Resistant starch and preparation method thereof

Abstract

The invention belongs to the technical field of food processing, and particularly relates to resistant starch and a preparation method thereof. The preparation method mainly comprises the following steps: soaking, grinding, deproteinization, gelatinization, acidolysis, debranching, heating, retrogradation and purification. The preparation method disclosed by the invention is innovated and improved on the basis of an original traditional preparation method, a microwave-infrared heating method is introduced, a physical method, a chemical method and an enzyme method are combined, and the prepared red date resistant starch has the characteristics of high resistant content, low impurity content, uniform color, high quality and good heat resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a resistant starch and a preparation method thereof. Background Art

[0002] Resistant starch (RS) refers to a type of starch that cannot be digested and absorbed in the stomach and small intestine, but can be fermented and decomposed by intestinal bacteria in the human colon to produce short-chain fatty acids and play a probiotic role, also known as anti-enzyme-digested starch. According to the properties of RS, the classification of RS covers five types: RS1 (physically embedded starch), RS2 (resistant starch granules), RS3 (retrograded starch), RS4 (chemically modified starch), and RS5 (starch-lipid complex). After heat treatment, the structures of RS1 and RS2 are easily damaged, so their anti-enzyme-digested properties are weak. RS3 is formed by the amylose in starch molecules during the processes of retrogradation and recrystallization, such as the cooling process of gelatinized starch, so it has extremely high stability in a hot environment. RS4 is a type of starch whose molecular structure has changed through esterification, etherification, or cross-linking, and its safety remains to be verified. The formation of RS5 results from the complexation between amylose and lipids, but the production cost is high after introducing lipids, and the yield is unstable.

[0003] Among them, RS3 resistant starch has broad application prospects due to its safety and high efficiency. It can improve intestinal health, promote the growth of beneficial bacteria, enhance intestinal peristalsis, and prevent constipation and intestinal diseases. It can also help control blood sugar, slow down the rising speed of postprandial blood sugar, and is beneficial to diabetic patients. At the same time, it increases satiety and helps control appetite and weight. In addition, RS3 resistant starch also has a certain lipid-lowering effect, which can reduce the cholesterol level in the blood, thereby reducing the risk of cardiovascular diseases.

[0004] Jujube is a widely planted crop in China. At present, the processed products of jujube are mainly primary processed, such as jujube powder, dried jujube, etc. With the growth of market demand and the progress of technology, the processing and utilization level of jujube is expected to be further improved. At present, the types of commercially available resistant starch products in the Chinese market are limited, while jujube contains a high starch content. About 80 grams of starch are contained in 100 grams of jujube, so it is a good raw material for preparing resistant starch.

[0005] In order to solve the problems existing in the extraction of resistant starch, such as "few varieties, low purity, and poor heat resistance", the technical solution of the present invention is proposed. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention uses red dates as raw materials, introduces the microwave-infrared heating method, and provides a preparation process combining physical, chemical, and enzymatic methods to improve the purity of resistant starch without changing the nature and structure of starch, broaden the variety of domestic resistant starch, and improve the heat resistance of resistant starch. The solution of the present invention is to provide a method for preparing resistant starch, and the preparation method includes the following steps: (1) Soaking: After removing the pits from fresh red dates, soak them in water, wash them with water, and remove impurities to obtain clean red dates; (2) Pulping: Cut the clean red dates into small pieces, add water for pulping, and collect and obtain the first slurry; (3) Sugar removal: Add yeast to the first slurry, introduce air and continuously stir to remove the sugar in the first slurry, and the slurry after sugar removal is the second slurry; (4) Protein removal: Adjust the pH of the second slurry to neutral, add neutral protease to remove proteins, and then centrifuge the slurry to obtain a precipitate; Wash, dry, crush, and sieve the precipitate in sequence to obtain red date starch; (5) Gelatinization: Add the red date starch to water and gelatinize it under ultrasonic and high-temperature and high-pressure conditions; (6) Acid hydrolysis: Then add hydrochloric acid-acetic acid solution to adjust the pH to acidic, and then add potassium hydrogen phthalate-sodium hydroxide buffer solution, and fully stir to obtain gelatinized acid-hydrolyzed starch milk; (7) Debranching: Add alkali solution, pullulanase, and medium-temperature α-amylase to the gelatinized acid-hydrolyzed starch milk for debranching, and inactivate the enzyme after completion to obtain debranched starch milk; (8) Heating up and retrogradation: Carry out microwave-infrared heating treatment on the debranched starch milk, and then let it stand for aging and retrogradation to obtain retrograded starch milk; (9) Purification: Add glucosidase to the retrograded starch milk to enzymatically hydrolyze non-resistant starch, then centrifuge and discard the supernatant, and wash, dry, and sieve the precipitate in sequence to obtain red date resistant starch.

