Method for preparing slowly digestible starch by mixing modified protein and starch

Abstract

The invention discloses a method for preparing slowly digestible starch by mixing modified protein and starch. The method comprises the following steps: S1, dissolving protein in double distilled water to prepare a protein suspension; carrying out acid treatment on the protein; adjusting the pH value of the modified protein, dialyzing the suspension in double distilled water to remove residual salt ions and small molecular impurities, and then freeze-drying, hot-air drying and naturally drying to constant weight; s2, dissolving potato starch in double distilled water to obtain a starch emulsion, adding the modified protein into the starch emulsion, carrying out heat-moisture treatment, and then carrying out gelatinization treatment; and finally, performing freeze drying, hot air drying and natural drying on the compound, and grinding into powder. According to the invention, the digestion characteristic of the potato starch is obviously influenced by adding the modified protein, and particularly, the digestion rate of the starch is slowed down by changing the structure and interaction of a starch-protein compound; an effective regulation and control strategy is provided for improving the digestion characteristic of starch, and development of low-GI healthy food is facilitated.

Description

Technical Field

[0001] The invention relates to the field of food science and technology, and in particular to a method for preparing slowly digestible starch by mixing modified protein with starch. Background Art

[0002] As the main source of carbohydrates in the human diet, the digestibility of starch directly affects the body's absorption of energy and control of blood sugar levels. However, starchy foods often have a high glycemic index (GI), and excessive intake can lead to a rapid increase in blood sugar after a meal. Long-term excessive intake of high-GI starch is considered a potential factor in undermining human health and inducing a variety of metabolic diseases, especially obesity and type 2 diabetes.

[0003] At present, non-starch polysaccharides and polyphenols have obvious advantages in improving the physicochemical and in vitro digestibility of starch, but there are also some potential disadvantages, such as affecting the sensory properties and nutrient absorption of food. The high viscosity and anti-nutritional properties of non-starch polysaccharides may affect the taste and nutrient absorption of food. The addition of polyphenols may affect the color and flavor of food, and the sources are limited, making it difficult to produce industrially. Gluten, soy protein isolate, and zein, as natural plant proteins, have the potential to improve starch digestibility, and have the advantages of high nutritional value and wide sources. However, natural plant proteins have low solubility and may not be effective in reducing starch digestibility. The modified protein can release a variety of bioactive peptides, improve nutritional value, and interact with starch to a greater extent, inhibiting enzyme hydrolysis of starch, thereby reducing starch digestibility. Acid treatment modification of plant protein can improve its solubility and functional properties. In addition, modified protein reduces the starch digestion rate and affects human postprandial blood sugar by forming a physical barrier around starch granules. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing slowly digestible starch by mixing modified protein with starch, changing the conformation of the protein by acid treatment so that more groups are exposed to form a complex with starch, reducing the digestion rate of starch, and preparing starch with high slow digestibility, which helps the starch to be slowly digested in the human body, regulates the postprandial blood sugar level, and is conducive to the development of low GI healthy foods to meet the needs of specific health demand groups, so as to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preparing slowly digestible starch by mixing modified protein with starch, comprising the following steps:

[0006] S1 prepares modified protein: dissolves the protein in double distilled water to prepare a 3-4% protein suspension; performs acid treatment on the protein; adjusts the pH value of all modified proteins to 7.0, and then places the suspension in double distilled water, dialyzes at 0-4°C for 24-48h to remove residual salt ions and small molecular impurities, and then freeze-dries, hot-air dries, and naturally dries to constant weight to obtain acid-treated protein;

[0007] S2 Preparation of slowly digestible starch: potato starch is dissolved in double distilled water to obtain a starch emulsion with a concentration of 10%, modified protein is added to the starch emulsion at a ratio of 10-15% (w / w), treated under wet heat conditions, and then gelatinized; finally, the complex is freeze-dried, hot-air dried and naturally dried, ground into powder and passed through a 100-mesh sieve.

[0008] Preferably, the protein in step S1 is one of gluten, soy protein isolate and zein.

[0009] Preferably, the acid treatment in step S1 comprises: reacting in a 0.06-0.4 M acid solution at 65-75° C. for 16-20 h.

[0010] Preferably, the acidic solution is one of malic acid and citric acid.

[0011] Preferably, the wet heat treatment in step S2 includes: stirring in a 40-80° C. water bath for 1-1.5 hours to promote the formation of starch-protein complexes.

