room temperature, aged at 5°C for 20 h, freeze-dried at -80°C for 40 h, crushed, and passed through a 100-mesh sieve to obtain red rice debranched starch.

[0067] The moisture content of debranched red rice starch was measured and adjusted to 30%. After thorough mixing, the starch was sealed in a reactor and equilibrated at room temperature for 20 hours. The starch was then heated in an electric forced-air drying oven at 105°C for 4 hours. After heating, the heat-treated starch sample was cooled to room temperature and dried in an electric forced-air drying oven at 40°C for 25 hours. The starch was then ground and passed through a 100-mesh sieve. This process was repeated twice to obtain the red rice composite modified starch.

[0068] The red rice composite modified starch prepared in the above-mentioned Examples 5 and 6 also has the aforementioned effects.

[0069] The above detailed description of the specific embodiments of the invention is intended to be illustrative only, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of the present invention. Therefore, equivalent changes, modifications, and improvements made without departing from the spirit and scope of the present invention are also encompassed within the scope of the present invention.

Claims

1. A preparation method of low-digestible red rice starch, characterized in that, It includes the following steps: (1) Crush and sieve the red rice raw materials to obtain red rice powder; (2) Add a solvent to the red rice powder in step (1) for soaking. After the soaking is completed, let the solvent volatilize to obtain defatted red rice powder; (3) Add an alkali solution to the defatted red rice powder in step (2), stir and react, and then let it stand; after standing, perform centrifugal separation to discard the supernatant to obtain precipitate A; (4) Wash precipitate A in step (3) with an alkali solution 2 - 3 times, and collect the white starch layer; add deionized water to the white starch layer. After mixing the white starch layer and deionized water, adjust the pH value and then perform centrifugal separation to discard the supernatant to obtain precipitate B; (5) Wash precipitate B in step (4) with deionized water 2 - 3 times and then dry it to obtain dried precipitate B; grind the dried precipitate B and sieve it to obtain raw red rice starch; (6) Suspend the raw red rice starch in step (5) in a buffer solution to prepare a 5% raw red rice starch suspension. Perform a boiling water bath on the raw red rice starch suspension. After the boiling water bath is completed, cool it and add an enzyme for incubation; after incubation, perform a boiling water bath to inactivate the enzyme and cool it to room temperature for aging; after aging, perform freeze - drying, grinding, and sieving to obtain debranched starch; (7) Measure the water content of the debranched starch in step (6) and adjust its water content to 30 - 35% to obtain hydrated debranched starch; place the hydrated debranched starch in a sealed container and equilibrate it at room temperature for 20 - 25 h; after equilibration, perform heating to obtain heat - treated red rice starch; cool the heat - treated red rice starch to room temperature and then dry it, grind it, and repeat the above process 2 - 3 times to obtain low - digestible red rice modified starch.

2. The preparation method of the low-digestible red rice starch according to claim 1, wherein, The sieve mesh number in step (1) is 100 - 120 meshes.

3. The preparation method of the low-digestible red rice starch according to claim 1, wherein, The solvent in step (2) is petroleum ether; the mass - to - volume ratio of the red rice powder to petroleum ether is 1:2 - 3 g / mL; the soaking time is 2 - 3 h.

4. The preparation method of the low-digestible red rice starch according to claim 1, characterized in that, The alkali solution in step (3) is a 0.2 - 0.3% NaOH solution; the material - to - liquid ratio of the defatted red rice powder to the alkali solution is 1:5 - 6 g / mL; the stirring reaction time is 4 - 5 h; the standing is at 3 - 5°C for 10 - 12 h; the centrifugal separation is at 4000 - 5000 r / min for 10 - 12 min.

5. The preparation method of the low-digestible red rice starch according to claim 1, wherein, The alkali solution in step (4) is a 0.2 - 0.3% NaOH solution; the mass - to - volume ratio of the white starch layer to deionized water is 1:2 - 3 g / mL; the pH value is adjusted to 6.5 - 7.0 using 4 - 6 mol / L hydrochloric acid.

6. The preparation method of the low-digestible red rice starch according to claim 1, wherein, The drying temperature in step (5) is 40 - 50°C; the sieve mesh number is 100 - 120 meshes.

7. The preparation method of the low-digestible red rice starch according to claim 1, wherein, The buffer solution in step (6) is a 50 mM sodium acetate buffer solution with a pH value of 5.0; the boiling water bath time is 15 - 20 min; the cooling is to 50 - 60°C.

8. The preparation method of the low-digestible red rice starch according to claim 7, characterized in that, The enzyme described in step (6) is pullulanase; the dosage of the pullulanase is 20 - 25 ASPU / g of dry starch; the time of boiling water bath is 10 - 15 min; the cooling temperature is 50 - 60 °C; the incubation is carried out at 50 - 60 °C for 6 - 8 h; the aging is carried out at 4 - 5 °C for 20 - 25 h.

9. The preparation method of the low-digestible red rice starch according to claim 7, characterized in that, The freeze-drying described in step (6) is carried out at -40 to -80 °C for 40 - 50 h; the mesh number of the sieving is 100 - 120 mesh.

10. The preparation method of the low-digestible red rice starch according to claim 7, characterized in that, The heating described in step (7) is carried out at 100 - 105 °C for 3 - 4 h; the drying is carried out at 40 - 50 °C for 20 - 25 h; after grinding, it is sieved through a 100 - 120 mesh sieve.

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