Preparation method of high-substitution-degree V-type pre-gelatinized hydroxypropyl starch

Abstract

The invention discloses a preparation method of high-substitution-degree V-type pre-gelatinized hydroxypropyl starch, and belongs to the technical field of starch modification. The preparation method comprises the following steps: (1) extruding starch and an ethanol water solution, drying and crushing to obtain extruded modified starch A; and (2) adding the extruded modified starch A into an ethanol solution, adjusting the pH value to be alkaline, adding epoxypropane for reaction, adjusting the pH value to be acidic, terminating the reaction, and then performing suction filtration, washing and drying to finally obtain the V-type pre-gelatinized hydroxypropyl starch. The preparation method comprises the following steps: firstly, carrying out alcohol-water extrusion treatment to obtain V-shaped pre-gelatinized starch which has a V-shaped single-spiral structure, has a large amount of exposed hydroxyl groups and is relatively high in reaction activity; and subsequently, an organic solvent method is adopted to carry out hydroxypropylation reaction, so that the reaction efficiency is improved, the product efficiency is improved, and the cost is reduced.

Description

Technical Field

[0001] The invention relates to a method for preparing high-substitution degree V-type pregelatinized hydroxypropyl starch, belonging to the technical field of starch modification. Background Art

[0002] Hydroxypropyl starch is a starch substituted ether obtained by introducing hydroxypropyl groups into starch molecules through the reaction of propylene oxide with hydroxyl groups in an alkaline environment. Since the hydroxypropyl group has strong hydrophilicity, it can weaken the hydrogen bond strength inside the starch molecule and increase the hydrogen bond strength between the starch molecule and the water molecule. Therefore, this modification process can significantly improve the transparency, stability and anti-retrogradation of starch paste, making it have excellent performance in different application fields.

[0003] Hydroxypropyl pregelatinized starch is a functional starch obtained by dual modification of pregelatinization and hydroxypropylation. Hydroxypropyl pregelatinized starch has excellent solubility in water, especially in cold water, where its dissolution rate is much higher than that of ordinary starch, making it easy to process and use. Since the pregelatinization process allows the starch to retain part of its gelatinized structure after drying, hydroxypropylation further improves its thermal stability and anti-retrogradation properties, making this type of starch exhibit strong stability and reducing aging. Therefore, hydroxypropyl pregelatinized starch is widely used in the fields of ready-to-eat foods, beverages, and pharmaceuticals, and has important application value, especially in products that require rapid dissolution, thickening, and gelling.

[0004] The preparation of hydroxypropyl pregelatinized starch is to first perform hydroxypropylation and then pregelatinization, but because the ungelatinized starch granule structure is relatively dense, the hydroxypropylation reaction efficiency is low, and it is easy to have incomplete reaction or side reactions, which affects the quality of the final product. In addition, after hydroxypropylation, the molecular structure of starch has undergone certain changes. If pregelatinization is performed again, the gel properties and thickening performance of starch may decrease. Therefore, the preparation method of the above-mentioned traditional hydroxypropyl pregelatinized starch has certain disadvantages. The process of pregelatinization first and then hydroxypropylation can effectively avoid the problems in the traditional preparation method to improve the overall performance of starch, but the hydroxypropyl pregelatinized starch finally obtained still has the problems of low degree of substitution and high agglomeration rate.

[0005] The problem of low degree of substitution is usually optimized by adjusting the amount of propylene oxide, increasing the pH value of the reaction, and increasing the reaction temperature. Among them, increasing the amount of propylene oxide is the most effective. By increasing the concentration of epoxy groups in starch, it increases the probability of reaction with swollen starch free radicals, thereby increasing the degree of etherification. However, according to the requirements of GB 29930-2013, the mass fraction of hydroxypropyl in food additive hydroxypropyl starch shall not exceed 7%. Therefore, in the field of food additives, the amount of propylene oxide added should not be higher than 7%, which limits the increase in the degree of substitution of hydroxypropyl pregelatinized starch.

[0006] Recent studies have found that V-type starch modified by alcohol-water extrusion has stronger reactivity than native starch. This is because the hydrophobic hydroxyl groups of the V-type single helix are exposed, which allows propylene oxide to have more attacking sites during the reaction. Therefore, the use of V-type starch modified by alcohol-water extrusion to prepare hydroxypropyl pregelatinized starch is expected to achieve higher reaction efficiency and thus increase the degree of substitution of hydroxypropyl pregelatinized starch.