[0012] Preferably, the gelatinization treatment in step S2 comprises: raising the water bath temperature of the starch after the wet heat treatment to 90-95° C. for gelatinization treatment, and continuing the treatment for 10-20 minutes to ensure the gelatinization of the starch.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The invention significantly affects the digestion characteristics of potato starch by adding modified protein, especially slows down the digestion rate of starch by changing the structure and interaction of starch-protein complex; this provides an effective regulation strategy for improving the digestion characteristics of starch and helps to develop low GI healthy food.

[0015] The modified protein of the present invention changes its structure through acid treatment, increases its interaction ability with starch, and thus improves its composite index with starch; this structural change not only enhances the solubility of plant protein, but also improves its functional properties and increases its nutritional value; the present invention provides the food industry with a nutritious and widely available plant protein resource, which helps to promote the sustainable development of the food industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention provides a flow chart of a method for preparing slowly digestible starch by mixing modified protein with starch. DETAILED DESCRIPTION

[0017] In order to further explain the technical solution of the present invention, it is described in detail below through specific embodiments.

[0018] Example 1

[0019] Materials and Methods

[0020] 1) Materials

[0021] Potato starch, gluten, soy protein isolate, zein, pancreatin (8×USP), pepsin (30000U·g-1), amyloglucosidase (10,0000U·mL-1), malic acid, citric acid, sodium hydroxide, anhydrous ethanol.

[0022] 2) Main instruments

[0023] 7230G UV spectrophotometer, Shanghai Jingke Instrument Co., Ltd.; CTFD-12S-80℃ vacuum freeze drying, hot air drying and natural drying machine, Qingdao Yonghe Chuangxin Electronic Technology Co., Ltd.; ZD-85 constant temperature oscillator, Changzhou Aohua Instrument Co., Ltd.; DF-101 constant temperature heating magnetic stirrer, Gongyi Yuhua Instrument Co., Ltd.; TG16G, Hunan Keda Scientific Instrument Co., Ltd.

[0024] 3) Experimental methods

[0025] 3.1) Please refer to Figure 1 The present invention provides a method for preparing slowly digestible starch by mixing modified protein with starch, comprising the following steps:

[0026] S1: 4 g of gluten was accurately weighed and dissolved in 0.20 M malic acid solution to prepare a 4% protein suspension; acid treatment conditions: 70°C water bath, 200 rpm stirring, reaction for 20 h; 2 M NaOH was used to adjust the pH to 7.0 to terminate the acid treatment; the suspension was then placed in double distilled water and dialyzed at 4°C for 48 h with a molecular weight cutoff of 3,500 Da to remove residual salt ions and small molecular impurities, and finally freeze-dried, hot-air dried and naturally dried to constant weight to obtain acid-treated gluten;

[0027] S2: The modified gluten prepared in step 1 is mixed with potato starch at a ratio of 15% (w / w), and dissolved in double distilled water to obtain a starch-protein emulsion with a concentration of 10%; then the mixture is mixed under wet heat conditions (the wet heat treatment temperatures are 40, 50, 60, 70, and 80° C. in a water bath, and stirred at 200 rpm for 1 hour), and gelatinized at 95° C. for 15 minutes to obtain a starch-protein complex; the complex is freeze-dried, hot-air dried, and naturally dried, ground into powder, and sieved through a 100-mesh sieve to obtain the final products PS-MA-Glu40, PS-MA-Glu50, PS-MA-Glu60, PS-MA-Glu70, and PS-MA-Glu80.

[0028] 3.2) Determination of in vitro starch digestibility

[0029] First, the sample (200 mg) was mixed with deionized water (2 mL) and digested with pepsin solution (pepsin dissolved in 0.05 mol / L hydrochloric acid solution) in a constant temperature oscillator for 30 min. Then, 5 mL of sodium acetate buffer (0.05 mol / L, pH 5.2) was added, and after incubation for 30 min, 2 mL of enzyme mixture (pancreatin and glucoamylase) was added, and the reaction was continued for 0, 20 and 120 min. Finally, the hydrolyzate (1 mL) was taken, anhydrous ethanol solution (4 mL) was added to terminate the reaction, the solution was centrifuged, and the glucose content in the supernatant was determined using the 3,5-dinitrosalicylic acid (DNS) method. RDS, SDS and RS contents were calculated using the following formula:

[0030] RDS(%)=(G 20 -G0) / TS×0.9×100 (1)

[0031] SDS(%)=(G 120 -G 20 ) / TS×0.9×100 (2)

[0032] RS(%)=TS-RDS-SDS / TS×0.9×100 (3)

[0033] Wherein, G0 is the free glucose content in the starch suspension before hydrolysis (mg); G20 and G120 represent the glucose content (mg) produced by starch within 20min and 120min of hydrolysis, respectively; TS is the total starch content (mg); and 0.9 is the factor for the conversion of glucose into starch.

