Preparation method and application of millet resistant starch

Abstract

The present application discloses a preparation method and application of millet resistant starch, which belongs to the field of starch modification technology. The preparation method provided in the present application is to pre-gelatinize millet starch, subject it to autoclave treatment, add pullulanase for enzymolysis reaction, cool it to room temperature, subject it to electron beam irradiation treatment, and subject it to low-temperature aging treatment, take it out and dry, crush and sieve it to obtain millet resistant starch. The present application treats millet starch by a composite modification method combining chemistry and physics, which can change the structure and length distribution of millet starch, and produce a large number of straight-chain starch molecules and cause molecular rearrangement, which can make the highest increase rate of resistant starch in millet starch reach 220%, further improving the high-value utilization of millet; at the same time, the preparation method is simple to operate, green and environmentally friendly, easy to mass produce, and can be widely used in the preparation of food processing products.

Description

Technical Field

[0001] The present application belongs to the technical field of starch modification, and in particular relates to a preparation method and application of millet resistant starch. Background Art

[0002] Millet, also known as millet or millet, is rich in starch, functional active ingredients, dietary fiber, essential amino acids and various trace elements for the human body, so it has great development value and economic benefits. At the same time, resistant starch is a type of starch that can enter the colon and be fermented and degraded by intestinal microorganisms to produce short-chain fatty acids. It has the functions of preventing diabetes, lowering blood lipids, and maintaining intestinal function.

[0003] The commonly used starch modification methods are physical, chemical and biological methods, and many effective modification methods are used to increase the resistant starch content. Generally speaking, starch from different sources and different modification methods may lead to many differences in starch structure. These differences will further affect the digestion, absorption and metabolism of starch in the human body, resulting in different physiological and health effects.

[0004] However, there is a lack of research on millet resistant starch, too few methods and low improvement rate of modified resistant starch after modification. Therefore, it is necessary to develop a new preparation method to prepare millet resistant starch. Summary of the invention

[0005] The present application discloses a preparation method and application of millet resistant starch, aiming to increase the content and improvement rate of the modified millet resistant starch.

[0006] In order to achieve the above purpose, the technical solution of this application is:

[0007] The first aspect of the present application provides a method for preparing millet resistant starch, the method comprising:

[0008] After the millet starch is pre-gelatinized, it is subjected to a heat and pressure cycle treatment to prepare a primary modified millet starch;

[0009] Adding pullulanase to the primary modified millet starch for enzymolysis reaction, after the reaction is completed, killing the enzyme in a boiling water bath, and cooling to room temperature to obtain a secondary modified millet starch;

[0010] The second modified millet starch is subjected to electron beam irradiation treatment to obtain third modified millet starch;

[0011] The thrice-modified millet starch is aged at low temperature, taken out and dried, crushed and sieved to obtain millet resistant starch.

[0012] In combination with the first aspect, preferably, when the millet starch is pregelatinized, the pregelatinization temperature is 80-90° C. and the time is 10 min;

[0013] In combination with the first aspect, preferably, during the autoclave cycle treatment, the treatment temperature is 4-121° C. and the treatment is cycled 2-5 times. The treatment time at low temperature is 24 hours, and the treatment time at high temperature is 10-30 minutes.

[0014] In combination with the first aspect, preferably, the pullulanase is added in an amount of 10-50 U / g, and the enzymatic reaction time is 3-15 h.

[0015] In combination with the first aspect, preferably, when the secondary modified millet starch is subjected to electron beam irradiation treatment, the output energy of the electron beam is 10 MeV, the scanning frequency is 200-300 pps, and the effective absorbed dose of the electron beam irradiation is 5-15 kGy.

[0016] In combination with the first aspect, preferably, the thrice-modified millet starch is aged at a low temperature of 2-6°C for 5-48 hours.

[0017] The second aspect of the present application provides millet resistant starch prepared by the preparation method of millet resistant starch described in the first aspect.

[0018] The third aspect of the present application provides the use of the millet resistant starch described in the second aspect in food processing products.