[0007] At present, there is no technical report on the use of alcohol-water extrusion-modified V-starch for hydroxypropylation in the prior art. At the same time, the present invention finds that not all alcohol-water extrusion-modified V-starches can successfully increase the degree of substitution of the obtained hydroxypropyl pregelatinized starch. In addition, the patents CN 118206669 A, CN 116284462 A, CN112831081 A, and CN 115975059 A all disclose methods for preparing V-starch by alcohol-water extrusion, but none of them disclose that the obtained V-starch can successfully prepare a hydroxypropyl pregelatinized starch with a high degree of substitution. Therefore, it is necessary to explore under what conditions the alcohol-water extrusion-modified V-starch can successfully increase the degree of substitution of hydroxypropyl pregelatinized starch. Summary of the invention

[0008] Technical issues

[0009] The existing pregelatinized hydroxypropyl starch preparation generally has the problems of low substitution efficiency and complicated preparation process. Therefore, it is necessary to provide a simple and efficient method for preparing pregelatinized hydroxypropyl starch, so that the obtained product has a high degree of substitution while reducing the production cost. The preparation of hydroxypropyl pregelatinized starch using V-type starch modified by alcohol-water extrusion is a promising approach, but it is necessary to explore under what conditions the V-type starch can successfully improve the degree of substitution of hydroxypropyl pregelatinized starch.

[0010] Technical Solution

[0011] The present invention proposes an innovative process flow, that is, firstly, V-type pregelatinized starch is prepared by alcohol-water extrusion, and then hydroxypropylated. Different from the traditional process of first hydroxypropylation and then gelatinization, the process of the present invention effectively overcomes some limitations of the conventional method, and it is additionally found that the V-type pregelatinized hydroxypropyl starch prepared by the process of the present invention has better dispersibility and lower agglomeration rate in cold water compared with the traditional pregelatinized hydroxypropyl starch, which has certain reference significance for the research and development of instant instant powder. At the same time, the quality of the pregelatinized starch product is better, the extrusion method has a larger output, lower cost, and has great market prospects.

[0012] The object of the present invention is to provide a method for preparing V-type pregelatinized hydroxypropyl starch, comprising the following steps:

[0013] (1) firstly extruding starch and ethanol aqueous solution and then drying and crushing them to obtain extruded modified starch A;

[0014] (2) adding the extruded modified starch A to an ethanol solution, adjusting the pH to alkaline, adding propylene oxide to react, adjusting the pH to acidic to terminate the reaction, then filtering, washing, and drying to finally obtain V-type pregelatinized hydroxypropyl starch.

[0015] In one implementation method of the present invention, the starch includes one or more of ordinary corn starch, rice starch, potato starch, wheat starch, barley starch, and tapioca starch.

[0016] In one implementation method of the present invention, the concentration of ethanol in the ethanol aqueous solution in step (1) is 30-50%, v / v.

[0017] In one implementation method of the present invention, the mass ratio of starch to ethanol aqueous solution in step (1) is 1:0.4 to 1:1.

[0018] In one embodiment of the present invention, the extrusion in step (1) is performed using an extruder.

[0019] In one implementation method of the present invention, the parameters of the extruder are set as follows: the heating temperature of the premixing zone is 50-60°C, the temperature of the gelatinization zone is 70-100°C, the temperature of the molding zone is 40-50°C, and the extruder speed is 80-200r / min.

[0020] In one implementation method of the present invention, the pulverization in step (1) can be performed using a continuous cyclone pulverizer, wherein the screen size is 0.8 to 1.5 mm.

[0021] In one implementation method of the present invention, the concentration of ethanol in the ethanol solution in step (2) is 80-100%, v / v.

[0022] In one implementation method of the present invention, the mass ratio of the extruded modified starch A to the ethanol solution in step (2) is 1:3 to 1:4.

[0023] In one implementation method of the present invention, the step (2) of adjusting the pH to alkaline is adjusting the pH value to 10.5-12.0.

[0024] Preferably, the step of adjusting the pH to alkaline is adjusting the pH value to 11.0-11.5.

[0025] In one implementation method of the present invention, the amount of propylene oxide added in step (2) is 5-7% of the mass of the starch.

[0026] Specifically, optionally, the amount of propylene oxide added in step (2) is 7% of the mass of the starch.