[0034] All the results were repeated at least three times and are shown in Table 1.

[0035] Table 1: RDS, SDS and RS contents of potato starch and its starch-protein complex.

[0036]

[0037]

[0038] As shown in Table 1, the compounding temperature has a significant effect on the digestibility of the PS-MA-Glu complex. With the increase of the compounding temperature, the rapidly digestible starch (RDS) content of the complex decreased significantly, the slowly digestible starch (SDS) content increased significantly, and there was no significant difference in the resistant starch (RS) content. The results show that the increase in the compounding temperature may enhance the interaction between modified gluten and starch, thereby changing the digestibility of starch and reducing its digestion rate. When the compounding temperature is in the range of 40℃ to 60℃, there is no significant difference in the RDS content of the complexes, but there is a difference in the SDS content. This may indicate that within this temperature range, modified gluten has a significant effect on the slowly digestible properties of starch, while the effect on the quickly digestible starch content is small. When the compounding temperature is further increased to 70℃ or 80℃, there is no significant difference in the digestibility of the complex, indicating that within this temperature range, the effect of modified gluten on the digestibility of starch may have reached saturation, which may be due to the high temperature causing the structure of the complex to stabilize. In addition, the effect of the compounding temperature on the interaction between modified gluten and starch significantly affects the content of slowly digestible starch. In order to save energy and reduce the adverse effects of high temperature on starch structure, 70°C is the most appropriate compounding temperature. At this temperature, the digestibility of the compound is optimal, which can effectively increase the content of slowly digestible starch.

[0039] Example 2

[0040] The other steps are the same as in Example 1, except that the method for preparing slowly digestible starch by mixing modified protein with starch is as follows:

[0041] S1: 4 g of gluten was accurately weighed and dissolved in 0.02, 0.06, 0.10, and 0.20 M malic acid solutions to prepare protein suspensions; acid treatment conditions: 70°C water bath, 200 rpm stirring, and reaction for 20 h; 2 M NaOH was used to adjust the pH to 7.0 to terminate the acid treatment; the suspension was then placed in double distilled water and dialyzed at 4°C for 48 h with a molecular weight cutoff of 3,500 Da to remove residual salt ions and small molecular impurities, and finally freeze-dried, hot-air dried, and naturally dried to constant weight to obtain acid-treated gluten;

[0042] S2: The modified gluten prepared in step 1 is mixed with potato starch at a ratio of 15% (w / w), and dissolved in double distilled water to obtain a starch-protein emulsion with a concentration of 10%; then the mixture is mixed under wet heat conditions (the wet heat treatment conditions are 70°C water bath, stirring at 200 rpm for 1 hour), and gelatinized at 95°C for 15 minutes to obtain a starch-protein complex; the complex is freeze-dried, hot-air dried and naturally dried, ground into powder and passed through a 100-mesh sieve to obtain the final products PS-MA-Glu0.02, PS-MA-Glu0.06, PS-MA-Glu0.10 and PS-MA-Glu0.2.

[0043] The evaluation method of in vitro digestion characteristics is the same as that of Example 1. The test results of the products are shown in Table 2.

[0044] Table 2: RDS, SDS and RS contents of potato starch and its starch-protein complex.

[0045]

[0046] As shown in Table 2, the rapidly digestible starch (RDS) content of PS-MA-Glu decreased significantly with the increase of malic acid concentration. This result indicates that the increase of malic acid concentration may lead to changes in gluten structure, such as unfolding and cross-linking, thereby enhancing the interaction between gluten and starch. This may promote the formation of more slowly digestible starch (SDS) and resistant starch (RS) in the complex, while reducing the content of RDS. This process may inhibit the action of enzymes on starch, thereby slowing down the digestion rate of starch. The results show that modified gluten can effectively regulate the digestion characteristics of starch, especially under high concentration malic acid (such as 0.20M), the complex exhibits stronger slow digestion characteristics. Modified gluten treated with lower concentrations of malic acid (such as 0.06M) has less effect on starch digestion, which may be because the structure of gluten is less affected at lower concentrations and fails to significantly affect its interaction with starch. In the 0.20M malic acid solution, the modification of gluten and its complexing with starch are more significant, further reducing the content of RDS and increasing the content of SDS and RS.