[0019] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0020] The preparation method provided in the present application prepares millet resistant starch by a composite modification method of autoclave-enzymatic cycle-electron beam irradiation-low temperature aging. Among them, the molecular chain of millet starch is opened by gelatinization treatment, and then the autoclave treatment is carried out. Through the synergistic effect of the two, the millet starch absorbs water and swells, the particle morphology and crystal structure are destroyed and rearranged in a direction, and the starch molecules are released from the inside of the particles, so that the millet starch is regenerated, thereby providing a basis for increasing the content of resistant starch; then, pullulanase is added for enzymatic reaction, which can cut off the α-1,6 glycosidic bond in the branch point of the amylose, and then cut off the branch structure, producing a large number of free amylose molecules, and further the electron free radicals irradiated by the electron beam rearrange and recouple the molecular chain, and then after low temperature aging treatment, the starch molecules are easy to be connected by hydrogen bonds or van der Waals forces to form straight-chain structure molecules, and promote the formation of a large number of crystal nuclei and promote the growth of crystals, thereby greatly increasing the content of resistant starch in millet starch.

[0021] The present application processes millet starch by combining chemical modification with physical modification, which can increase the content of resistant starch in millet starch by up to 220%, further improving the high-value utilization of millet; at the same time, the preparation method is simple to operate, green and environmentally friendly, low in cost, and easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A1-broomcorn resistant starch prepared in the examples of the present application is a graph showing the effect of different pullulanase addition amounts on the resistant starch content after modification;

[0024] Figure 2 A1-broomcorn resistant starch prepared in the examples of the present application is a graph showing the resistant starch content after modification at different enzymatic hydrolysis times;

[0025] Figure 3 A1-broomcorn millet resistant starch prepared in the examples of the present application is a graph showing the resistant starch content after modification at different autoclave times;

[0026] Figure 4 A graph showing the content of modified resistant starch of A1-broomcorn millet resistant starch prepared in the examples of the present application at different refrigeration times;

[0027] Figure 5 This is a comparison chart of the transparency of the A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0028] Figure 6 This is a comparison chart of the water solubility of the A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0029] Figure 7 This is a comparison chart of the swelling power of the A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0030] Figure 8 This is a comparison chart of freeze-thaw stability of A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0031] Fig. 9 This is a comparison chart of the particle size of the A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0032] Fig.10 This is a comparison chart of some texture properties of A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification;

[0033] Fig.11 This is the XRD diagram of the A1-broomcorn millet resistant starch prepared in the examples of the present application before and after modification. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0036] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0037] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0038] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0039] It should be noted that all raw materials and reagents in the examples of the present application are purchased on the market or prepared according to conventional methods well known to those skilled in the art. For example, millet starch, pullulanase, etc. are purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0040] In a first aspect, the present application provides a method for preparing millet resistant starch, the method comprising:

[0041] After the millet starch is pre-gelatinized, it is subjected to a heat and pressure cycle treatment to prepare a primary modified millet starch;

[0042] Adding pullulanase to the primary modified millet starch for enzymolysis reaction, after the reaction is completed, killing the enzyme in a boiling water bath, and cooling to room temperature to obtain a secondary modified millet starch;

[0043] The second modified millet starch is subjected to electron beam irradiation treatment to obtain third modified millet starch;

[0044] The thrice-modified millet starch is aged at low temperature, taken out and dried, crushed and sieved to obtain millet resistant starch.

[0045] The molecular chains of millet starch are opened by gelatinization treatment, and then the millet starch is subjected to pressure heat cycle treatment. Through the synergistic effect of the two, the millet starch absorbs water and swells, the particle morphology and crystal structure are destroyed and directionally rearranged, and the starch molecules are released from the inside of the particles, so that the millet starch is regenerated, thereby providing a basis for increasing the content of resistant starch; then, pullulanase is added for enzymatic hydrolysis, which can cut the α-1,6 glycosidic bonds in the branch points of amylose, and then cut off the branch structure to produce a large number of free amylose molecules, which are further irradiated by electron beams. The electron free radicals After rearrangement and re-coupling, and then subjected to low-temperature aging treatment, the starch molecules are easily connected through hydrogen bonds or van der Waals forces to form straight-chain structure molecules, and the formation of a large number of crystal nuclei is promoted and the growth of crystals is promoted, thereby greatly increasing the content of resistant starch in millet starch; the present application treats millet starch through a combination of chemical modification and physical modification, which can increase the content of resistant starch in millet starch by up to 220%, further improving the high-value utilization of millet; at the same time, the preparation method is simple to operate, green and environmentally friendly, low in cost, and easy to mass produce.

