Iron stick yam slowly digestible starch as well as preparation method and application thereof

Abstract

The invention discloses iron stick yam slowly digestible starch as well as a preparation method and application thereof, the preparation method comprises the following steps: S1, obtaining fresh iron stick yam, and treating the iron stick yam to obtain yam starch; s2, preparing starch milk from the Chinese yam starch, and carrying out ultrahigh pressure treatment of stepped pressure boosting on the starch milk to obtain Chinese yam starch gel; and S3, drying, crushing and sieving the Chinese yam starch gel to obtain the slowly digestible starch of the iron stick yam. According to the method, the content of slowly digestible starch can be remarkably increased and can reach 30%-50%; further functional application verification shows that the glycemic index can be reduced from 85 to 54 when 20% of the starch is added into the biscuit. The invention is green and additive-free, has simple process, can be industrially amplified, and is suitable for the field of functional foods for diabetes, metabolic syndrome, sports nutrition and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of food science and engineering technology, in particular to a kind of slowly digestible starch of iron stick yam and its preparation method and application. BACKGROUND

[0002] Functional food refers to food with specific health functions or for the purpose of supplementing vitamins and minerals, which is suitable for specific population and has the function of regulating body function, but not for the purpose of treating diseases, and has no acute, subacute or chronic hazards to human body. Slowly digestible starch (SDS) as a typical functional carbohydrate, due to its slow digestion in the small intestine, can maintain stable postprandial blood glucose, and has significant effect on preventing and controlling chronic diseases such as obesity, diabetes and cardiovascular disease. In addition, SDS can also improve glucose tolerance, reduce blood lipid levels, and can be used as a stable energy-releasing carbohydrate source for athletes, especially endurance athletes.

[0003] Yam is a widely popular traditional medicinal and edible plant, rich in starch, mucoprotein, polyphenol, saponin and other active ingredients. Iron stick yam, as a good variety of yam, has high starch content and rich nutritional value, and has the health functions of improving appetite, regulating blood sugar and improving digestion. However, the digestion speed of natural yam starch is fast, and the postprandial blood glucose response is high, which is not suitable for people with blood sugar control needs. In view of this problem, the development of yam starch products with slow digestion characteristics has become a research hotspot in the field of functional food.

[0004] At present, the main methods to improve the SDS content in starch include physical modification (such as heat treatment, wet heat treatment, microwave treatment), enzymatic modification (such as pullulanase debarking), chemical modification (such as crosslinking, esterification) and composite modification method. However, these methods generally have problems such as complex production process, harsh reaction conditions, high energy consumption or safety controversy, which are difficult to meet the industrial demand of green, efficient and nutrient retention. SUMMARY

[0005] In view of the above problems, the present application aims to provide a kind of slowly digestible starch of iron stick yam and its preparation method and application.

[0006] The technical scheme of the present application is as follows: On the one hand, a preparation method of slowly digestible starch of iron stick yam is provided, comprising the following steps: S1: obtaining fresh iron stick yam and treating it to obtain yam starch; S2: using the yam starch to prepare starch milk, and performing step-by-step pressure increase ultrahigh pressure treatment on the starch milk to obtain yam starch gel; S3: The yam starch gel is dried, pulverized, and sieved to obtain the slow-digesting starch of Chinese yam.

[0007] Preferably, in step S1, the fresh iron yam is a fresh raw material that is free from mechanical damage, insect infestation, mold, and rot.

[0008] Preferably, step S1 includes the following sub-steps: washing, peeling, dicing, grinding, filtering, sedimentation, resuspending, drying, pulverizing, and sieving the Chinese yam in sequence.

[0009] Preferably, in step S2, the solvent for the starch milk is deionized water, and the content of the deionized water is greater than or equal to 70%.

[0010] Preferably, in step S2, the temperature for the ultra-high pressure treatment with stepped pressurization is 28-32℃.

[0011] Preferably, in step S2, the ultra-high pressure treatment with stepped pressurization includes pressure stage one, pressure stage two, and pressure stage three, where the pressure gradually increases.

[0012] Preferably, the pressure of the first pressure stage is 300 MPa, the pressure of the second pressure stage is 450 MPa, and the pressure of the third pressure stage is 600 MPa.

