Low-glycemic-index starch and processing method thereof

Abstract

The invention discloses low-glycemic-index starch and a processing method thereof, and belongs to the field of starch modification processing. The preparation method comprises the following steps: adding a proper amount of deionized water into starch to prepare a starch emulsion, uniformly stirring, regulating the pH value to 6.0 by using a citric acid buffer solution, carrying out microwave treatment on the starch emulsion under the condition that the power is 700-900W, regulating the pH value to 6.5 by using the citric acid buffer solution, adding 40000U / g of high-temperature-resistant alpha-amylase, carrying out enzymolysis, and carrying out high-pressure treatment; adjusting the pH value to 5.0 by using a citric acid buffer solution, adding 8U / mL of pullulanase, reacting, and degrading enzyme activity in a high-temperature sterilization pot; and standing, naturally cooling, carrying out low-temperature aging treatment, centrifuging, removing supernatant, dehydrating, drying, crushing and sieving to obtain the low-glycemic-index starch. The influence of starch aging on the food GI index can be fully utilized, and the GI index of the product is reduced. And the production process is simple, low in cost and low in energy consumption. The starch has the characteristics of high resistant starch content and low glycemic index.

Description

Technical Field

[0001] The invention belongs to the field of starch modification and processing, and specifically relates to low glycemic index starch and a preparation method thereof. Background Art

[0002] In recent years, due to the increasing diversity of food types and the unreasonable dietary composition, the energy intake and consumption of the human body are unbalanced, which has led to an increase in the number of people suffering from insulin resistance, diabetes, obesity and other related metabolic syndromes. According to the U.S. Dietary Standards (USDA), carbohydrates are macronutrients that are essential to human health and provide 45% to 65% of the human body's energy needs. Starch is the main storage form of plant carbohydrates and accounts for a large proportion of the human diet. It can provide energy substances necessary for human survival. Its postprandial blood sugar response is significantly positively correlated with the glycemic index (GI). A lower GI means that sugar takes longer to be absorbed into the blood, so it will not fluctuate as much as the blood glucose content. Among them, the content of resistant starch (RS) is linearly negatively correlated with the glycemic index.

[0003] It is reported that there are three methods for preparing resistant starch (RS) and slowly digestible starch (SDS) in starch: (1) chemical method - preparation by esterification reaction with octenyl succinic anhydride (OSA) as reactant; (2) physical method - annealing and wet heat treatment (HMT) method; (3) enzymatic method. Although chemical methods can greatly increase the content of RS and SDS in starch, the treated starch has chemical reagent residues and the product composition is difficult to control; physical methods have problems such as complex operation, high energy consumption, and high production cost. Gurayal et al. used pullulanase to treat rice starch. After debranching and cooling treatment, the RS content in rice starch was significantly increased. Lu et al. used ultrasound combined with enzyme method to treat pea starch and found that the RS content could be increased by combining pullulanase and ultrasound treatment. Chung et al. used toughening and wet heat methods to treat corn, pea, and lentil starch, combining physical and chemical modifications. The results showed that toughening and wet heat treatment can increase the levels of SDS and RS in starch.

[0004] The α-amylase used in the present invention is a food additive that has been evaluated for safety by the Food Safety Standards and Monitoring and Assessment Department, and its quality complies with the "National Food Safety Standard Food Additives Enzyme Preparations for Food Industry" (GB1886.174); the enzyme has the advantages of low price, short enzymolysis time, and low production cost. More importantly, the core institutions such as the United States Department of Agriculture, Purdue University and Iowa State University, Japan and India mostly use enzymolysis methods such as α-amylase to increase the content of resistant starch and slowly digestible starch, and the enzyme is also allowed to be used as an enzyme preparation for the food industry by the United States Food and Drug Administration, the Danish Veterinary and Food Bureau, etc.