[0007] Preferably, in step (1), the soaking time is 4 to 24 h.

[0008] Preferably, in step (2), the mass of the added water is 5 to 10 times the mass of the clean red dates.

[0009] Preferably, in step (3), the addition amount of the yeast is 2% to 5% of the mass of the red dates.

[0010] Preferably, in step (4), the addition amount of the neutral protease is 200 to 1200 U / g; And / or, after adding neutral protease, during the process of removing protein, keep the temperature of the slurry at 37 - 50 °C; And / or, the rotation speed of the centrifugation is 3000 - 3500 r / min, and the centrifugation time is 15 - 20 min; And / or, the drying temperature is 50 - 55 °C; And / or, the sieving is through a 100 - 120 mesh sieve.

[0011] Preferably, in step (5), add the red date starch into water and keep the concentration of the red date starch at 10 - 35 wt%; And / or, the conditions of ultrasonic and high temperature and high pressure are: the ultrasonic power is 80 - 240 W, the high temperature is 121 °C, and the high pressure is 1.0 - 1.2 MPa; And / or, the gelatinization time is 15 - 90 min.

[0012] Preferably, in step (6), the concentration of the hydrochloric acid - acetic acid solution is 25 - 75 wt%; And / or, add the hydrochloric acid - acetic acid solution to adjust the pH to 3 - 5, and keep the pH less than 5 during the acid hydrolysis process.

[0013] Preferably, in step (7), the alkali solution is a mixed solution of 1 wt% NaOH solution and 0.5 wt% KOH solution; And / or, the addition amount of pullulanase is 50 - 300 U / g; And / or, the addition amount of medium - temperature α - amylase is 10 - 35 U / g; And / or, the de - branching temperature is 50 - 60 °C, and the de - branching time is 4 h.

[0014] Preferably, in step (8), the heating power of the microwave is 300 - 900 W; And / or, the wavelength of the infrared heating is 2 - 10 μm, and the infrared heating power is 200 - 1200 W; And / or, the microwave - infrared heating time is 2 - 12 min; And / or, the temperature of aging and retrogradation is 4 °C, and the time is 18 - 48 h.

[0015] Preferably, in step (9), the addition amount of glucosidase is 50 - 300 U / g; And / or, the rotation speed of the centrifugation is 3000 - 3500 r / min, and the centrifugation time is 15 - 20 min; And / or, the drying temperature is 60 - 65 °C; And / or, the sieving is through a 100 - 120 mesh sieve.

[0016] Based on the same inventive concept, another solution of the present invention is to provide a resistant starch obtained by the preparation method.

[0017] The beneficial effects of the present invention are as follows: (1) For the preparation method of the present invention, the advantage of using hydrochloric acid combined with acetic acid hydrolysis in the preparation of jujube resistant starch is that it can enhance the acid hydrolysis effect, improve the yield and purity of resistant starch through synergistic effects, and at the same time reduce the usage amount and potential side effects of a single acid to a certain extent.

[0018] (2) For the preparation method of the present invention, the advantage of using microwave-infrared heating method in the preparation of jujube resistant starch is that it is energy-efficient and can accurately control the heating temperature, enabling starch molecules to reach the reaction conditions in a shorter time, reducing heat loss, and improving the preparation efficiency and product quality.

[0019] (3) For the preparation method of the present invention, the advantage of using glucosidase in the preparation of jujube resistant starch is that it can specifically act on starch molecules, efficiently remove impurities, improve the purity and quality of resistant starch, and at the same time maintain its natural structure and health value.