[0013] Preferably, the pressurization rate of each pressure stage is 10 MPa / s, each pressure stage is maintained for 5 minutes, and the depressurization time after ultra-high pressure treatment is less than 2 seconds.

[0014] On the other hand, a method for preparing slow-digesting starch from Dioscorea opposita described in any one of the above-mentioned methods is also provided, along with its application as a functional ingredient in food processing.

[0015] The beneficial effects of this invention are: This invention can significantly improve the slow digestibility of yam starch, and the resulting SDS content can reach 30%-50%. The preparation method of this invention is green and environmentally friendly, simple to operate, and can effectively preserve the original nutrients and flavor of yam. It is suitable for the industrial development of functional foods, and is especially suitable for people with chronic diseases such as diabetes and obesity. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The images are SEM images of natural yam starch and starches from the examples and comparative examples, magnified at 1000× and 5000×. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0019] On the one hand, the present invention provides a method for preparing slow-digesting starch from Chinese yam, comprising the following steps: S1: Obtain fresh Chinese yam and process it to obtain yam starch.

[0020] In one specific embodiment, the fresh iron yam is a fresh raw material that is free from mechanical damage, insect infestation, mold, and rot.

[0021] In one specific embodiment, the processing includes the following sub-steps: washing, peeling, dicing, grinding, filtering, sedimentation, resuspending, sedimentation, drying, pulverizing, and sieving the iron yam in sequence.

[0022] S2: The yam starch is used to prepare starch milk, and the starch milk is subjected to ultra-high pressure treatment with step-up pressure to obtain yam starch gel.

[0023] In one specific embodiment, the solvent of the starch milk is deionized water, and the content of the deionized water is greater than or equal to 70%.

[0024] Ultra-high pressure (UHPP) treatment is a purely physical modification process carried out at room temperature or medium to low temperatures. By subjecting materials to short-term high-pressure conditions of 100-1000 MPa, the molecular structure can be altered without damaging the flavor and nutritional value of the materials. In a specific embodiment, the temperature for the step-up UHPP treatment is 28-32°C, and the step-up UHPP treatment includes three pressure stages with gradually increasing pressure: pressure stage one, pressure stage two, and pressure stage three.

[0025] Optionally, the pressure of the first pressure stage is 300 MPa, the pressure of the second pressure stage is 450 MPa, and the pressure of the third pressure stage is 600 MPa. Optionally, the pressure increase rate of each pressure stage is 10 MPa / s, each pressure stage is maintained for 5 minutes, and the pressure relief time after ultra-high pressure treatment is less than 2 seconds.

[0026] In the above embodiments, for starch milk in a starch-water system, ultra-high pressure treatment can break the hydrogen bonds between starch molecules and promote the entry of water molecules, destroy the microcrystalline structure, and induce the starch molecular chains to rearrange to form a dense structure during cooling, thereby improving its slow digestibility.

[0027] It should be noted that this invention controls the slow-digesting starch content of the obtained starch by adjusting the moisture content in the starch slurry and by applying stepped pressure. In the above embodiments, the moisture content is the content obtained by the inventors through research under different pressure conditions that ensures a slow-digesting starch content greater than 30%. When the moisture content is less than this, it is difficult to obtain a slow-digesting starch content greater than 30% even by adjusting different stepped pressure values. In the above embodiments, the pressure values ​​of each pressure stage are only preferred embodiments. When using this invention, other pressure values ​​can be selected between 200-600 MPa for three-stage pressure adjustments, which can also achieve a slow-digesting starch content greater than 30%.

[0028] S3: The yam starch gel is dried, pulverized, and sieved to obtain the slow-digesting starch of Chinese yam.

[0029] In this invention, by regulating the moisture content and stepwise pressurization in the starch milk, the orderly rearrangement and structural densification of molecular chains can be achieved without damaging the morphology and natural nutrients of yam starch granules. This enables dual structural regulation of the crystalline and amorphous regions, forming a new semi-gelatinized dense network structure, effectively enhancing the resistance to enzymatic hydrolysis, and significantly increasing the content of slowly digestible starch (SDS) by 30%-50%.