[0046] It should be noted that, specifically, the japonica millet starch used in this application is subjected to alkali-modified extraction treatment, 100 g of millet is weighed, and a NaOH solution with a mass fraction of 0.3% is added according to a solid-liquid ratio of 1:10 for soaking; soaking at 35°C for 20 hours, crushing the millet with a high-speed disperser, and using a 200-mesh sieve to remove crude fiber and other impurities to obtain a starch slurry; centrifuging to discard the supernatant, scraping off the yellowish-brown soft layer on the upper layer of the precipitate, adding 1:3 distilled water and stirring evenly, and adjusting the pH to 7.0 with 1 mol / L HCl; centrifuging again, and then washing the starch precipitate 3 times with 1:2 distilled water to remove protein and various ions in the starch; finally, the obtained wet starch is placed in an oven at 32°C and dried for 20 hours, crushed, and passed through a 100-mesh sieve to obtain millet starch with higher purity.

[0047] In the embodiment of the present application, when the millet starch is pregelatinized, the pregelatinization temperature is preferably 80-90°C, such as 80°C, 85°C, 90°C or any temperature within the range, and the time is preferably 10 minutes. Among them, the method of pregelatinizing millet starch adopted in the present application is: suspending millet starch in distilled water to obtain a 20% (or 100g / L) starch suspension, and pregelatinizing at 85°C for 15 minutes; wherein, the millet starch is swollen, split, and formed into a uniform paste solution in water, so that the hydrogen bonds between the crystalline and amorphous starch molecules in the millet starch are broken, and dispersed in water to form a colloidal solution, thereby improving the dispersibility and stability of starch, thereby providing a basis for the subsequent improvement of resistant starch.

[0048] In the embodiment of the present application, when subjected to the autoclave treatment, the treatment temperature is 4-121°C and the treatment is repeated 2-5 times, the treatment time at low temperature is 24h, and the treatment time at high temperature is 10-30min, for example, 10min, 15min, 20min, 25min, 30min or any time within the range. Among them, the autoclave treatment of millet starch can change the internal crystalline structure of starch and the arrangement of starch chains inside the granules, dissolve the straight-chain starch, reduce the chain length of some long-chain starch molecules, and reduce the viscosity of millet starch, so that the straight-chain starch molecules are fully extended, and the straight-chain starch molecules move around and recombine, thereby increasing the content of resistant starch. Among them, the autoclave treatment includes: after the millet starch is pre-gelatinized, it is cooled to 4°C and placed, and then placed in a 121°C hot environment, which is the first cycle to obtain product C1; C1 is cooled to 4°C and placed, and then placed in a 121°C hot environment, which is the second cycle to obtain product C2; and so on, a total of 2-5 cycles, preferably 3 cycles.

[0049] In the embodiment of the present application, the addition amount of the pullulanase is preferably 10-50U / g, for example, 10U / g, 20U / g, 30U / g, 40U / g, 50U / g or any value within this range; the time of the enzymatic reaction is preferably 3-15h, for example, 3h, 6h, 9h, 12h, 15h or any time within this range. Among them, the present application controls the addition amount of pullulanase and the time of the enzymatic reaction to saturate the combination of millet starch and pullulanase, so that the debranching reaction tends to equilibrium, and the enzymatic reaction will not continue to increase the addition amount of the enzyme and extend the time, and the amylose content will no longer rise, so that the debranching reaction tends to equilibrium, thereby increasing the content of resistant starch.