[0020] (4) The jujube resistant starch prepared by the preparation method of the present invention has the characteristics of high resistant content, low impurity content, uniform color, excellent quality, and good heat resistance, and can be used in the food industry. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 is the process flow chart of the present invention.

[0023] Figure 2 is the structural schematic diagram of the microwave-infrared heating device.

[0024] Figure 3 is the scanning electron microscope image of jujube starch before treatment under different magnifications (from left to right: ×500, ×1000, ×5000).

[0025] Figure 4 is the scanning electron microscope image of the jujube resistant starch obtained in Example 6 under different magnifications (from left to right: ×500, ×1000, ×5000).

[0026] Figure 5 These are the XRD patterns of red date starch and red date resistant starch.

[0027] Figure 6 These are the FTIR patterns of red date starch and red date resistant starch.

[0028] Figure 7 These are the DSC patterns of red date starch and red date resistant starch.

[0029] Figure 8 These are the swelling degrees of red date starch and red date resistant starch at different temperatures.

[0030] Reference numerals in the figures: 1 - magnetic stirrer; 2 - infrared heater; 3 - starch container; 4 - microwave heater. Detailed implementation manners

[0031] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other implementation manners obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope protected by the present invention.

[0032] Embodiment 1 This embodiment provides a method for preparing resistant starch, and the preparation method includes the following steps: (1) Soaking: After removing the pits from fresh red dates, soak them in water for 4 h, wash them with water, and remove impurities to obtain clean red dates; (2) Pulping: Cut the clean red dates into small pieces, add 5 times the amount of water, and perform pulping 3 times, and collect and obtain the first slurry; (3) Sugar removal: Add yeast accounting for 2% of the mass of the red dates to the first slurry, introduce air and continuously stir to remove the sugar in the first slurry, and the slurry after sugar removal is the second slurry; (4) Protein removal: Adjust the pH of the second slurry to neutral, add neutral protease at 200 U / g to remove proteins (keep the temperature at 37 °C), then centrifuge the slurry at 3000 r / min for 20 min to obtain a precipitate; Wash the precipitate 3 times with distilled water, then dry it in an oven at 50 °C, pulverize it, and pass it through a 100-mesh sieve to obtain red date starch; (5) Gelatinization: Add the red date starch to water, control the concentration to be 10 wt%, and fully gelatinize it at 80 W power and 121 °C in an ultrasonic autoclave for 15 min; (6) Acid hydrolysis: Then, add a 25 wt% hydrochloric acid - acetic acid solution to adjust the pH to 5.0, and then add a potassium hydrogen phthalate - sodium hydroxide buffer solution. After sufficient stirring, a gelatinized and acid-hydrolyzed starch milk is obtained; (7) Debranching: Place the gelatinized and acid-hydrolyzed starch milk in a 50 °C constant temperature water bath, and add a mixed solution of 1 wt% NaOH solution and 0.5 wt% KOH solution to adjust the pH to 6.0. Then, add 50 U / g of pullulanase and 10 U / g of medium-temperature α-amylase for sufficient debranching for 4 h. After completion, inactivate the enzyme in a boiling water bath to obtain debranched starch milk; (8) Heating and retrogradation: Heat the debranched starch milk at a microwave power of 300 W and an infrared heating power of 200 W for 2 min while stirring; then let it stand at 4 °C for 18 h for aging and retrogradation to obtain retrograded starch milk; (9) Purification: Add 50 U / g of glucosidase to the retrograded starch milk to enzymatically hydrolyze non-resistant starch, then centrifuge at 3000 r / min for 20 min and discard the supernatant. Wash the precipitate 3 times with absolute ethanol, place it in a 60 °C oven for drying, and pass it through a 100-mesh sieve to obtain red date resistant starch (seal and store in a desiccator).

[0033] The process flow chart is as Figure 1 shown.

[0034] It should be emphasized that in step (8), a microwave - infrared heating device is required, and its structural schematic diagram is as Figure 2 shown.