[0005] At present, the potato industry in my country focuses on fresh consumption and disease resistance, and neglects the selection and breeding of special varieties such as processing, resulting in a single potato variety. The proportion of special potatoes in China is only about 5%, while in developed countries it is more than 70%. Due to the lack of potato varieties suitable for processing whole flour, fried slices and fried strips, many processing companies have idle equipment and insufficient production, and market demand is mainly met by imports. Potato starch has a high content of resistant starch, which can reduce postprandial blood sugar levels and effectively control the incidence of metabolic chronic diseases such as obesity and diabetes. At present, all kinds of steamed bread on the market (including multi-grain steamed bread) require wheat flour as the main raw material, which has the disadvantages of fast starch digestion rate and high postprandial blood sugar index, and is not suitable for special groups such as diabetics and obese people. Summary of the invention

[0006] The purpose of the present invention is to provide a low glycemic index starch suitable for diabetics. Through the improved enzymatic method combined with toughening and aging processes, the gelatinization of high-chain starch and the debranching of branched starch by high-temperature resistant α-amylase and pullulanase are used to generate more straight-chain starch, and the molecules are recrystallized to generate high-content resistant starch. The low glycemic index starch required by the present invention is one or more of potato starch, rice starch, corn starch or mung bean starch, which has the characteristics of high resistant starch content and low glycemic index, and can meet the dietary needs of special consumers.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a processing method for preparing low-glycemic index starch by hydrolyzing with amylase, and the processing method comprises the following steps:

[0009] 1) Add appropriate amount of deionized water to starch to prepare 10% to 40% starch emulsion;

[0010] 2) stirring the starch emulsion in step 1) uniformly, and adjusting the pH value to 6.0 with a citric acid buffer;

[0011] 3) The starch emulsion in step 2) was subjected to microwave treatment at a power of 700 to 900 W for 100 to 140 s, cooled, adjusted to a pH of 6.5 with a citric acid buffer solution, and added with 40,000 U / g of a thermostable α-amylase, and subjected to enzymolysis at 75° C. for 15 min;

[0012] 4) After enzymatic hydrolysis, take out and perform high pressure treatment at 120°C for 30 minutes;

[0013] 5) After high pressure, take out, adjust the pH value to 5.0 with citric acid buffer, add 8U / mL pullulanase, and react at 60℃ for 24h;

[0014] 6) After the reaction, take out and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes;

[0015] 7) Take out under high pressure, let it stand and cool naturally, perform low-temperature aging treatment, centrifuge, discard the supernatant, dehydrate and dry, crush and sieve to obtain low glycemic index starch.

[0016] In step 1), the starch content in the starch emulsion is 10% to 40%, preferably 15%. The starch is one or more of potato starch, wheat starch, rice starch, corn starch or mung bean starch.

[0017] In step 3), the microwave treatment is carried out at a power of 700 to 900 W and a treatment time of 100 to 140 s.

[0018] In step 7), the standing time is 7 to 8 hours.

[0019] In step 7), the low-temperature aging temperature is 2 to 6 degrees, and the low-temperature aging time is 22 to 26 hours.

[0020] In step 7), the centrifugal speed is 3500-4000 r / min, and the centrifugal time is 10-15 min.

[0021] In step 7), the drying is carried out by hot air drying method, and the drying conditions are: temperature of 35-55° C., wind speed of 2-3 m / s, drying time of 18-24 h, and after drying, the mixture is crushed and passed through a 100-mesh sieve.

[0022] The invention provides a low glycemic index starch, wherein the potato starch is prepared according to the above preparation method.

[0023] The invention provides application of low-glycemic index starch in food for diabetic patients.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] Compared with existing potato starch or other starches, the present invention can fully utilize the influence of starch aging on the GI index of food and further reduce the GI index of the product.

[0026] Application of starch prepared by the method of the present invention in diabetic patients.

[0027] The invention adopts enzyme treatment, microwave toughening and aging methods to treat starch. The starch obtained without chemical treatment is non-toxic and harmless, and the content of resistant starch is significantly increased.

[0028] The production process of the invention is simple, and the involved production equipment is efficient, low in cost, low in energy consumption, easy to clean, and easy to realize industrialized production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the method of the present invention;

[0030] Figure 2 The object of the present invention;

[0031] Figure 3 The RS index comparison between the low glycemic index potato starch and the ordinary potato starch in Example 1 of the present invention;

[0032] Figure 4 The SDS index comparison between the low glycemic index potato starch and the ordinary potato starch in Example 1 of the present invention;

[0033] Figure 5 This is a graph showing changes in postprandial blood sugar in rats after feeding the low glycemic index potato starch and native starch in Example 1. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application are described clearly and completely below. The embodiments are only used to explain the present invention and are not used to limit the scope of the present invention. The experimental methods used in the following embodiments are conventional methods unless otherwise specified; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0035] The method for determining SDS and RS in the low glycemic index starch involved in the embodiment of the present invention is:

[0036] ⑴ Determination method of resistant starch

[0037] The resistant starch (RS) content in potato starch was determined by the enzyme-gravimetric method recommended by the Association of Official Analytical Chemists (AOAC). The specific steps are as follows:

[0038] Take an appropriate amount of the starch, add citric acid buffer, adjust the pH value to 1.5, add pepsin solution, keep constant temperature at 40℃ for 60min, and cool to room temperature; adjust the pH value to 6.0-7.0, add heat-resistant α-amylase solution, keep constant temperature at 90℃ for 30min, cool; adjust the pH value to 4.75, add glucoamylase solution, keep constant temperature at 60℃ for 60min, cool, centrifuge, and discard the supernatant. The precipitate is completely dissolved in 4mol·L-1KOH solution, neutralized with HCl solution, added glucoamylase solution, kept constant temperature at 60℃ for 60min, cooled, centrifuged, and the supernatant is collected, and the volume is made up to 100ml with distilled water, and the content of reducing sugar is determined by 3,5-dinitrosalicylic acid method (DNS).

[0039] The content of resistant starch was calculated according to the following formula:

[0040] RS(%)=100-G(%)×0.9

[0041] In the formula, RS is the content of resistant starch; G is the content of reducing sugar; 0.9 is the conversion coefficient of reducing sugar to starch.

[0042] ⑵ Determination method of slowly digestible starch (SDS):

[0043] Take 100 mg of the starch, add 15 ml of phosphate buffer (0.1 M, pH 6.9), boil in water for 15 min, cool to 37°C, add 10 ml of α-amylase (200 U / ml, 37°C), mix well and immediately place in a 37°C shaker (150 r / min) for incubation for 10 h. The maltose produced by hydrolysis is determined by 3,5-dinitrosalicylic acid method (DNS), and the maltose concentration is calculated according to the maltose standard curve to convert the SDS content.

[0044] The content of slowly digestible starch is calculated according to the following formula:

[0045] SDS=(BA) / C×100%

[0046] Wherein, A is the amount of maltose released after 1 hour of enzymatic hydrolysis of the sample; B is the amount of maltose produced after 10 hours of enzymatic hydrolysis of the sample; C is the total amount of starch (measured in maltose).

[0047] Example 1

[0048] like Figure 1 This embodiment relates to a method for preparing low glycemic index potato starch, comprising the following steps:

[0049] 1) Weigh 100 g of potato starch, add appropriate amount of deionized water and mix thoroughly to prepare a potato starch emulsion;

[0050] 2) stirring the potato starch emulsion in step 1) uniformly, adjusting the pH value to 6.0 with a citric acid buffer, and preparing a 25% potato starch emulsion with deionized water;

[0051] 3) The potato starch emulsion described in 2) was subjected to microwave treatment for 120 s at a power of 900 W, and 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 70° C. for 15 min;

[0052] 4) After enzymatic hydrolysis, take out and perform high pressure treatment at 120°C for 30 minutes;

[0053] 5) After high pressure, take out, adjust the pH value to 5.0 with citric acid buffer, add 8U / mL pullulanase, and react at 60℃ for 24h;

[0054] 6) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 100°C for 10 min;

[0055] 7) After high pressure, take out, cool naturally, place in a refrigerator at 4 degrees, age at low temperature for 24 hours, centrifuge at 4000 r / min for 15 minutes, discard the supernatant, dry with hot air at 55 degrees for 24 hours, grind after drying, and pass through a 100-mesh sieve to obtain low glycemic index potato starch.

[0056] The low glycemic index potato starch prepared in this embodiment is as follows Figure 2 shown.