[0027] In one embodiment of the present invention, the reaction process of step (2) is to add propylene oxide and maintain the temperature at 60 to 80° C. for 4 to 10 hours.

[0028] In one implementation method of the present invention, the step (2) of adjusting the pH to acidic is to adjust the pH value of the system to 4.0-6.0.

[0029] In one embodiment of the present invention, washing is performed using anhydrous ethanol or an ethanol aqueous solution.

[0030] In one embodiment of the present invention, the drying temperature in step (2) is 40-60°C.

[0031] The present invention provides V-type pregelatinized hydroxypropyl starch prepared according to the method.

[0032] The V-type pregelatinized hydroxypropyl starch prepared by the invention is applied in the food field.

[0033] Furthermore, the application includes preparing instant mixing powder, seasoning sauce, soluble capsule or edible film.

[0034] Beneficial Effects

[0035] (1) Excellent product performance: The present invention obtains a V-type pregelatinized starch with high reactivity and a V-shaped single helical crystal structure by first using an alcohol-water extrusion method. The V-type pregelatinized starch can achieve an increase in the degree of substitution in the subsequent hydroxypropylation, and the degree of substitution of the obtained hydroxypropyl starch is increased to above 0.9. At the same time, it also has a good water separation rate and a low agglomeration rate.

[0036] (2) Efficient and simple preparation: The preparation process of the present invention is simple, with few steps and large output, and is suitable for industrial application. In addition, a high degree of substitution hydroxypropyl starch prepared when the amount of propylene oxide added does not exceed 7% meets the national standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 X-ray diffraction patterns of V-type pregelatinized starch, V-type pregelatinized hydroxypropyl starch, and native starch prepared in Example 1 of the present invention and corresponding relative crystallinity diagram DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0039] 1. Test method for freeze-thaw stability:

[0040] Weigh a certain amount of sample, place it in a pre-weighed centrifuge tube M0, prepare a 3% (dry basis) starch paste, record the total weight M1, and cool to room temperature. Place it in a refrigerator at -18°C for 24 hours, take it out, thaw it naturally at room temperature for 2 hours, then centrifuge it at 3000r / min for 20 minutes, remove the supernatant and weigh M2, and calculate the water separation rate. The formula is as follows:

[0041] Water separation rate % = [(M1-M2) / (M1-M0)] × 100%

[0042] The cycle was repeated five times and the fifth water extraction rate was taken as the final data.

[0043] 2. Crystallinity test method:

[0044] The crystal structure of the sample was analyzed by X-ray diffractometer, with a scanning angle of 3-36° (2θ) and a scanning speed of 0.05° / s. The relative crystallinity was calculated by MDI JADE software: the ratio of the area of ​​the characteristic peaks of type V crystals (7.8°, 13.5° and 20.8°) or the area of ​​the characteristic peaks of type A crystals (15°, 17°, 18° and 23°) to the total dispersion area. The calculation formula is as follows:

[0045] Relative crystallinity (%) = CDA / TDA × 100

[0046] Where CDA represents the peak area of ​​the characteristic crystalline peak, and TDA represents the total area of ​​all diffraction peaks in the scanning interval.

[0047] 3. Test method for degree of substitution:

[0048] Accurately weigh 0.04-0.06g of oxidized hydroxypropyl starch sample and transfer it to a 100mL volumetric flask. Use a pipette to measure 25mL of 0.5mol / L sulfuric acid solution and add it to the volumetric flask. Heat it in a boiling water bath to fully gelatinize the starch. After heating for 30 minutes, cool the starch paste solution in the volumetric flask to room temperature. Prepare a 25mL stoppered glass test tube in advance, soak it in an ice water bath, take 1mL of the above starch paste solution and add it to the stoppered glass test tube, then carefully and slowly continue to add 8mL of concentrated sulfuric acid, and mix the glass test tube upside down. Heat the glass test tube in a boiling water bath for 30 minutes, and immediately put the glass test tube in an ice water bath after the reaction is completed. After the sample cools to room temperature, slowly add 0.6mL of 3% ninhydrin indicator solution, shake it upside down, let it stand in a 25℃ water bath for 100 minutes, then add concentrated sulfuric acid to make the liquid volume in the test tube reach 25mL, and shake it upside down. Using distilled water as a comparison, transfer to a cuvette and let stand for 5 minutes. Use an ultraviolet spectrophotometer to measure the absorbance at 595nm, and calculate the hydroxypropyl molar substitution of the sample based on the converted propylene glycol content. The mass fraction of hydroxypropyl (H)%, the molar substitution (MS) of hydroxypropyl starch is calculated according to the following formula:

[0049] H(%)=F[M1 / W1-M0 / W0]×0.7763×100

[0050] MS=2.79H / (100-H)

[0051] in:

[0052] H—percentage of hydroxypropyl, %;

[0053] F—dilution multiple of sample or blank;

[0054] M1—the mass of propylene glycol in the sample found on the standard working curve, g;

[0055] M0—the mass of propylene glycol in the native starch blank sample found on the standard working curve, g;

[0056] W1—sample mass, g;

[0057] W0—original starch mass, g;

[0058] 0.7763—Conversion coefficient of propylene glycol content to hydroxypropyl content;

[0059] 2.79—Conversion factor for converting hydroxypropyl percentage to degree of substitution.

[0060] 4. Test method for agglomeration rate:

[0061] Measure 100mL of deionized water and heat it to boiling on an induction cooker. Weigh 5g of sample and place it in a beaker. Measure 30mL of deionized water cooled to 80°C and add it to the beaker. Stir it thoroughly with a glass rod for 5 minutes, then let it stand for 1 minute to observe whether there is stratification. Take a 20-mesh sieve (record the weight), filter the sample solution, slowly rinse the lumps with clean water, put it in a 105°C oven and dry it to constant weight before weighing. Subtract the weight of the sieve to get the dry matter weight of the lumps. The lumping rate is calculated according to formula (2-1).

[0062]

[0063] Where m is the dry weight of the agglomerate (g), M is the sample mass (g), and a is the moisture content of the sample (%).

[0064] Example 1

[0065] Select cassava starch, set the solid feed rate of the extruder to 600g / h; prepare an ethanol aqueous solution with an ethanol volume concentration of 40% and set the liquid feed rate so that the mass ratio of starch to ethanol aqueous solution is 1:0.56. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60°C, the temperature of the gelatinization zone is 95°C, the temperature of the molding zone is 50°C, and the speed of the extruder is 100r / min. The extrudate is cut into 0.5cm small segments and placed in an oven at 40°C for drying for 20h. Then it is taken out and placed in a continuous cyclone mill (screen size is 1.0mm) for pulverization to obtain V-type pregelatinized starch A.

[0066] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 30 mL of 85% ethanol aqueous solution was added, the pH was adjusted to 11.0 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 75°C for 6 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After filtration, washing, drying and crushing, pregelatinized hydroxypropyl starch was obtained.

[0067] Example 2

[0068] Potato starch was selected, and the solid feed rate of the extruder was set to 600 g / h; an ethanol aqueous solution with an ethanol volume concentration of 35% was prepared and the mass ratio of starch to ethanol aqueous solution was set to 1:0.48 by setting the liquid feed rate. The operating parameters of the extruder were: the heating temperature of the premixing zone was 60°C, the temperature of the gelatinization zone was 100°C, the temperature of the molding zone was 50°C, and the speed of the extruder was 100 r / min. The extrudate was cut into 0.5 cm small segments and placed in an oven at 40°C for drying for 24 hours. It was then taken out and placed in a continuous cyclone mill (screen size was 1.0 mm) for pulverization to obtain V-type pregelatinized starch A.

[0069] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 30 mL of 90% ethanol aqueous solution was added, the pH was adjusted to 11.6 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 80°C for 8 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After filtration, washing, drying and crushing, hydroxypropyl starch was obtained.

[0070] Example 3

[0071] Select barley starch, set the solid feed rate of the extruder to 600g / h; prepare an ethanol aqueous solution with an ethanol volume concentration of 40% and set the liquid feed rate so that the mass ratio of starch to ethanol aqueous solution is 1:0.56. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60°C, the temperature of the gelatinization zone is 95°C, the temperature of the molding zone is 50°C, and the extruder speed is 140r / min. The extrudate is cut into 0.5cm small segments and placed in an oven at 40°C for drying for 20h. Then it is taken out and placed in a continuous cyclone mill (screen size is 1.0mm) for pulverization to obtain V-type pregelatinized starch A.

[0072] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 30 mL of 95% ethanol aqueous solution was added, the pH was adjusted to 11.7 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 65°C for 6 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After suction filtration, washing, drying and crushing, hydroxypropyl starch was obtained.