[0035] Example 2 This example provides a method for preparing resistant starch, and the preparation method includes the following steps: (1) Soaking: After removing the pits from fresh red dates, soak them in water for 8 h, wash them with water, and remove impurities to obtain clean red dates; (2) Pulping: Cut the clean red dates into small pieces, add 10 times the amount of water, and pulp them 3 times. Collect and obtain the first slurry; (3) Sugar removal: Add 5% of the mass of yeast in red dates to the first slurry, introduce air and continuously stir to remove the sugar in the first slurry. The slurry after sugar removal is the second slurry; (4) Protein removal: Adjust the pH of the second slurry to neutral, and add 400 U / g of neutral protease to remove proteins (keep the temperature at 37 °C). Then, centrifuge the slurry at 3500 r / min for 15 min to obtain a precipitate; Wash the precipitate 3 times with distilled water, then dry it in a 50 °C oven, crush it, and pass it through a 120-mesh sieve to obtain red date starch; (5) Gelatinization: the red date starch was added into water to control the concentration to 15 wt %, and fully gelatinized in an ultrasonic pressure cooker at 240 W power and 121 ° C for 30 min; (6) Acid hydrolysis: then add a 25 wt% hydrochloric acid-acetic acid solution to adjust the pH to 5.0, then add a potassium hydrogen phthalate-sodium hydroxide buffer solution, and stir thoroughly to obtain a gelatinized acid-hydrolyzed starch emulsion; (7) Debranching: placing the gelatinized acid-hydrolyzed starch milk in a constant temperature water bath at 50° C., adding a mixture of 1 wt % NaOH solution and 0.5 wt % KOH solution to adjust the pH to 6.0, then adding 100 U / g pullulanase and 15 U / g mesophilic α-amylase to fully debranch for 4 h, and after completion, inactivating the enzymes in a boiling water bath to obtain debranched starch milk; (8) Heating and retrograding: heating the debranched starch emulsion at a microwave power of 300 W and an infrared heating power of 400 W for 4 min while stirring; then standing at 4° C. for 24 h for aging and retrogradation to obtain retrograded starch emulsion; (9) Purification: 100 U / g of glucosidase was added to the retrograded starch milk to enzymatically hydrolyze the non-resistant starch, and then the mixture was centrifuged at 3500 r / min for 15 min and the supernatant was discarded. The precipitate was washed three times with anhydrous ethanol and dried in an oven at 60°C. The precipitate was sieved through a 120-mesh sieve to obtain red date resistant starch (encapsulated and stored in a desiccator).

[0036] Example 3 This embodiment provides a method for preparing resistant starch, the preparation method comprising the following steps: (1) Soaking: After removing the core of fresh red dates, soak them in water for 12 hours, wash them with water, remove impurities, and obtain clean red dates; (2) grinding: cutting the clean red dates into small pieces, adding 6 times the amount of water and grinding for 3 times, collecting and obtaining a first slurry; (3) sugar removal: adding yeast in an amount of 4% by weight of red dates to the first slurry, introducing air and stirring continuously to remove sugar from the first slurry, and the slurry from which sugar is removed is the second slurry; (4) Protein removal: The pH of the second slurry was adjusted to neutral, and 600 U / g of neutral protease was added to remove protein (the temperature was maintained at 45° C.), and then the slurry was centrifuged at 3500 r / min for 15 min to obtain a precipitate; the precipitate was washed with distilled water for 3 times, and then dried in an oven at 50° C., crushed, and passed through a 100-mesh sieve to obtain red date starch; (5) Gelatinization: the red date starch was added into water to control the concentration to 20 wt %, and fully gelatinized in an ultrasonic pressure cooker at 120 W power and 121° C. for 45 min; (6) Acid hydrolysis: then add a 50 wt% hydrochloric acid-acetic acid solution to adjust the pH to 4.0, then add a potassium hydrogen phthalate-sodium hydroxide buffer solution, and stir thoroughly to obtain a gelatinized acid-hydrolyzed starch emulsion; (7) Debranching: placing the gelatinized acid-hydrolyzed starch milk in a constant temperature water bath at 55° C., adding a mixture of 1 wt % NaOH solution and 0.5 wt % KOH solution to adjust the pH to 6.0, then adding 150 U / g pullulanase and 20 U / g mesophilic α-amylase to fully debranch for 4 h, and after completion, inactivating the enzymes in a boiling water bath to obtain debranched starch milk; (8) Heating and retrograding: heating the debranched starch emulsion at a microwave power of 600 W and an infrared heating power of 600 W for 6 min while stirring; then standing at 4° C. for 30 h for aging and retrogradation to obtain retrograded starch emulsion; (9) Purification: 150 U / g of glucosidase was added to the retrograded starch milk to enzymatically hydrolyze the non-resistant starch, and then the mixture was centrifuged at 3500 r / min for 15 min and the supernatant was discarded. The precipitate was washed three times with anhydrous ethanol and dried in an oven at 60°C. The precipitate was sieved through a 100-mesh sieve to obtain red date resistant starch (encapsulated and stored in a desiccator).