[0057] Example 2

[0058] This embodiment relates to a method for preparing low glycemic index corn starch, comprising the following steps:

[0059] 1) Weigh 100 g corn starch, add appropriate amount of deionized water and mix thoroughly to prepare corn starch emulsion;

[0060] 2) stirring the corn starch emulsion in step 1) uniformly, adjusting the pH value to 6.0 with citric acid buffer, and preparing a 25% corn starch emulsion with deionized water;

[0061] 3) The corn starch emulsion in step 2) was subjected to microwave treatment at a power of 900 W for 120 s, and 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 70° C. for 15 min;

[0062] 4) After enzymatic hydrolysis, take out and perform high pressure treatment at 120°C for 30 minutes;

[0063] 5) After high pressure, take out, adjust the pH value to 5.0 with citric acid buffer, add 8U / mL pullulanase, and react at 60℃ for 24h;

[0064] 6) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 100°C for 10 min;

[0065] 7) After high pressure, take out, cool naturally, place in a refrigerator at 4 degrees, age at low temperature for 24 hours, centrifuge at 4000 r / min for 15 minutes, discard the supernatant, dry with hot air at 55 degrees for 24 hours, grind after drying, and pass through a 100-mesh sieve to obtain low glycemic index potato starch.

[0066] Example 3

[0067] 1) Take 100g rice starch and add appropriate amount of deionized water to prepare a 10% starch emulsion.

[0068] 2) The pH value of the starch emulsion was adjusted to 6.0 with citric acid buffer.

[0069] 3) The starch emulsion was subjected to microwave treatment at a power of 700 W for 100 s, and then 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 75° C. for 15 min.

[0070] 4) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 120°C for 30 min.

[0071] 5) After the high pressure treatment, the mixture was taken out, the pH value was adjusted to 5.0 with citric acid buffer, 8 U / mL of pullulanase was added, and the mixture was reacted at 60° C. for 24 h.

[0072] 6) After the reaction, take out the mixture and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes.

[0073] 7) After being taken out under high pressure, the mixture is cooled naturally, subjected to low-temperature aging treatment, centrifuged, the supernatant is discarded, the mixture is dehydrated and dried, crushed and sieved to obtain low glycemic index starch.

[0074] Example 4

[0075] 1) Take 100g potato starch and 100g corn starch, add appropriate amount of deionized water, and prepare a 20% starch emulsion.

[0076] 2) The pH value of the starch emulsion was adjusted to 6.0 with citric acid buffer.

[0077] 3) The starch emulsion was subjected to microwave treatment at a power of 800 W for 110 s, and then 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 75° C. for 15 min.

[0078] 4) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 120°C for 30 min.

[0079] 5) After the high pressure treatment, the mixture was taken out, the pH value was adjusted to 5.0 with citric acid buffer, 8 U / mL of pullulanase was added, and the mixture was reacted at 60° C. for 24 h.

[0080] 6) After the reaction, take out the mixture and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes.

[0081] 7) After being taken out under high pressure, the mixture is cooled naturally, subjected to low-temperature aging treatment, centrifuged, the supernatant is discarded, the mixture is dehydrated and dried, crushed and sieved to obtain low glycemic index starch.

[0082] Example 5

[0083] 1) Take 100g potato starch and 200g mung bean starch, add appropriate amount of deionized water, and prepare a 30% starch emulsion.

[0084] 2) The pH value of the starch emulsion was adjusted to 6.0 with citric acid buffer.

[0085] 3) The starch emulsion was subjected to microwave treatment at a power of 850 W for 115 s, and then 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 75° C. for 15 min.

[0086] 4) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 120°C for 30 min.

[0087] 5) After the high pressure treatment, the mixture was taken out, the pH value was adjusted to 5.0 with citric acid buffer, 8 U / mL of pullulanase was added, and the mixture was reacted at 60° C. for 24 h.

[0088] 6) After the reaction, take out the mixture and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes.

[0089] 7) After being taken out under high pressure, the mixture is cooled naturally, subjected to low-temperature aging treatment, centrifuged, the supernatant is discarded, the mixture is dehydrated and dried, crushed and sieved to obtain low glycemic index starch.

[0090] Example 6

[0091] 1) Take 400g of mung bean starch, add appropriate amount of deionized water, and prepare a 40% starch emulsion.

[0092] 2) The pH value of the starch emulsion was adjusted to 6.0 with citric acid buffer.

[0093] 3) The starch emulsion was subjected to microwave treatment at a power of 900 W for 120 s, and then 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 75° C. for 15 min.

[0094] 4) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 120°C for 30 min.

[0095] 5) After the high pressure treatment, the mixture was taken out, the pH value was adjusted to 5.0 with citric acid buffer, 8 U / mL of pullulanase was added, and the mixture was reacted at 60° C. for 24 h.

[0096] 6) After the reaction, take out the mixture and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes.