[0030] On the other hand, the present invention also provides a slow-digesting starch of Dioscorea opposita prepared by the method described in any one of the above-mentioned methods, and its application as a functional ingredient in food processing.

[0031] Example 1 A slow-digesting starch from Chinese yam is prepared through the following steps: (1) Obtain fresh iron yam, and process it in sequence by washing, peeling, dicing, grinding, filtering, sedimentation, resuspending, sedimentation, drying, crushing and sieving to obtain yam starch; (2) Add the yam starch to deionized water according to the mass fraction, adjust the water content to 70% (w / w), stir evenly, put it into a polypropylene bottle, remove the air, put it into a polypropylene bag, and vacuum seal it with a vacuum sealer to obtain a double-layer packaged starch-water suspension sample. Let it stand overnight to obtain starch milk. (3) The starch milk is placed in an ultra-high pressure device and subjected to ultra-high pressure treatment through a step-by-step pressurization program (300→450→600 MPa segment pressurization, each stage is maintained for 5 min, the pressurization rate is 10 MPa / s, and the treatment temperature is 30±2℃). After depressurization (the depressurization time is less than 2 s), yam starch gel is obtained. (4) After the yam starch gel is balanced for 2 hours, it is filtered, vacuum freeze-dried for 48 hours, pulverized and passed through a 100-mesh sieve to obtain the slow-digesting starch of iron yam, named YS-step-70.

[0032] Example 2 Unlike Example 1, the starch milk in step (2) of this example has a water content of 90% (w / w), and the obtained slow-digesting starch from Chinese yam is named YS-Step-90.

[0033] It should be noted that the above embodiments are only some embodiments of the present invention. The preparation method of the present invention, by changing the parameters such as temperature, time, pressurization rate, and pressure value of ultra-high pressure treatment, can also produce the slow-digesting starch of Dioscorea opposita described in the present invention.

[0034] Comparative Example 1 Unlike Example 1, the starch milk in step (2) of this comparative example has a water content of 20% (w / w), and the obtained slow-digesting starch from Chinese yam is named YS-Step-20.

[0035] Comparative Example 2 Unlike Example 1, the starch milk in step (2) of this comparative example has a water content of 30% (w / w), and the obtained slow-digesting starch from Chinese yam is named YS-Step-30.

[0036] Comparative Example 3 Unlike Example 1, the starch milk in step (2) of this comparative example has a water content of 50% (w / w), and the obtained slow-digesting starch from Chinese yam is named YS-Step-50.

[0037] Comparative Example 4 Unlike Comparative Example 1, in this comparative example, step (3) directly increases the pressure to 600 MPa in one step, and the processing time is 15 min. The slow-digesting starch of Dioscorea opposita obtained is named YS-One-Step-20.

[0038] Comparative Example 5 Unlike Comparative Example 2, in this comparative example, step (3) directly increases the pressure to 600 MPa in one step, and the processing time is 15 min. The slow-digesting starch of Dioscorea opposita obtained is named YS-One-Step-30.

[0039] Comparative Example 6 Unlike Comparative Example 3, in this comparative example step (3), the pressure was directly increased to 600 MPa in one step, and the processing time was 15 min. The slow-digesting starch of Dioscorea opposita obtained was named YS-One-Step-50.

[0040] Comparative Example 7 Unlike Example 1, in this comparative example, step (3) directly increases the pressure to 600 MPa in one step, and the processing time is 15 min. The slow-digesting starch of Dioscorea opposita obtained is named YS-One-Step-70.

[0041] Comparative Example 8 Unlike Example 2, in this comparative example, step (3) directly increases the pressure to 600 MPa in one step, and the processing time is 15 min. The slow-digesting starch of Dioscorea opposita obtained is named YS-One-Step-90.

[0042] Test Example 1 The microstructure of samples obtained in each embodiment and comparative example was observed using scanning electron microscopy (SEM). The method used was to sputter-coat the starch samples with gold and photograph them at 1000× and 5000× magnifications under an accelerating voltage of 15 kV. The test results are as follows. Figure 1 As shown.