[0037] Example 4 This embodiment provides a method for preparing resistant starch, the preparation method comprising the following steps: (1) Soaking: After removing the core of fresh red dates, soak them in water for 16 hours, wash them with water, remove impurities, and obtain clean red dates; (2) grinding: cutting the clean red dates into small pieces, adding 9 times the amount of water and grinding for 3 times, collecting and obtaining a first slurry; (3) sugar removal: adding yeast in an amount of 3% by weight of red dates to the first slurry, introducing air and stirring continuously to remove sugar from the first slurry, and the slurry from which sugar is removed is the second slurry; (4) Protein removal: The pH of the second slurry was adjusted to neutral, and 800 U / g of neutral protease was added to remove protein (the temperature was maintained at 45° C.), and then the slurry was centrifuged at 3500 r / min for 15 min to obtain a precipitate; the precipitate was washed with distilled water for 3 times, and then dried in an oven at 50° C., crushed, and passed through a 120-mesh sieve to obtain red date starch; (5) Gelatinization: the red date starch was added into water to control the concentration to 25 wt %, and fully gelatinized in an ultrasonic pressure cooker at 80 W power and 121° C. for 60 min; (6) Acid hydrolysis: then add a 50 wt% hydrochloric acid-acetic acid solution to adjust the pH to 4.0, then add a potassium hydrogen phthalate-sodium hydroxide buffer solution, and stir thoroughly to obtain a gelatinized acid-hydrolyzed starch emulsion; (7)Debranching: Place the gelatinized and acid-hydrolyzed starch milk in a constant temperature water bath at 60 °C, and add a mixture of 1 wt% NaOH solution and 0.5 wt% KOH solution to adjust the pH to 6.0. Then add 200 U / g of pullulanase and 25 U / g of medium-temperature α-amylase for sufficient debranching for 4 h. After completion, inactivate the enzyme in a boiling water bath to obtain debranched starch milk; (8)Heating and retrogradation: Heat the debranched starch milk at a microwave power of 600 W and an infrared heating power of 800 W for 8 min, stirring while heating; then let it stand at 4 °C for 36 h for aging and retrogradation to obtain retrograded starch milk; (9)Purification: Add 200 U / g of glucosidase to the retrograded starch milk to enzymatically hydrolyze non-resistant starch, then centrifuge at 3500 r / min for 15 min and discard the supernatant. Wash the precipitate 3 times with absolute ethanol, place it in an oven at 60 °C for drying, and pass it through a 120-mesh sieve to obtain jujube resistant starch (seal and store in a desiccator).

