Preparation method of Chinese yam RS3 type resistant starch

Abstract

The invention provides a preparation method of Chinese yam RS3 type resistant starch, and belongs to the field of functional starch preparation. The method comprises the following steps: firstly dissolving extracted Chinese yam starch, then adding different contents of Chinese yam non-starch polysaccharides in the dissolving process, and uniformly stirring to obtain a mixture solution of the Chinese yam non-starch polysaccharides and the Chinese yam starch. And finally, cooling the mixture solution to room temperature, and retrogradation to obtain the Chinese yam RS3 type resistant starch. According to the method, freezing is originally introduced into a temperature circulation storage process, and meanwhile, Chinese yam non-starch polysaccharide is added into Chinese yam starch to jointly promote formation of a starch enrichment area, so that in the subsequent refrigeration process, moisture redistribution of a starch sample is accelerated, starch retrogradation is promoted, and the content of Chinese yam RS3 type resistant starch is increased; the food can be used as a functional food for relieving postprandial blood sugar rise in a non-treatment manner, and has a wide prospect; meanwhile, the preparation method is simple, free of chemical reagent residues, environmentally friendly and safe, and a new thought is provided for deep processing of Chinese yams.

Description

Technical Field

[0001] The present invention relates to the field of functional starch preparation, in particular to a method for preparing yam RS3 type resistant starch. Background Art

[0002] Starch is a major source of food in the human diet. Based on its digestion rate, starch can be divided into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Starch retrogradation is a common phenomenon in starchy foods during thermal processing. It is affected by factors such as temperature and non-starch components. Retrograded starch, also known as type III resistant starch (RS3), has dietary fiber-like properties and can effectively reduce postprandial blood glucose levels in the elderly and pregnant women. Non-starch polysaccharides, known for their environmental friendliness, are widely used to regulate the retrogradation properties of starchy foods. Starch retrogradation can be viewed as a temperature-dependent, three-step process: crystal nucleation, growth, and maturation. Studies have shown that 4°C promotes crystal nucleation but not crystal growth, while 25°C is detrimental to crystal nucleation but beneficial for crystal growth. Temperature cycling between 4°C and 25°C may induce the gradual nucleation and growth of crystals, thereby promoting the growth of crystalline regions and the refinement of crystallites, thereby altering the RS3 content in cereal starch pastes. However, the temperature cycles between 4°C and 25°C have significant differences in the retrogradation of starch from different sources (such as corn, potato, and cassava), and targeted optimization is required.

[0003] Chinese yam, a member of the Dioscorea genus of the Dioscoreaceae family, has been consumed in my country for thousands of years and is a traditional Chinese medicinal herb with both medicinal and edible properties. Non-starch polysaccharides are one of its main components. Potatoes are the fourth most important food crop after rice, wheat, and corn, and potato starch (PS) accounts for approximately 50–85% of their dry weight. Asymmetrical flow field-flow fractionation (AF4) is a chromatographic-like technique. The absence of a stationary phase in the AF4 cell reduces the risk of sample degradation during the separation process and offers advantages for detecting starch retrogradation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing yam RS3 type resistant starch. The present invention introduces freezing into temperature cycle storage for the first time, and at the same time combines yam non-starch polysaccharides to synchronously increase the RS3 content of yam starch and enhance its functional value.

[0005] The present invention is achieved in that:

[0006] A method for preparing yam RS3 type resistant starch comprises the following steps:

[0007] (a) Peeling the yam, adding NaHSO3 solution to pulp, and sieving to obtain a slurry;

[0008] (b) allowing the slurry obtained in step (a) to stand, discarding the supernatant, and washing and drying the precipitate to obtain crude yam starch;

[0009] (c) adding NaOH solution to the crude yam starch obtained in step (b), stirring, allowing to stand, discarding the supernatant, washing the precipitate, and drying to obtain yam starch;

[0010] (d) weighing defatted yam powder, adding water to mix, performing ultrasonic-assisted hot water extraction, cooling, and centrifuging to remove yam residue;

[0011] (e) adding Sevag reagent to the supernatant obtained in step (d), shaking, standing, removing the precipitate, concentrating, ethanol precipitation, and freeze-drying to obtain yam non-starch polysaccharide;

[0012] (f) dissolving the yam starch obtained in step (c) and adding the yam non-starch polysaccharide obtained in step (e), stirring evenly to obtain a yam non-starch polysaccharide + yam starch mixture solution;

[0013] (g) cooling the mixture solution obtained in step (f) to room temperature, and obtaining yam RS3 type resistant starch after retrogradation.