[0043] from Figure 1 It can be seen that natural yam starch ( Figure 1 The YS particles are generally oval or oblate, with a smooth surface, intact edges, and no obvious cracks or holes, showing the typical intact structure of natural starch.

[0044] In samples treated with stepwise high pressure (HHP), those treated under low moisture conditions (20–50%) (YS-step-20 / 30 / 50) generally maintained their original morphology, but slight depressions, wrinkles, or fine cracks were observed on the surface of some particles. This indicates that HHP treatment at low moisture levels caused a certain degree of external stress on the starch particles, possibly triggered by rapid moisture compression or internal pressure. As the moisture content increased to 70% and 90%, significant changes occurred in the starch particle structure. The YS-step-90 sample showed obvious cracks, collapses, and even a membrane-like coating structure, indicating that the internal structure of the starch was destroyed under high moisture and high pressure conditions. This may be due to the violent expansion of the particles after absorbing water, leading to the formation of vacuolated particle structures under the action of HHP.

[0045] In samples treated with one-step pressure, those treated under low moisture conditions (20–50%) (YS-One-Step-20 / 30 / 50) showed significant surface damage, such as deep indentations and edge cracking, indicating that the high pressure caused a stronger structural stress response in the particles. Particularly in the YS-One-Step-50 sample, some particles appeared to have adhered and deformed, indicating that particle aggregation or partial gelation had begun. In samples treated with high moisture content under one-step pressure (YS-One-Step-70 / 90), the particles essentially lost their intact structure, exhibiting severe cracking, collapse, or a film-like structure. This demonstrates that high moisture content significantly enhances the compressibility of the particles, causing severe disintegration of the starch structure.

[0046] Test Example 2 The crystal structures of the samples obtained in each embodiment and comparative example were analyzed by X-ray diffraction (XRD). The test conditions were 40 kV and 40 mA, with Cu-Kα as the radiation source, a diffraction scanning angle range of 4° to 60°, a step size of 0.02°, and a scanning speed of 6° / min when the diffraction scanning angle (2θ) was 4° to 60°. The test results are shown in Table 1. Table 1. Relative crystallinity of the samples obtained in Examples 1-5 and Comparative Examples 1-5 and natural yam starch.

[0047] Natural YS exhibits typical C-type crystal characteristics, with diffraction peaks at 2θ≈15°, 17°, 23°, and 26°, consistent with the crystal structure of tuberous starches. These characteristic diffraction peaks persisted even after stepwise pressurization and a single 600 MPa treatment, indicating that the HHP treatment did not alter the crystal structure of YS. However, the peak intensity gradually decreased with increasing pressure and moisture content, suggesting some degree of damage to the crystalline region.

[0048] As shown in Table 1, the relative crystallinity (RC) of natural YS is 15.395%. After ultra-high pressure (HHP) treatment, the RC gradually decreased, from 14.804% (YS-step-20) to 13.058% (YS-step-90) under step-pressure treatment, and decreased more significantly to 11.384% (YS-one-step-90) under a single-step 600 MPa treatment. This trend indicates that under higher pressure and moisture conditions, HHP promotes the migration and rearrangement of starch molecular chains, thereby interfering with the regular stacking of the double helix and causing the crystalline regions to be destroyed.

[0049] Test Example 3 The initial gelatinization temperature (To), peak temperature (Tp), final temperature (Tc), and enthalpy (ΔHg) of the samples obtained from each example and comparative example were determined using differential scanning calorimetry (DSC). The test procedure was as follows: 3 mg of starch suspension was sealed in a standard aluminum dish and equilibrated overnight at room temperature to ensure uniform moisture distribution. Then, the temperature was scanned from 20°C to 100°C at a heating rate of 10°C / min. The test results are shown in Table 2. Table 2 Thermal properties of starch samples and natural yam starch obtained from each example and comparative example

[0050] Note: In Table 2, the superscript letters of the numerical values ​​represent the significance level of the differences between groups.