[0038] Example 5 This example provides a method for preparing resistant starch, and the preparation method includes the following steps: (1)Soaking: After removing the pits from fresh jujubes, soak them in water for 20 h, wash them with water, and remove impurities to obtain clean jujubes; (2)Grinding: Cut the clean jujubes into small pieces, add 5 times the amount of water, and grind them 3 times to collect and obtain the first slurry; (3)Sugar removal: Add 5% of the mass of yeast in jujubes to the first slurry, introduce air and stir continuously to remove the sugar in the first slurry. The slurry after sugar removal is the second slurry; (4)Protein removal: Adjust the pH of the second slurry to neutral, and add 1000 U / g of neutral protease to remove proteins (keep the temperature at 50 °C). Then centrifuge the slurry at 3500 r / min for 15 min to obtain a precipitate; wash the precipitate 3 times with distilled water, then dry it in an oven at 50 °C, pulverize it, and pass it through a 100-mesh sieve to obtain jujube starch; (5)Gelatinization: Add the jujube starch to water, control the concentration to 30 wt%, and fully gelatinize it at a power of 120 W and 121 °C in an ultrasonic pressure cooker for 75 min; (6)Acid hydrolysis: Then add a 75 wt% hydrochloric acid - acetic acid solution to adjust the pH to 3.0, and then add a potassium hydrogen phthalate - sodium hydroxide buffer solution, and stir well to obtain gelatinized and acid-hydrolyzed starch milk; (7) Debranching: Place the gelatinized and acid-hydrolyzed starch milk in a 60°C constant temperature water bath, add a mixed solution of 1 wt% NaOH solution and 0.5 wt% KOH solution to adjust the pH to 6.0, then add 250 U / g of pullulanase and 30 U / g of medium-temperature α-amylase for sufficient debranching for 4 h. After completion, inactivate the enzyme in a boiling water bath to obtain debranched starch milk; (8) Heating and retrogradation: Heat the debranched starch milk at a microwave power of 900 W and an infrared heating power of 1000 W for 10 min, stirring while heating; then let it stand at 4°C for 42 h for aging and retrogradation to obtain retrograded starch milk; (9) Purification: Add 250 U / g of glucosidase to the retrograded starch milk to enzymatically hydrolyze non-resistant starch, then centrifuge at 3500 r / min for 15 min and discard the supernatant. Wash the precipitate 3 times with absolute ethanol, place it in a 60°C oven for drying, and pass it through a 100-mesh sieve to obtain red date resistant starch (seal and store in a desiccator).

[0039] Example 6 This example provides a method for preparing resistant starch, and the preparation method includes the following steps: (1) Soaking: After removing the pits from fresh red dates, soak them in water for 24 h, wash them with water, and remove impurities to obtain clean red dates; (2) Pulping: Cut the clean red dates into small pieces, add 5 times the amount of water for pulping 3 times, and collect and obtain the first slurry; (3) Sugar removal: Add 3.5% of the mass of yeast in red dates to the first slurry, introduce air and stir continuously to remove the sugar in the first slurry. The slurry after sugar removal is the second slurry; (4) Protein removal: Adjust the pH of the second slurry to neutral, add 1200 U / g of neutral protease to remove proteins (keep the temperature at 50°C), then centrifuge the slurry at 3500 r / min for 15 min to obtain a precipitate; Wash the precipitate 3 times with distilled water, then dry it in a 50°C oven, pulverize it, and pass it through a 100-mesh sieve to obtain red date starch; (5) Gelatinization: Add the red date starch to water, control the concentration to 35 wt%, and fully gelatinize it at 80 W power and 121°C in an ultrasonic pressure cooker for 90 min; (6) Acid hydrolysis: Then add a 75 wt% hydrochloric acid - acetic acid solution to adjust the pH to 3.0, and then add a potassium hydrogen phthalate - sodium hydroxide buffer solution, and stir well to obtain gelatinized and acid-hydrolyzed starch milk; (7) Debranching: Place the gelatinized and acid-hydrolyzed starch milk in a 60 °C constant temperature water bath, add a mixed solution of 1 wt% NaOH solution and 0.5 wt% KOH solution to adjust the pH to 6.0, then add 300 U / g of pullulanase and 35 U / g of medium-temperature α-amylase for sufficient debranching for 4 h. After completion, inactivate the enzyme in a boiling water bath to obtain debranched starch milk; (8) Heating and retrogradation: Heat the debranched starch milk at a microwave power of 900 W and an infrared heating power of 1200 W for 12 min, stirring while heating; then let it stand at 4 °C for 48 h for aging and retrogradation to obtain retrograded starch milk; (9) Purification: Add 300 U / g of glucosidase to the retrograded starch milk to enzymatically hydrolyze non-resistant starch, then centrifuge at 3500 r / min for 15 min and discard the supernatant. Wash the precipitate 3 times with absolute ethanol, place it in a 60 °C oven for drying, and pass it through a 100-mesh sieve to obtain jujube resistant starch (seal and store in a desiccator).