[0097] 7) After being taken out under high pressure, the mixture is cooled naturally, subjected to low-temperature aging treatment, centrifuged, the supernatant is discarded, the mixture is dehydrated and dried, crushed and sieved to obtain low glycemic index starch.

[0098] Example 7

[0099] 1) Take 500g wheat starch and add appropriate amount of deionized water to prepare a 40% starch emulsion.

[0100] 2) The pH value of the starch emulsion was adjusted to 6.0 with citric acid buffer.

[0101] 3) The starch emulsion was subjected to microwave treatment at a power of 900 W for 120 s, and then 40000 U / g of thermostable α-amylase was added and enzymolysis was performed at 75° C. for 15 min.

[0102] 4) After enzymatic hydrolysis, the product was taken out and subjected to high pressure treatment at 120°C for 30 min.

[0103] 5) After the high pressure treatment, the mixture was taken out, the pH value was adjusted to 5.0 with citric acid buffer, 8 U / mL of pullulanase was added, and the mixture was reacted at 60° C. for 24 h.

[0104] 6) After the reaction, take out the mixture and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes.

[0105] 7) After being taken out under high pressure, the mixture is cooled naturally, subjected to low-temperature aging treatment, centrifuged, the supernatant is discarded, the mixture is dehydrated and dried, crushed and sieved to obtain low glycemic index starch.

[0106] The present invention uses citric acid buffer to adjust the pH value, the purpose of which is to optimize the active environment of the enzyme. Appropriate adjustment of the pH value can improve the enzymatic hydrolysis efficiency. Microwave treatment can quickly heat the starch emulsion to achieve the effect of pre-gelatinization. The selection of power (700-900W) can ensure that the starch granules fully absorb water and gelatinize. Adding high-temperature resistant α-amylase for enzymatic hydrolysis is intended to partially degrade starch molecules. High-pressure treatment further destroys the starch structure and increases the enzymatic hydrolysis efficiency. Adding pullulanase continues to degrade specific bonds in the starch molecules. It helps to further reduce the molecular weight of starch and change its structure. Treatment in a high-temperature sterilizer can effectively inactivate the enzyme and terminate the enzymatic hydrolysis reaction. It ensures that the enzyme activity of the final product will not affect its stability and performance. Low-temperature aging treatment helps to change the crystalline structure of starch and increase the content of resistant starch. Centrifugation removes the supernatant, and dehydration, drying, crushing and sieving are performed to obtain the final product.

[0107] The present invention uses α-amylase and pullulanase in combination to bring more comprehensive and efficient modification effects in starch modification processing. α-amylase mainly acts on the α-1,4 glycosidic bonds of amylose, while pullulanase can specifically hydrolyze the α-1,6 glycosidic bonds in amylopectin. The combined use of the two can achieve a more comprehensive and thorough enzymolysis effect and reduce the molecular weight of the final product. Pullulanase can increase the amorphous region of starch and promote the formation of resistant starch. It helps to improve the health benefits of the final product, especially for applications that require control of blood sugar levels. Starch treated with pullulanase has better solubility and thermal stability. This makes modified starch more flexible and reliable in food processing.

[0108] The present invention can maximize the synergistic effect of the two enzymes through reasonable experimental design and optimization, thereby improving the quality and functionality of the final product.

[0109] Figure 3 is the RS index of the present invention; Figure 3 It can be seen that the resistant starch content of the improved potato starch of the present invention is significantly higher than that of ordinary potato starch. The improved low glycemic index potato starch treated by enzyme treatment, microwave toughening and aging has a higher RS ​​value, which shows that the process of the present invention successfully increases the resistant components in starch.

[0110] Figure 4 is the SDS index of the present invention; the performance of the improved potato starch of the present invention during digestion. The height of each column represents the percentage of the residual starch content of the corresponding starch during digestion. Figure 4 It can be seen that the modified starch of the present invention breaks down more slowly during digestion, thereby resulting in a lower blood sugar response.