[0014] Preferably, the amount of the yam non-starch polysaccharide added in step (f) is 10% to 15% of the mass of the yam starch.

[0015] Preferably, the regeneration temperature in step (g) is 4 / -20°C (under temperature cycle storage conditions, each temperature is cycled and stored for 24 hours), and the regeneration time is 6 to 14 days.

[0016] Preferably, in step (f), the dissolution temperature of the yam starch is 78° C., and the dissolution time is 2 h.

[0017] Preferably, in step (d), ultrasound-assisted hot water extraction is carried out, specifically: placing it in a 70° C. water bath, ultrasonic power 200 W, and extraction for 50 minutes.

[0018] Preferably, in step (e), the concentration is specifically: concentrating the supernatant by rotary evaporation to 10% of the original volume.

[0019] The present invention relates to a method for preparing yam RS3 resistant starch based on temperature cycling storage combined with yam non-starch polysaccharides. The method first dissolves extracted yam starch granules, then adds varying amounts of yam non-starch polysaccharides during the dissolution process. After uniform stirring, a mixture of yam non-starch polysaccharides and yam starch is obtained. Finally, the mixture is cooled to room temperature and retrograded to obtain yam RS3 resistant starch.

[0020] The present invention ingeniously introduces freezing into the temperature cycle storage process, and at the same time adds yam non-starch polysaccharides to yam starch, which jointly promotes the formation of starch-enriched areas, accelerates the water redistribution of the starch sample during the subsequent refrigeration process, promotes starch retrogradation, and increases the content of RS3 resistant starch in yam. It can be used as a functional food for non-therapeutic purposes to slow down the rise in postprandial blood sugar, and has broad prospects. At the same time, the preparation method of the present invention is simple, has no chemical reagent residue, is environmentally friendly and safe, and provides a new idea for the deep processing of yam. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the effect of retrogradation of a mixture of yam non-starch polysaccharide and potato starch using the methods of Comparative Examples 1 and 2.

[0022] Figure 2 The effect of retrogradation of a mixture of yam non-starch polysaccharide and yam starch by using the methods of Comparative Examples 3 to 6 and Example 1 is shown.

[0023] Figure 3 The effect of retrogradation of a mixture of yam non-starch polysaccharide and yam starch by the methods of Comparative Examples 7-8 and Examples 1-2 is shown.

[0024] Figure 4 The effect of retrogradation of a mixture of yam non-starch polysaccharide and yam starch by the methods of Comparative Examples 9-10, Example 1 and Example 3 is shown.

[0025] Figure 5 The effect of retrogradation of a mixture of yam non-starch polysaccharide and yam starch by the methods of Comparative Examples 11-12, Example 2 and Example 4 is shown.

[0026] Figure 6 The X-ray diffraction patterns of the mixture of yam non-starch polysaccharide + yam starch stored at 4 / -20°C for 14 days are shown in Comparative Example 13, Comparative Example 14, Example 5 and Example 6. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the following examples. The following examples are only for illustration and are not intended to limit the scope of protection of the present invention in any way.

[0028] The processes and methods not described in detail in the following examples are conventional methods known in the art. The reagents used in the examples are all analytically pure and commercially available or prepared by methods well known to those skilled in the art. The following examples all achieve the purpose of the present invention.

[0029] In the following examples, during the study of yam, experiments were conducted using potato as a control.

[0030] The following method was used to prepare yam starch (YS) and potato starch (PS): yam and potato were washed, peeled and cut into 1 cm 3 Small pieces of YS and PS were added with 0.1% (m / v) NaHSO3 solution and ground in a blender. The slurry was passed through 80- and 200-mesh sieves, transferred to a 2L glass beaker, and allowed to stand for 3 hours. The supernatant was discarded. The precipitate was washed three times with ultrapure water and dried to obtain crude YS and PS. Accurately weigh 10.0g of crude YS and PS, add 150mL of 0.18% (m / v) NaOH solution, stir at 40°C for 2 hours (300 rpm), and collect the white precipitate below. After washing three times with 50% (v / v) ethanol and water, the YS and PS were dried.