[0050] It should be noted that the enzyme inactivation treatment in a boiling water bath can inactivate the pullulanase, prevent the remaining pullulanase from affecting the subsequent links, and create a mild cooling environment to prevent sudden cooling and heating from causing unpredictable changes in starch. The gradual cooling process is conducive to the rearrangement of starch molecular chains, allowing starch molecules to form a dense spatial structure.

[0051] In the embodiment of the present application, when the secondary modified millet starch is subjected to electron beam irradiation treatment, the output energy of the electron beam is 10MeV, the scanning frequency is preferably 200-300pps, and the effective absorbed dose of electron beam irradiation is 5-15kGy. Wherein, by electron beam irradiation treatment, the electron free radicals generated rearrange and recouple the free molecular chains after enzymatic hydrolysis, thereby improving the grafting efficiency of starch, and then producing a large number of linear structure molecules, and increasing the content of resistant starch. In addition, the use of electron beam irradiation also has the advantages of safety, energy saving, time saving, environmental protection, easy quality control, simple operation, and convenience for large-scale industrial production and application.

[0052] In the embodiment of the present application, the three modified millet starch is aged at low temperature, and the temperature is preferably 2-6°C, for example, 2°C, 3°C, 4°C, 5°C, 6°C or any temperature within the range, and the time is preferably 5-48h, for example, 5h, 15h, 25h, 35h, 48h or any time within the range. Among them, by undergoing another crystallization process during the aging treatment at low temperature, the starch molecules are easily connected by hydrogen bonds or van der Waals forces to form linear structure molecules, and promote the formation of a large number of crystal nuclei and promote the growth of crystals, thereby greatly increasing the content of resistant starch in millet starch. By further aging treatment at low temperature, the freely curled straight-chain starch molecules are brought closer to each other, and a tighter double helix structure is formed through intermolecular hydrogen bonds, and the small double helix continues to grow into larger straight-chain starch crystals, thereby improving the stability of resistant starch.

[0053] The second aspect of the present application provides millet resistant starch prepared by the preparation method of millet resistant starch described in the first aspect, wherein the millet resistant starch has a high millet resistant starch content and the increase rate of the resistant starch content can reach up to 220%.

[0054] The third aspect provides the use of the millet resistant starch described in the second aspect in the preparation of food processing products. The millet resistant starch prepared has a high millet resistant starch content and the increase rate of the resistant starch content can reach up to 220%, so that it has a wide range of applications in food processing products.

[0055] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0056] Example 1

[0057] This embodiment provides a method for preparing A1-broomcorn millet resistant starch, which specifically comprises:

[0058] S101: suspending millet starch in distilled water to obtain a 20% (or 100 g / L) starch suspension, pre-gelatinizing at 85° C. for 15 min; cooling to room temperature, refrigerating at 4° C. for 24 h, heating in an autoclave at 121° C., refrigerating at 4° C. for 24 h, heating to 121° C., repeating the process for 3 times, and cooling to about the optimal temperature for enzyme reaction;

[0059] S102: Add pullulanase and perform enzymolysis in a constant temperature water bath at 60°C. After the reaction, inactivate the enzyme in boiling water for 10 minutes and cool to room temperature.

[0060] S103: subjecting the enzymatically hydrolyzed starch to electron beam irradiation treatment, with an irradiation dose of 10 kGy;

[0061] S104: The treated starch is placed in a refrigerator at 4°C for refrigeration, taken out and placed in a constant temperature drying oven at 35°C for drying to constant weight, and crushed through a 0.150 mm (100 mesh) sieve to obtain A1-broomcorn resistant starch.

[0062] In order to illustrate the technical effect of the modification method of the present application, the inventors first used a single factor experimental method to study the effects of pullulanase addition (A), enzymolysis time (B), autoclave time (C), and refrigeration time (D) on millet starch modification, and determined the optimal values ​​of each index. The single factor experiment is shown in Table 1.

[0063] Table 1 Single factor experimental design table

[0064]

[0065] The single factor test results of this example are as follows Figure 1-4 As shown. Among them, Figure 1 This is the graph showing the effect of different pullulanase addition amounts on the content of modified resistant starch; Figure 2 The graph of the effect of different enzymatic hydrolysis times on the content of modified resistant starch; Figure 3 This is a graph showing the effect of different autoclave times on the content of modified resistant starch; Figure 4 This is a graph showing the effect of different refrigeration times on the content of modified resistant starch.