[0040] Verification Example Detect the contents of RDS (rapidly digestible starch), SDS (slowly digestible starch), and RS (resistant starch) of the jujube resistant starch prepared in Examples 1 to 6: Take 200 mg of the prepared jujube resistant starch in a 15 mL round-bottom centrifuge tube, add 4 mL of deionized water and 4 mL of sodium acetate buffer with a pH of 5.2, and add a magnetic stir bar. Place the mixture in a 37 °C water bath and shake continuously for 30 minutes.

[0041] Add 2 mL of the enzyme mixture to the above mixed solution. The enzyme mixture is prepared as follows: Dissolve 4.5 g of pancreatin (A3176, ≥5 U / mg) in 40 mL of deionized water and centrifuge at 5000 r / min for 10 min. Take 27 mL of the supernatant and mix it with 3.2 mL of amyloglucosidase (10115, ≥70 U / mg).

[0042] Subsequently, pipette 0.1 mL of an aliquot from the mixture and add it to the ethanol solution at 0, 20, and 120 min. Centrifuge the mixture, and use Megazyme's GOPOD kit to detect the absorbance of the supernatant at 510 nm. Calculate the contents of RDS, SDS, and RS using the following formula: RDS (%) = (G 20 - G 0 ) × 0.9 / W SDS (%) = (G 120 - G 20 ) × 0.9 / W RS (%) = 100% - RDS% - SDS% Where G 0 、G20 and G 120 represent the absorbance at 510 nm at the 0th, 20th, and 120th minutes respectively, and W represents the weight of the starch sample.

[0043] Table 1 shows the RDS, SDS, and RS contents of the red date resistant starch prepared in Examples 1 to 6.

[0044] Table 1

[0045] It can be seen from Table 1 that in Example 6, the raw material ratio is moderate and the processing parameters are moderate, and the prepared resistant starch has the highest content.

[0046] Commercially available 1: Manufacturer: Hebei Qiansheng Biotechnology Co., Ltd., Product Name: Resistant Starch Commercially available 2: Manufacturer: Xi'an Kangnuo Chemical Co., Ltd., Product Name: Resistant Starch Furthermore, taking Example 6 as the object, further detection and characterization are carried out as follows: From Figure 3 it can be seen that: the surface of the red date starch granules is relatively smooth and the shape is relatively regular.

[0047] From Figure 4 it can be seen that: compared with the red date starch granules, the red date resistant starch granules also have relatively complete and larger granules, the surface becomes rough with small protrusions, and the shape becomes irregular.

[0048] From Figure 5 it can be seen that: the red date resistant starch has a diffraction peak near 17°, and the red date starch has diffraction peaks near 6°, 14°, 17°, 20°, 21°, and 24°. From this, it can be seen that the red date resistant starch shows a higher crystallinity and has a more stable crystal structure, increasing the stability of the double helix structure.

[0049] From Figure 6 it can be seen that: the red date resistant starch and the red date starch both have hydroxyl groups, carbon-carbon bonds, and carbonyl bonds at wavelengths of 3500 cm -1 , 2800 cm -1 , 1680 cm -1 . The red date resistant starch and the red date starch are consistent in the structure of chemical substances, indicating that the two are the same substance.

[0050] From Figure 7 it can be seen that: the red date resistant starch is more difficult to decompose by heat than the red date starch, which is in line with the characteristic of high crystallinity of the resistant starch.

[0051] From Figure 8 it can be seen that: the swelling rate of the red date resistant starch is lower than that of the red date starch.

[0052] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims described above.