[0073] Example 4

[0074] Ordinary corn starch was selected, and the solid feed rate of the extruder was set to 600g / h; an ethanol aqueous solution with a volume concentration of 40% was prepared and the mass ratio of starch to ethanol aqueous solution was set to 1:0.4 by setting the liquid feed rate. The operating parameters of the extruder were: the heating temperature of the premixing zone was 60°C, the temperature of the gelatinization zone was 90°C, the temperature of the molding zone was 50°C, and the speed of the extruder was 120r / min. The extrudate was cut into 0.5cm small segments and placed in an oven at 40°C for drying for 20h. It was then taken out and placed in a continuous cyclone mill (screen size was 1.0mm) for pulverization to obtain V-type pregelatinized starch A.

[0075] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 30 mL of anhydrous ethanol was added, the pH was adjusted to 11.3 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 60°C for 4 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After suction filtration, washing, drying and crushing, hydroxypropyl starch was obtained.

[0076] Example 5

[0077] Select wheat starch, set the solid feed rate of the extruder to 600g / h; prepare ethanol solution with a volume concentration of 40% ethanol and set the liquid feed rate so that the mass ratio of starch to ethanol solution is 1:0.7. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60°C, the temperature of the gelatinization zone is 80°C, the temperature of the molding zone is 50°C, and the speed of the extruder is 160r / min. Cut the extrudate into 0.5cm small segments and place it in an oven at 40°C for drying for 24h. Then take it out and place it in a continuous cyclone mill (screen size is 1.0mm) for crushing to obtain V-type pregelatinized starch A.

[0078] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 35 mL of anhydrous ethanol was added, the pH was adjusted to 11.1 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The mixture was reacted in a water bath at 75°C for 4 h, and finally, the pH value was adjusted to 4.5 with 10% hydrochloric acid solution to terminate the reaction. Hydroxypropyl starch was obtained after filtration, washing, drying and crushing.

[0079] Example 6

[0080] Select rice starch, set the solid feed rate of the extruder to 600g / h; prepare an ethanol solution with a volume concentration of 40% ethanol and set the liquid feed rate so that the mass ratio of starch to ethanol solution is 1:0.9. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60°C, the temperature of the gelatinization zone is 75°C, the temperature of the molding zone is 50°C, and the speed of the extruder is 160r / min. The extrudate is cut into 0.5cm small segments and placed in an oven at 40°C for drying for 20h. Then it is taken out and placed in a continuous cyclone mill (screen size is 1.0mm) for pulverization to obtain V-type pregelatinized starch A.

[0081] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 40 mL of anhydrous ethanol was added, the pH was adjusted to 11.0 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 65°C for 8 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After suction filtration, washing, drying and crushing, hydroxypropyl starch was obtained.

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is that in step (1), ethanol is not added, but deionized water is used for extrusion. The specific steps are as follows:

[0084] Select cassava starch, set the solid feed rate of the extruder to 600g / h; take deionized water and set the liquid feed rate so that the mass ratio of starch to deionized water is 1:0.56. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60℃, the temperature of the gelatinization zone is 95℃, the temperature of the molding zone is 50℃, and the extruder speed is 100r / min. Cut the extrudate into 0.5cm small segments and place it in an oven at 40℃ for 20h. Then take it out and place it in a continuous cyclone mill (screen size is 1.0mm) for crushing to obtain alcohol-free extruded pregelatinized starch.

[0085] Subsequently, 10 g of alcohol-free extruded pregelatinized starch was weighed and placed in a 50 mL centrifuge tube, 30 mL of 85% ethanol aqueous solution was added, the pH was adjusted to 11.0 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 75°C for 6 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After suction filtration, washing, drying and crushing, pregelatinized hydroxypropyl starch was obtained.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that step (1) is not performed, and the hydroxypropyl substitution reaction is directly performed on the native starch; the specific steps are as follows:

[0088] Weigh 10g of cassava starch, place it in a 50mL centrifuge tube, add 30mL of 85% ethanol aqueous solution, adjust the pH to 11.0 with 10% sodium hydroxide solution, then add 0.7g of propylene oxide, react in a water bath at 75°C for 6h, finally use 10% hydrochloric acid solution to adjust the pH to 5.0 to terminate the reaction, filter, wash, dry and crush to obtain hydroxypropyl starch.