[0066] according to Figure 1 It can be seen that with the increase of the amount of pullulanase added, the resistant starch content first increases and then decreases. When the pullulanase addition amount is 40U / g, the resistant starch content reaches the highest value. Thereafter, as the pullulanase addition amount continues to increase, the resistant starch content decreases rapidly. Therefore, this application selects a pullulanase addition amount of 40U / g.

[0067] according to Figure 2It can be seen that with the increase of enzymatic hydrolysis time, the resistant starch content first increases and then decreases. When the enzymatic hydrolysis time is 12 hours, the resistant starch content reaches the highest value. After that, as the enzymatic hydrolysis time continues to increase, the resistant starch content decreases rapidly. Therefore, this application chooses to carry out modification when the enzymatic hydrolysis time is 12 hours.

[0068] according to Figure 3 It can be seen that when the pressing time is 15 minutes, the resistant starch content reaches the maximum value. After that, as the pressing time continues to increase, the resistant starch content gradually decreases. Therefore, this application chooses to carry out modification when the pressing time is 15 minutes.

[0069] according to Figure 4 It can be seen that when the refrigeration time is 36 hours, the resistant starch content reaches the maximum value. After that, as the refrigeration time continues to increase, the resistant starch content decreases rapidly. Therefore, this application chooses to carry out modification when the refrigeration time is 36 hours.

[0070] In order to verify the combined effect of the above-mentioned optimal value indicators, a three-level experiment with four factors including pullulanase addition amount (A), enzymatic hydrolysis time (B), autoclave time (C) and refrigeration time (D) was designed, as shown in Table 2.

[0071] Table 2 Four-factor three-level test table

[0072]

[0073] This application refers to the Megazyme total starch kit to determine the total starch content, the formula is as follows:

[0074] Starch (%) = ΔA × F × EV × D / W × 0.9

[0075] ΔA: The absorbance of the sample solution read by the control reagent blank minus the absorbance of the sample blank read by the control reagent blank;

[0076] F: GOPOD absorbance value obtained by dividing 100ug glucose by 100ug glucose;

[0077] EV: sample volume 10.2 mL;

[0078] D: diluted sample solution parameter 1;

[0079] W: Weigh the sample weight.

[0080] This application refers to the Megazyme resistant starch kit to determine the resistant starch content, the formula is as follows:

[0081] Resistant starch (%) = ΔA × F / W × 90

[0082] ΔA: absorbance of control reagent blank reading;

[0083] F: GOPOD absorbance value obtained by dividing 100 μg of glucose by 100 μg of glucose;

[0084] W: weigh the sample weight;

[0085] Table 3 Orthogonal experimental design and results

[0086]

[0087]

[0088] Therefore, the orthogonal test shows that the optimal process conditions are A1 B2 C2 D3, i.e., 30U / g enzyme addition, 12h enzymolysis time, 15min autoclave time, and 48h refrigeration time. After verification, the resistant starch content of the modified millet starch under this process condition is higher. It has been determined that the total starch content in the millet starch used in this application is 84.88%, the resistant starch content is 1.62%, and the resistant starch content of the millet starch made after modification is 5.20%. It can be seen that the resistant starch content of the japonica millet starch made after modification by this scheme can be increased by 220%.

[0089] In order to verify the changes in the physical and chemical properties of the millet starch prepared in the examples of the present application before and after modification, the present application tested and compared the physical and chemical properties of the millet starch before and after modification, and the test results are shown in Table 4.

[0090] Table 4 Comparison of physical and chemical properties of millet starch before and after modification

[0091]

[0092]

[0093] In order to verify the changes in the physicochemical properties of millet starch prepared in the present application example before and after modification, the test results are as follows: Figures 5 to 11 As shown; among them, Figure 5 This is a comparison chart of transparency before and after modification; Figure 6 This is a comparison chart of water solubility before and after modification; Figure 7 This is a comparison chart of expansion force before and after modification; Figure 8 This is a comparison chart of freeze-thaw stability before and after modification; Fig. 9 This is a comparison chart of particle size before and after modification; Fig.10 This is a comparison chart of some texture characteristics before and after modification; Fig.11 This is the XRD comparison diagram before and after modification.