[0051] As shown in Table 2, all samples exhibited a single endothermic transition, indicating starch gelatinization. Compared to natural YS (To 78.35°C, Tp 80.60°C, Tc 84.75°C), step-pressurization and one-step pressurization at 600 MPa generally resulted in significant increases in To and Tp, especially at higher moisture levels. For example, YS-One-Step-90 exhibited the highest To (83.15°C) and Tp (83.70°C), indicating that more thermal energy is required to initiate and reach peak gelatinization. The increased gelation temperature may be due to rearrangement or densification of starch crystalline regions caused by HHP-induced molecular recombination, as indicated by SEM and XRD results of increased particle compaction and structural heterogeneity. Higher onset and peak temperatures are generally associated with more thermally stable domains or incomplete gelation due to HHP-induced grain enhancement. The ΔHg of natural YS was 5.30 J / g, but it decreased significantly in all treated samples, with YS-Step-90 showing a ΔHg as low as 0.32 J / g. This sharp decrease implies a substantial loss of crystallization sequence and a reduction in the energy required to disrupt the double helix, consistent with the XRD results showing a decrease in relative crystallinity. Notably, the ΔHg value decreased sharply with increasing water content and pressure intensity. For example, the ΔHg of YS-Step-20 was 2.65 J / g, while that of YS-Step-90 dropped to 0.32 J / g. These results suggest that HHP promotes partial gelatinization or disordering, making the starch less heat-resistant. The gelation range (Tc−To) reflects the heterogeneity of the crystals. The range for natural YS was 6.4°C, remaining relatively narrow in most Step-Boost treated samples, but widening to 3.05°C in YS-Step-90, indicating increased heterogeneity. This widening may be due to the coexistence of disrupted and partially ordered domains, in which the less perfect spirals melt at lower temperatures, while the more ordered regions resist thermal deformation.

[0052] Test Example 4 Digestion tests were performed on samples obtained from each example and comparative example. The test procedure was as follows: 100 mg of starch sample was suspended in 7.5 mL of acetate buffer (pH 5.5) and incubated at 40°C for 20 min. While stirring at 250 rpm, 5 mL of enzyme solution containing α-amylase (280 U / mL) and amyloglucosidase (100 U / mL) was added to the suspension to start the reaction. Aliquots (0.1 mL) were collected at 0, 10, 20, 40, 60, 80, 100, 120, 150, and 180 min, and the reaction was terminated by adding 1 mL of ethanol (95%). The reaction mixture was centrifuged at 14000 rpm for 5 min, and the glucose released in the supernatant was measured using a GOPODkit (Megazyme, Ireland). The contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) were determined using the method of Englyst et al., and the test results are shown in Table 3. The contents of total starch and free glucose were designated as T and F, respectively. The glucose contents produced during hydrolysis at 20 min and 120 min were recorded as G. 20 and G 120 The contents of RDS, SDS, and RS are calculated using the following formulas:

[0053]

[0054]

[0055] Table 3. Contents of RDS, SDS, and RS of starch samples and natural yam starch obtained in each example and comparative example.

[0056] Note: In Table 3, the superscript letters of the numerical values ​​represent the significance level of the differences between groups.

[0057] Table 3 shows that the RDS, SDS, and RS contents of natural YS were 6.68%, 7.72%, and 85.58%, respectively, indicating that its starch structure is mainly resistant. After treatment with HHP under a step-up pressurization mode, the RDS content increased slightly, the SDS content increased significantly, while the RS gradually decreased as the moisture content increased from 20% to 90%. Specifically, the YS-Step-90 sample showed the highest SDS value (49.03%) and the lowest RS value (40.29%). This trend suggests that under moderate pressure, some structures are disrupted, which may make amorphous regions susceptible to enzymatic attack. In contrast, the samples treated with a one-step pressurization of 600 MPa showed a significantly different pattern. With increasing moisture content, the RDS content increased sharply from 13.46% (YS-Step-20) to 58.45% (YS-600-90), while the RS decreased sharply from 73.74% to only 11.66%. This dose-dependent reduction in digestive resistance can be attributed to more profound changes in the starch granule and molecular structure under high-pressure processing. As previously confirmed by SEM results, the integrity of starch granules is compromised under higher pressure and moisture levels, with visible damage and fragmentation on the surface. Furthermore, XRD analysis showed a persistent decrease in relative crystallinity (RC), particularly at 600 MPa, further supporting the loss of ordered domains, which may be related to increased enzyme sensitivity.