[0031] Yam non-starch polysaccharide (YNSP) was prepared using the following method: 10.0 g of defatted yam powder was weighed and placed in a 500 mL beaker. 300 mL of ultrapure water was added. The mixture was then placed in a 70°C water bath and ultrasonically extracted at 200 W for 50 min. After extraction, the mixture was cooled to room temperature and the supernatant was collected by centrifugation. The supernatant was then added to a 200 mL Erlenmeyer flask with Sevag reagent (chloroform:n-butanol = 4:1) in a 4:1 ratio and shaken thoroughly for 10 min. After shaking, the mixture was transferred to a separatory funnel and allowed to stand for 10 min. The lower precipitate was discarded, and the supernatant was concentrated by rotary evaporation, precipitated with alcohol, and freeze-dried to obtain YNSP.

[0032] Retrograded samples of YNSP+YS mixtures were prepared using the following method: 30.0, 28.5, 27.0, and 25.5 mg of YS were weighed into 20 mL sample vials, 1.5 mL of 1 mol / L NaOH solution was added, and the mixture was stirred at 200 rpm for 6 min at room temperature. The mixture was stirred at 400 rpm in a 78°C water bath for 4 min. 7.0 mL of deionized water was added and stirring continued for 1.5 h. Subsequently, 0, 1.5, 3.0, and 4.5 mg of YNSP were added and stirring continued for 30 min. These samples were designated as YS, 5% YNSP+YS, 10% YNSP+YS, and 15% YNSP+YS, respectively. Finally, 1.5 mL of 1 mol / L HCl solution was added to neutralize the pH and stirring continued for 1 min to obtain 3 mg / mL starch solutions. The starch solutions were divided into five groups and stored at 4, 25, -20, 4 / 25, and 4 / -20°C for 0 to 14 days. 4 / 25 and 4 / -20℃ refer to storage under two temperature cycle conditions, with each temperature being stored for 24 hours in sequence.

[0033] Retrograded samples of YNSP+PS mixtures were prepared using the following method: 30.0 and 25.5 mg of PS, respectively, were weighed into 20 mL sample vials, 1.5 mL of 1 mol / L NaOH solution was added, and the mixture was stirred at 200 rpm at room temperature for 6 minutes. The mixture was stirred at 400 rpm in a 78°C water bath for 4 minutes, 7.0 mL of deionized water was added, and stirring was continued for 1.5 hours. Then, 0 and 4.5 mg of YNSP were added, and stirring was continued for 30 minutes. These samples were designated as PS and 15% YNSP+PS. Finally, 1.5 mL of 1 mol / L HCl solution was added to neutralize the pH and stirring was continued for 1 minute to obtain a 3 mg / mL starch solution. The starch solutions were stored at 4 / -20°C for 0 to 14 days (storing at 4°C and -20°C in a cycle of 24 hours at each temperature).

[0034] AF4-dRI was used to detect the retrogradation of starch solution. The carrier liquid used was 5 mM NaNO2 solution (pH = 7). A 350 μm polyester gasket and a 10 kDa regenerable cellulose membrane (RC) were used to form an AF4 long flow channel. The injection volume was 100 μL, the injection concentration was 0.5 mg / mL, the detector flow rate was 1 mL / min, the initial cross-flow flow rate was 1.2 mL / min, and it exponentially decayed to 0.1 mL / min with a half-life of 3.0 min.

[0035] The crystal form of starch samples was characterized by XRD, with a scanning rate of 2° / min and a step size of 0.02° within the range of 4° to 40°.

[0036] Comparative Example 1

[0037] PS solutions stored for 14 days under 4 / -20°C temperature cycling were analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier solution. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0038] Comparative Example 2

[0039] A 15% YNSP + PS mixture solution was analyzed after 14 days of temperature cycling at 4 / -20°C, using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0040] The test results obtained in Comparative Examples 1 to 2 are as follows: Figure 1 In order to investigate the effect of YNSP on PS retrogradation under 4 / -20℃ temperature cycle storage, YNSP was mixed with PS at a concentration of 15%. Figure 1 It can be seen that the AF4-dRI signal intensity of 15% YNSP+PS is higher than that of PS, indicating that the addition of YNSP inhibits PS retrogradation.