[0094] according to Figure 5It can be seen that the transparency of the modified millet starch using the preparation method of the present application is significantly reduced, indicating that since the amorphous regions of the millet starch are recrystallized, the scattering of light by the aged starch increases, resulting in reduced transparency.

[0095] The test method for the water solubility and swelling power of starch in this application is as follows: suspend the starch in water, stir, heat and centrifuge, pour the liquid into an aluminum box of known weight, leave the starch precipitate, dry the supernatant and precipitate to constant weight, calculate the weight of the precipitated starch to obtain the swelling power, calculate the weight of the supernatant to obtain the water solubility.

[0096] Water solubility (%): W 2 / W 1 ×100

[0097] Expansion force (g / g): [W 3 / (W 1 -W 2 )]×100

[0098] Where W 1 is the mass of dry starch, W 2 is the mass of dry supernatant, W 3 is the weight of precipitated starch.

[0099] according to Figure 6 It can be seen that the water solubility of the modified millet starch is increased by the preparation method of the present application, indicating that after the composite modification method of autoclave-enzymatic hydrolysis, the structure of the millet starch is destroyed, allowing water to penetrate, thereby increasing the water solubility.

[0100] according to Figure 7 It can be seen that the preparation method of the present application significantly reduces the swelling force of the modified millet starch. After the millet starch particles are modified, the internal structure is relatively tight and difficult to absorb water, resulting in a smaller swelling degree.

[0101] according to Figure 8 It can be seen that the freeze-thaw stability of millet starch after modification is significantly increased by the preparation method of the present application. Freeze-thaw stability reflects the ability of millet starch molecules to maintain their original properties during freezing and thawing, and is also an important indicator for judging whether starch is suitable for making frozen foods. During the freeze-thaw process, millet starch molecules will undergo dehydration and shrinkage, and free water will precipitate. Therefore, the freeze-thaw stability of starch can be indirectly expressed by the water separation rate. The lower the water separation rate, the better the freeze-thaw stability of starch. Therefore, after modification, the freeze-thaw stability of millet resistant starch is significantly increased.

[0102] according to Fig. 9 and Fig.10It can be seen that the texture of the modified millet starch has changed significantly by using the preparation method of the present application; a 10% sample suspension was heated in boiling water, cooled to room temperature and stored. The gel was infiltrated twice at a speed of 1 mm / s with a flat cylindrical probe with a diameter of 10 mm to generate a force-time curve. According to the figure, the hardness, viscosity, chewiness, elasticity and cohesion have changed significantly after modification.

[0103] according to Fig.11 It can be seen that the present application conducted X-ray diffraction tests on starch before and after modification, and by comparing the XRD patterns before and after the test, the crystal structure of the starch changed significantly.

[0104] At the same time, in order to verify the comprehensive performance of the millet resistant starch prepared in the above examples, the present application provides the following comparative examples for detailed description.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing B1-broomcorn millet resistant starch, which specifically comprises:

[0107] S201: suspending millet starch in distilled water to obtain a 20% (or 100 g / L) starch suspension, and pre-gelatinizing at 85° C. for 15 min;

[0108] S202: adding pullulanase, performing enzymolysis in a constant temperature water bath at 60°C, inactivating the enzyme in boiling water for 10 minutes after the reaction, and cooling to room temperature;

[0109] S203: subjecting the enzymatically hydrolyzed starch to electron beam irradiation treatment, with an irradiation dose of 10 kGy;

[0110] S204: Refrigerate the treated starch in a refrigerator at 4°C, take it out and dry it in a constant temperature drying oven at 35°C to constant weight, and grind it through a 0.150 mm (100 mesh) sieve to obtain B1-broomcorn resistant starch.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing B2-broomcorn millet resistant starch, which specifically comprises:

[0113] S301: suspend millet starch in distilled water to obtain a 20% (or 100 g / L) starch suspension, pre-gelatinize at 85°C for 15 min; cool to room temperature, refrigerate at 4°C for 24 h, heat to 121°C in an autoclave, refrigerate at 4°C for 24 h, heat to 121°C, repeat the process 3 times, and cool to about the optimal temperature for enzyme reaction;

[0114] S302: Add pullulanase and perform enzymolysis in a constant temperature water bath at 60°C. After the reaction, inactivate the enzyme in boiling water for 10 minutes and cool to room temperature.