[0111] Figure 5 The figure is a time course diagram of the changes in postprandial blood sugar in rats after feeding two different types of potato starch (low glycemic index potato starch and native starch in Example 1) and glucose. The experimental rats were randomly divided into 3 groups: one group was fed with low glycemic index potato starch (modified starch in Example 1), another group was fed with native starch, and another group was fed with glucose as a control group. There were 20 rats in each group. Before the experiment began, the rats fasted for 12 hours to ensure that the blood sugar level was at the basal state. Each group of rats was fed an equal amount of the test substance (low glycemic index potato starch, native starch or glucose). The blood sugar levels of the rats were recorded before and after feeding, and blood samples were collected at different time points to measure blood sugar. Blood sugar levels were measured using a blood glucose meter or a biochemical analyzer. The results are as shown in the figure. Figure 5 As shown, in Figure 5 In the figure, the horizontal axis represents time (min) and the vertical axis represents blood glucose level (in millimoles per liter, mmol / L). Figure 5 It can be seen that after consuming the low glycemic index potato starch of the present invention, the blood sugar level of the rats rises slowly and has a lower peak value. In contrast, after consuming native starch, the blood sugar level of the rats rises faster and has a higher peak value. The experiment shows that the peak blood sugar level of the low glycemic index potato starch group is significantly lower than that of the native starch group and the glucose group. The effect of the improved potato starch of the present invention in reducing postprandial blood sugar response. From the above data, it can be seen that the low glycemic index starch of the present invention can indeed reduce blood sugar levels.

[0112] The improved starch of the present invention is suitable for people who need to control blood sugar levels, such as diabetic patients or people who need a low glycemic index diet. The improved low glycemic index starch of the present invention can be used in diabetic food.

[0113] The present invention can make full use of the effect of starch aging on the GI index of food, and further reduce the GI index of the product. The production process of the present invention is simple, and the production equipment involved is efficient, low in cost, low in energy consumption, easy to clean, and easy to realize industrial production. The starch has the characteristics of high resistant starch content and low glycemic index, and can meet the dietary needs of special consumers.

[0114] Although the present invention has been described in detail above by general description, specific implementation and test, those skilled in the art may make various modifications or improvements on the basis of the present invention without departing from the scope thereof after considering the description and practicing the application disclosed herein. Therefore, the present application is intended to cover any variation, use or adaptive change of the present application, and these modifications or changes made on the basis of not departing from the spirit of the present invention are all within the scope of the present invention.

Claims

1. A method for processing low glycemic index starch, characterized in that The steps include: 1) Add appropriate amount of deionized water to starch to prepare 10% to 40% starch emulsion; 2) stirring the starch emulsion in step 1) uniformly, and adjusting the pH value to 6.0 with a citric acid buffer; 3) The starch emulsion in step 2) was subjected to microwave treatment at a power of 700 to 900 W for 100 to 140 s, cooled, adjusted to a pH of 6.5 with a citric acid buffer solution, and added with 40,000 U / g of a thermostable α-amylase, and subjected to enzymolysis at 75° C. for 15 min; 4) After enzymatic hydrolysis, take out and perform high pressure treatment at 120°C for 30 minutes; 5) After high pressure, take out, adjust the pH value to 5.0 with citric acid buffer, add 8U / mL pullulanase, and react at 60℃ for 24h; 6) After the reaction, take out and degrade the enzyme activity in a high temperature sterilizer at 100°C for 10 minutes; 7) Take out under high pressure, let it stand and cool naturally, perform low-temperature aging treatment, centrifuge, discard the supernatant, dehydrate and dry, crush and sieve to obtain low glycemic index starch.

2. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 1), the starch content in the starch emulsion is 10% to 40%, preferably 15%.

3. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 1), the starch is one or more of potato starch, wheat starch, rice starch, corn starch or mung bean starch.

4. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 3), the microwave treatment is carried out at a power of 700 to 900 W and a treatment time of 100 to 140 s.

5. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 7), the standing time is 7 to 8 hours.

6. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 7), the low-temperature aging temperature is 2 to 6 degrees, and the low-temperature aging time is 22 to 26 hours.

7. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 7), the centrifugal speed is 3500-4000 r / min, and the centrifugal time is 10-15 min.

8. A method for processing low glycemic index starch as claimed in claim 1, characterized in that In step 7), the drying is carried out by hot air drying method, and the drying conditions are: temperature of 35-55° C., wind speed of 2-3 m / s, drying time of 18-24 h, and after drying, the mixture is crushed and passed through a 100-mesh sieve.

9. A low glycemic index starch prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the low glycemic index starch as claimed in claim 9 in preparing food for diabetic patients.

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