[0058] Application Example 1 In a basic biscuit recipe, 20% YS-Step-90 was used to replace flour. The glycemic index (glycemic index) was measured using an in vitro eGI prediction model, and the results showed that the eGI decreased from 85 to 54. This demonstrates that this invention utilizes a step-pressurization ultra-high pressure treatment to prepare slowly digestible starch, significantly altering the digestibility of YS by adjusting its physicochemical structure. Under the step-pressurization mode, structural damage is limited, and the starch maintains a relatively high RS content. However, under a one-step pressurization to 600 MPa, especially under high humidity conditions, extensive gelation or disruption of the double helix leads to a significant conversion of RS to RDS and SDS. The step-pressurization mode, through gradual pressure changes, causes only localized ordered rearrangement of starch molecules, possibly related to the dense gel layer formed on the starch granule surface, which delays α-amylase contact sites. This treatment maintains the SDS content at 30%-50%, significantly higher than the one-step treatment.

[0059] This invention systematically applies ultra-high pressure technology to regulate the slow digestion of yam starch. By adjusting the starch-to-water ratio and the ultra-high pressure boosting program, it achieves dual structural regulation of both the crystalline and amorphous regions, forming a new semi-gelatinized dense network structure and endowing the starch with superior resistance to enzymatic hydrolysis. The prepared slow-digesting yam starch has advantages such as high nutritional value, good safety, and slow absorption. The ultra-high pressure processing equipment used in the preparation method is a common model in the existing food processing industry, requiring no special design or complex supporting equipment, and possesses good industrial compatibility and a foundation for promotion. It should be noted that the ultra-high pressure processing scheme of this invention is also applicable to other plant starches (such as broken rice, corn, sweet potato, peas, etc.), demonstrating good raw material adaptability and providing a new approach for the high-value utilization of various low-value starch resources.

[0060] The above description is merely a representative embodiment of the present invention and is not intended to limit the present invention in any way. Any embodiment made by those skilled in the art without departing from the scope of the present invention and utilizing the disclosed technical content is an equivalent embodiment of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing slow-digesting starch from Dioscorea opposita, characterized in that, Includes the following steps: S1: Obtain fresh Chinese yam and process it to obtain yam starch; S2: The yam starch is used to prepare starch milk, and the starch milk is subjected to ultra-high pressure treatment with step-up pressure to obtain yam starch gel; S3: The yam starch gel is dried, pulverized, and sieved to obtain the slow-digesting starch of Chinese yam.

2. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 1, characterized in that, In step S1, the fresh iron yam is a fresh raw material that is free from mechanical damage, insect infestation, mold, and rot.

3. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 1, characterized in that, Step S1 includes the following sub-steps: washing, peeling, dicing, grinding, filtering, sedimentation, resuspending, sedimentation, drying, pulverizing, and sieving the iron yam in sequence.

4. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 1, characterized in that, In step S2, the solvent for the starch milk is deionized water, and the content of the deionized water is greater than or equal to 70%.

5. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 1, characterized in that, In step S2, the temperature for the ultra-high pressure treatment with stepped pressurization is 28-32℃.

6. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 1 or 5, characterized in that, In step S2, the ultra-high pressure treatment with stepped pressurization includes pressure stage one, pressure stage two, and pressure stage three, where the pressure gradually increases.

7. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 6, characterized in that, The pressure in the first pressure stage is 300 MPa, the pressure in the second pressure stage is 450 MPa, and the pressure in the third pressure stage is 600 MPa.

8. The method for preparing slow-digesting starch from Dioscorea opposita according to claim 6, characterized in that, The pressurization rate for each pressure stage is 10 MPa / s, and each pressure stage is maintained for 5 minutes. The depressurization time after ultra-high pressure treatment is less than 2 seconds.

9. A slow-digesting starch from Chinese yam, characterized in that, It is prepared by the method for preparing slow-digesting starch from Dioscorea opposita according to any one of claims 1-8.

10. The application of the slow-digesting starch of Dioscorea opposita as described in claim 9 as a functional ingredient in food processing.

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