Claims

1. A method for preparing resistant starch, characterized in that: The preparation method comprises the following steps: (1) Soaking: After removing the core of fresh red dates, soak them in water, wash them with water, remove impurities, and obtain clean red dates; (2) grinding: cutting the clean red dates into small pieces, adding water for grinding, and collecting and obtaining a first slurry; (3) sugar removal: adding yeast to the first slurry, introducing air and continuously stirring to remove sugar from the first slurry, wherein the slurry from which sugar is removed is the second slurry; (4) removing protein: adjusting the pH of the second slurry to neutral, adding neutral protease to remove protein, and then centrifuging the slurry to obtain a precipitate; washing, drying, crushing, and sieving the precipitate in sequence to obtain red date starch; (5) Gelatinization: adding the red date starch to water and gelatinizing it under ultrasound, high temperature and high pressure conditions; (6) Acid hydrolysis: then add hydrochloric acid-acetic acid solution to adjust the pH to acidic, then add potassium hydrogen phthalate-sodium hydroxide buffer solution, and stir thoroughly to obtain gelatinized acid-hydrolyzed starch milk; (7) debranching: adding alkali solution, pullulanase and mesophilic α-amylase to the gelatinized acid-hydrolyzed starch milk to perform debranching, and then inactivating the enzyme to obtain debranched starch milk; (8) Heating and retrograding: subjecting the debranched starch emulsion to a microwave-infrared heating treatment, and then allowing it to stand for aging and retrogradation to obtain retrograded starch emulsion; (9) Purification: adding glucosidase to the retrograded starch milk to enzymatically hydrolyze the non-resistant starch, then centrifuging and discarding the supernatant, washing, drying and sieving the precipitate in sequence, thereby obtaining red date resistant starch.

2. The method for preparing resistant starch according to claim 1, characterized in that: In step (1), the soaking time is 4 to 24 hours; And / or, in step (2), the mass of the added water is 5 to 10 times the mass of the pure red dates.

3. The method for preparing resistant starch according to claim 1, characterized in that: In step (3), the amount of yeast added is 2-5% of the mass of red dates.

4. The method for preparing resistant starch according to claim 1, characterized in that: In step (4), the amount of neutral protease added is 200-1200 U / g; and / or, after adding the neutral protease, maintaining the temperature of the slurry at 37-50° C. during the process of removing the protein; And / or, the centrifugal speed is 3000-3500 r / min, and the centrifugal time is 15-20 min; And / or, the drying temperature is 50-55°C; And / or, the sieving is through a 100-120 mesh sieve.

5. The method for preparing resistant starch according to claim 1, characterized in that: In step (5), the red date starch is added into water, and the concentration of the red date starch is maintained at 10-35 wt %; And / or, the conditions of ultrasound and high temperature and high pressure are: ultrasound power is 80-240W, high temperature is 121°C, and high pressure is 1.0-1.2MPa; And / or, the gelatinization time is 15 to 90 minutes.

6. The method for preparing resistant starch according to claim 1, characterized in that: In step (6), the concentration of the hydrochloric acid-acetic acid solution is 25-75 wt %; And / or, add hydrochloric acid-acetic acid solution to adjust the pH to 3-5, and keep the pH less than 5 during the acid hydrolysis process.

7. The method for preparing resistant starch according to claim 1, characterized in that: In step (7), the alkali solution is a mixture of 1 wt% NaOH solution and 0.5 wt% KOH solution; And / or, the added amount of the pullulanase is 50-300 U / g; And / or, the addition amount of the medium temperature α-amylase is 10~35U / g; And / or, the debranching temperature is 50-60° C., and the debranching time is 4 hours.

8. The method for preparing resistant starch according to claim 1, characterized in that: In step (8), the power of the microwave heating is 300-900 W; And / or, the wavelength of the infrared heating is 2-10 μm, and the power of the infrared heating is 200-1200 W; and / or, the microwave-infrared heating time is 2 to 12 minutes; And / or, the aging recovery temperature is 4° C. and the time is 18 to 48 hours.

9. The method for preparing resistant starch according to claim 1, characterized in that: In step (9), the amount of glucosidase added is 50-300 U / g; And / or, the centrifugal speed is 3000-3500 r / min, and the centrifugal time is 15-20 min; And / or, the drying temperature is 60-65°C; And / or, the sieving is through a 100-120 mesh sieve.

10. The resistant starch obtained by the preparation method according to any one of claims 1 to 9.

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