[0041] Comparative Example 3

[0042] A 10% YNSP + YS mixture stored at 4°C for 14 days was analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0043] Comparative Example 4

[0044] A 10% YNSP + YS mixture stored at 25°C for 14 days was analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0045] Comparative Example 5

[0046] A 10% YNSP + YS mixture stored at -20°C for 14 days was analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0047] Comparative Example 6

[0048] A 10% YNSP + YS mixture solution stored at 4 / 25°C for 14 days was analyzed using a 5 mM NaNO₂ solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0049] Example 1

[0050] A 10% YNSP + YS mixture solution was analyzed after 14 days of temperature cycling at 4 / -20°C using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0051] The test results obtained in Comparative Examples 3 to 6 and Example 1 are as follows Figure 2 As shown. Since dRI is a concentration detector, the absorption peak intensity is related to the concentration of the sample. Figure 2 It can be seen that the AF4-dRI signal intensity is lowest when the storage temperature is 4 / -20°C, indicating that the degree of retrogradation of the 10% YNSP+YS mixture is the highest under 4 / -20°C cyclic storage. This may be because when the starch solution is stored at -20°C, water molecules freeze into ice crystals, restricting the movement of starch molecules. The formation of ice crystals concentrates YNSP+YS molecules in adjacent areas, forming starch-enriched areas. During subsequent storage at 4°C, water redistribution is accelerated, promoting the retrogradation of the 10% YNSP+YS mixture.

[0052] Comparative Example 7

[0053] YS solutions stored for 14 days under a 4 / -20°C temperature cycle were analyzed using a 5 mM NaNO₂ solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0054] Comparative Example 8

[0055] A 5% YNSP + YS mixture solution was analyzed after 14 days of storage in a 4 / -20°C temperature cycle using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0056] Example 2

[0057] A 15% YNSP + YS mixture solution was analyzed after 14 days of temperature cycling at 4 / -20°C. The carrier solution was 5 mM NaNO2 (pH 7). AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0058] The test results obtained in Comparative Examples 7-8 and Examples 1-2 are as follows Figure 3 In order to investigate the effect of YNSP content on YS retrogradation under 4 / -20℃ temperature cycle storage, YNSP was mixed with YS at concentrations of 5%, 10% and 15%. Figure 3 It can be seen that the AF4-dRI signal intensity of YS gradually decreases with the increase of YNSP content. This shows that within the concentration range of 5% to 15%, YNSP promotes YS regeneration in a concentration-dependent manner. Figure 1 The results showed opposite effects, indicating that YNSP has different effects on the retrogradation of different starch types. The higher the YNSP content, the easier it is to compete with amylopectin for water molecules. Together with the 4 / -20℃ temperature cycle storage, it affects the water redistribution of the starch solution and promotes YS retrogradation.

[0059] Comparative Example 9

[0060] A 10% YNSP + YS mixture solution was analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier solution. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0061] Comparative Example 10

[0062] A 10% YNSP + YS mixture solution was analyzed after 2 days of temperature cycling at 4 / -20°C. The carrier solution was 5 mM NaNO2 (pH 7). AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0063] Example 3

[0064] A 10% YNSP + YS mixture solution was analyzed after 6 days of temperature cycling at 4 / -20°C using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0065] The test results obtained in Comparative Examples 9-10, Example 1 and Example 3 are as follows Figure 4 As shown. Figure 4 As can be seen, the AF4-dRI signal of the 10% YNSP+YS mixture gradually decreased with the extension of storage time. When the storage time increased to 6 days, the AF4-dRI signal of amylose and amylopectin decreased significantly, indicating that the 10% YNSP+YS mixture had undergone significant retrogradation.

[0066] Comparative Example 11

[0067] A 15% YNSP + YS mixture solution was analyzed using a 5 mM NaNO2 solution (pH 7) as the carrier. AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0068] Comparative Example 12

[0069] A 15% YNSP + YS mixture solution was analyzed after 2 days of temperature cycling at 4 / -20°C. The carrier solution was 5 mM NaNO2 (pH 7). AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0070] Example 4

[0071] A 15% YNSP + YS mixture solution was analyzed after 6 days of temperature cycling at 4 / -20°C. The carrier solution was 5 mM NaNO2 (pH 7). AF4 separation conditions were: 100 μL injection volume, 0.5 mg / mL injection concentration, 1.0 mL / min detector flow rate, an initial crossflow rate of 1.2 mL / min exponentially decaying to 0.1 mL / min, and a half-life of 3.0 min.

[0072] The test results obtained in Comparative Examples 11 to 12, Example 2 and Example 4 are as follows Figure 5 As shown. Figure 5 As can be seen, the AF4-dRI signal of the 15% YNSP+YS mixture gradually decreased with the extension of storage time. When the storage time increased to 6 days, the AF4-dRI signal of amylose and amylopectin decreased significantly, indicating that the 15% YNSP+YS mixture had undergone significant retrogradation.