[0115] S303: Refrigerate the treated starch in a refrigerator at 4°C, take it out and dry it in a constant temperature drying oven at 35°C to constant weight, and grind it through a 0.150mm (100 mesh) sieve to obtain B2-broomcorn resistant starch.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing B3-broomcorn millet resistant starch, which specifically comprises:

[0118] S401: suspend millet starch in distilled water to obtain a 20% (or 100 g / L) starch suspension, pre-gelatinize at 85°C for 15 min; cool to room temperature, refrigerate at 4°C for 24 h, heat to 121°C in an autoclave, refrigerate at 4°C for 24 h, heat to 121°C, repeat the process 3 times, and cool to the optimal temperature for enzyme reaction;

[0119] S402: Add pullulanase and perform enzymolysis in a constant temperature water bath at 60°C. After the reaction, inactivate the enzyme in boiling water for 10 minutes and cool to room temperature.

[0120] S403: subjecting the enzymatically hydrolyzed starch to electron beam irradiation treatment, with an irradiation dose of 10 kGy;

[0121] S404: The treated starch is taken out and placed in a 35°C constant temperature drying oven to dry to constant weight, and then crushed and passed through a 0.150 mm (100 mesh) sieve to obtain B3-broomcorn resistant starch.

[0122] Table 5 Resistant starch content and improvement rate of prepared millet

[0123]

[0124] It can be seen from the data in the table that the difference between Comparative Example 1 of the present application and Example 1 is that no autoclave treatment is performed, so that the content of the prepared millet resistant starch is significantly reduced, and the improvement rate of its resistant starch is also significantly reduced; the difference between Comparative Example 2 of the present application and Example 1 is that no electron beam irradiation treatment is performed, so that the content of the prepared millet resistant starch is significantly reduced, and the improvement rate of its resistant starch is also significantly reduced; the difference between Comparative Example 3 of the present application and Example 1 is that no low-temperature aging treatment is performed, so that the content of the prepared millet resistant starch is significantly reduced, and the improvement rate of its resistant starch is also significantly reduced. Therefore, the preparation method provided in the present application prepares millet resistant starch by a composite modification method of autoclave treatment-enzymatic reaction-electron beam irradiation-low-temperature aging treatment, and through the synergistic effect between each step, the content of resistant starch in millet starch can be increased by up to 220%, thereby improving the high-value utilization of millet.

[0125] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0126] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions recorded in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing millet resistant starch, characterized in that: The method comprises: The millet starch was pre-gelatinized at 85°C for 15 min, cooled to room temperature, and then subjected to a hot-pressing cycle treatment, wherein the hot-pressing cycle treatment was: refrigerated at 4°C for 24 h, then heated to 121°C for 15 min, and the hot-pressing cycle treatment was repeated three times to prepare a modified millet starch; Adding 30 U / g pullulanase to the primary modified millet starch for enzymolysis reaction for 12 h, after the reaction is completed, inactivating the enzyme in a boiling water bath, and cooling to room temperature to obtain a secondary modified millet starch; The secondary modified millet starch is subjected to electron beam irradiation treatment, the irradiation dose is 10 kGy, the output energy of the electron beam is 10 MeV, and the scanning frequency is 200-300 pps to obtain the tertiary modified millet starch; The thrice-modified millet starch was aged at a low temperature of 4° C. for 48 h, taken out and dried, crushed and sieved to obtain millet resistant starch.

2. The millet resistant starch prepared according to the preparation method of millet resistant starch according to claim 1.

3. Application of the millet resistant starch according to claim 2 in food processing products.

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