[0089] Comparative Example 3

[0090] Select cassava starch, set the solid feed rate of the extruder to 600g / h; prepare an ethanol aqueous solution with an ethanol volume concentration of 40% and set the liquid feed rate so that the mass ratio of starch to ethanol aqueous solution is 1:1.5. The operating parameters of the extruder are: the heating temperature of the premixing zone is 60°C, the temperature of the gelatinization zone is 95°C, the temperature of the molding zone is 50°C, and the extruder speed is 100r / min. The extrudate is cut into 0.5cm small segments and placed in an oven at 40°C for drying for 20h. Then it is taken out and placed in a continuous cyclone mill (screen size is 1.0mm) for pulverization to obtain V-type pregelatinized starch A.

[0091] Subsequently, 10 g of V-type pregelatinized starch A was weighed and placed in a 50 mL centrifuge tube, 30 mL of 85% ethanol aqueous solution was added, the pH was adjusted to 11.0 with 10% sodium hydroxide solution, and 0.7 g of propylene oxide was added. The reaction was carried out in a water bath at 75°C for 6 hours, and finally, the pH value was adjusted to 5.0 with 10% hydrochloric acid solution to terminate the reaction. After filtration, washing, drying and crushing, pregelatinized hydroxypropyl starch was obtained.

[0092] The hydroxypropyl starch prepared in Examples 1 to 6 and Comparative Examples 1 to 2 was tested for degree of substitution and water separation rate. The specific results are shown in Table 1 below:

[0093] Table 1 Examples 1 to 6 and Comparative Examples 1 to 2

[0094]

[0095] As can be seen from Table 1, the degree of substitution of the hydroxypropyl starch prepared in the embodiment of the present invention is greater than 0.09, as high as 0.157, when only 7% of propylene oxide is added, and is significantly higher than the hydroxypropyl starch prepared in Comparative Examples 1 to 2. It can be seen that the V-type starch after alcohol-water extrusion has a high reaction activity and can be used to efficiently prepare hydroxypropyl pregelatinized starch. However, since the hydroxypropyl group itself is relatively large, there is a certain steric hindrance between the sugar chains and the hydroxypropyl group enhances the hydrogen bonds between the starch molecules and the water molecules in the water system, which makes the starch easier to disperse and dissolve.

[0096] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing V-type pregelatinized hydroxypropyl starch, characterized in that: The following steps are involved: (1) firstly extruding starch and ethanol aqueous solution and then drying and crushing them to obtain extruded modified starch A; the concentration of ethanol in the ethanol aqueous solution is 30 to 50%, v / v; and the mass ratio of starch to ethanol aqueous solution is 1:0.4 to 1:1; (2) adding the extruded modified starch A to an ethanol solution, adjusting the pH to alkaline, adding propylene oxide to react, adjusting the pH to acidic to terminate the reaction, then filtering, washing, and drying to finally obtain V-type pregelatinized hydroxypropyl starch.

2. The method according to claim 1, characterized in that The starch includes one or more of ordinary corn starch, rice starch, potato starch, wheat starch, barley starch, and tapioca starch.

3. The method according to claim 1, characterized in that In step (1), extrusion is performed by using an extruder; the parameters of the extruder are set as follows: the heating temperature of the premixing zone is 50-60°C, the temperature of the gelatinization zone is 70-100°C, the temperature of the molding zone is 40-50°C, and the extruder speed is 80-200r / min.

4. The method according to claim 1, characterized in that The concentration of ethanol in the ethanol solution in step (2) is 80-100%, v / v.

5. The method according to claim 1, characterized in that The mass ratio of the extruded modified starch A to the ethanol solution in step (2) is 1:3 to 1:

4.

6. The method according to claim 1, characterized in that The step (2) of adjusting the pH to alkaline is to adjust the pH value to 10.5-12.

0.

7. The method according to claim 1, characterized in that The amount of propylene oxide added in step (2) is 5-7% of the mass of the starch; the reaction process in step (2) is to maintain the temperature at 60-80° C. for 4-10 hours after adding propylene oxide.

8. The method according to claim 1, characterized in that The step (2) of adjusting the pH to acidity is to adjust the pH value of the system to 4.0-6.

0.

9. A V-type pregelatinized hydroxypropyl starch, characterized in that: The V-type pregelatinized hydroxypropyl starch is prepared according to the method according to any one of claims 1 to 8.

10. Use of the V-type pregelatinized hydroxypropyl starch according to claim 9 in the food field.

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