[0073] Comparative Example 13

[0074] After 14 days of storage in a 4 / -20°C temperature cycle, the YS solution was dialyzed for 12 hours and then freeze-dried to obtain YS powder. This powder was characterized for crystal form and analyzed for relative crystallinity. Scans were performed over a range of 4° to 40° at a scan rate of 2° / min and a step size of 0.02°.

[0075] Comparative Example 14

[0076] A 5% YNSP+YS solution stored in a 4 / -20°C temperature cycle for 14 days was dialyzed for 12 hours and then freeze-dried to obtain a 5% YNSP+YS mixture powder. This powder was characterized for crystal form and analyzed for relative crystallinity. Scans were performed over a range of 4° to 40° at a scan rate of 2° / min and a step size of 0.02°.

[0077] Example 5

[0078] A 10% YNSP+YS solution stored for 14 days at 4 / -20°C was dialyzed for 12 hours and then freeze-dried to obtain a 10% YNSP+YS mixture powder. This powder was subjected to crystal form characterization and relative crystallinity analysis. Scanning was performed over a range of 4° to 40° at a scan rate of 2° / min and a step size of 0.02°.

[0079] Example 6

[0080] A 15% YNSP+YS solution stored for 14 days at 4 / -20°C was dialyzed for 12 hours and then freeze-dried to obtain a 15% YNSP+YS mixture powder. This powder was characterized for crystal form and analyzed for relative crystallinity. Scans were performed over a range of 4° to 40° at a scan rate of 2° / min and a step size of 0.02°.

[0081] The test results obtained in Comparative Examples 13-14 and Examples 5-6 are as follows Figure 6 As shown. Figure 6 It can be seen that with the increase of YNSP content, the relative crystallinity of the YNSP+YS mixture gradually increased, indicating that the YNSP+YS mixture underwent obvious retrogradation, which once again proved that YNSP promoted the retrogradation of YS in a concentration-dependent manner.

Claims

1. A method for preparing yam RS3 type resistant starch, characterized in that: The steps include: a. Peel the yam, add NaHSO3 solution and beat it, then sieve to obtain a slurry; b. After the slurry obtained in step a is allowed to stand, the supernatant is discarded, and the precipitate is washed and dried to obtain crude yam starch; c. Add NaOH solution to the crude yam starch obtained in step b, stir, let stand, discard the supernatant, wash and dry the precipitate to obtain yam starch; d. Weigh defatted yam powder, add water to mix, extract with ultrasonic-assisted hot water, cool and centrifuge to remove yam residue; e. Adding Sevag reagent to the supernatant obtained in step d, shaking, standing, removing the precipitate, concentrating, ethanol precipitation, and freeze-drying to obtain yam non-starch polysaccharide; f. Dissolve the yam starch obtained in step c, then add the yam non-starch polysaccharide obtained in step e, and stir evenly to obtain a yam non-starch polysaccharide + yam starch mixture solution; g. Cooling the mixture solution obtained in step f to room temperature, and obtaining yam RS3 type resistant starch after retrogradation.

2. The method for preparing yam RS3 type resistant starch according to claim 1, wherein: In step f, the amount of yam non-starch polysaccharide added is 10% to 15% of the mass of yam starch.

3. The method for preparing the yam RS3 type resistant starch according to claim 1, wherein: In step g, the regeneration temperature is 4°C and -20°C, and the storage is cycled between 4°C and -20°C for 24 hours, resulting in a regeneration time of 6 to 14 days.

4. The method for preparing yam RS3 type resistant starch according to claim 1, wherein: In step f, the yam starch is dissolved in a NaOH solution and heated in a water bath to dissolve.

5. The method for preparing yam RS3 type resistant starch according to claim 4, wherein: In step f, after adding the yam non-starch polysaccharide obtained in step e, heating in a water bath is continued, and finally HCl solution is added for neutralization.

6. The method for preparing yam RS3 type resistant starch according to claim 4, wherein: In step f, the water bath heating temperature is 78°C.

7. The method for preparing yam RS3 type resistant starch according to claim 1, wherein: In step d, ultrasonic-assisted hot water extraction is performed, specifically: placing it in a 70°C water bath, ultrasonic power 200 W, and extraction for 50 min.

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