[0047] Example 3

[0048] The other steps are the same as in Example 1, except that the method for preparing slowly digestible starch by mixing modified protein with starch is as follows:

[0049] S1: Accurately weigh 4g of gluten, soy protein isolate, and zein, respectively, and dissolve them in 0.20M malic acid solution to prepare a protein suspension; acid treatment conditions: 70℃ water bath, 200rpm stirring, reaction for 20h; use 2M NaOH to adjust the pH to 7.0 to terminate the acid treatment; then place the suspension in double distilled water and dialyze at 4℃ for 48h. The molecular weight cutoff of the dialysis membrane is 3,500Da to remove residual salt ions and small molecular impurities, and finally freeze-dry, hot-air dry and naturally dry to constant weight to obtain acid-treated protein; the modified gluten, soy protein isolate, and zein are recorded as MA-Glu, MA-SPI, and MA-Zein, respectively;

[0050] S2: The modified protein in step 1 is mixed with potato starch at a ratio of 15% (w / w), and dissolved in double distilled water to obtain a starch-protein emulsion with a concentration of 10%; then the mixture is mixed under wet heat conditions (the wet heat treatment conditions are 70°C water bath, stirring at 200rpm for 1h), and gelatinized at 95°C for 15min to obtain a starch-protein complex; the complex is freeze-dried, hot-air dried and naturally dried, ground into powder and passed through a 100-mesh sieve to obtain the final products PS-MA-Glu, PS-MA-SPI and PS-MA-Zein.

[0051] The evaluation method of in vitro digestion characteristics is the same as that of Example 1. The test results of the products are shown in Table 3.

[0052] Table 3: RDS, SDS and RS contents of potato starch and its starch-protein complex.

[0053]

[0054] As shown in Table 3, the three modified proteins effectively regulated the digestibility of potato starch, mainly by reducing the content of rapidly digestible starch (RDS) and increasing the content of slowly digestible starch (SDS) and resistant starch (RS). Modified gluten (MA-Glu) had the most significant effect on the SDS content, while modified zein (MA-Zein) was particularly effective in increasing the RS content. These results indicate that modified proteins can improve the digestibility of starch by changing its physical structure and forming stable complexes. Therefore, selecting the appropriate type and method of use of modified proteins can effectively regulate the digestibility of starch, meet the purposes of different food processing and nutritional needs, and develop functional foods with specific digestibility characteristics.

[0055] Example 4

[0056] The other steps are the same as in Example 1, except that the method for preparing slowly digestible starch by mixing modified protein with starch is as follows:

[0057] S1: Accurately weigh 4g of gluten, soy protein isolate, and zein, respectively, and dissolve them in 0.20M citric acid solution to prepare a protein suspension; acid treatment conditions: 70℃ water bath, 200rpm stirring, reaction for 20h; use 2M NaOH to adjust the pH to 7.0 to terminate the acid treatment; then place the suspension in double distilled water and dialyze at 4℃ for 48h. The molecular weight cutoff of the dialysis membrane is 3,500Da to remove residual salt ions and small molecular impurities, and finally freeze-dry, hot-air dry and naturally dry to constant weight to obtain acid-treated protein; the modified gluten, soy protein isolate, and zein are recorded as CA-Glu, CA-SPI, and CA-Zein, respectively;

[0058] S2: The modified protein in step 1 is mixed with potato starch at a ratio of 15% (w / w), and dissolved in double distilled water to obtain a starch-protein emulsion with a concentration of 10%; then the mixture is mixed under wet heat conditions (the wet heat treatment conditions are 70°C water bath, stirring at 200 rpm for 1 hour), and gelatinized at 95°C for 15 minutes to obtain a starch-protein complex; the complex is freeze-dried, hot-air dried and naturally dried, ground into powder and passed through a 100-mesh sieve to obtain the final products PS-CA-Glu, PS-CA-SPI, and PS-CA-Zein.

[0059] The evaluation method of in vitro digestion characteristics is the same as that of Example 1. The test results of the products are shown in Table 4.

[0060] Table 4: RDS, SDS and RS contents of potato starch and its starch-protein complex.

[0061]

[0062] As shown in Table 4, different modified proteins (CA-Glu, CA-SPI, CA-Zein) significantly reduced the RDS content of potato starch and increased the SDS and RS contents. Among them, CA-Glu was most effective in increasing the SDS content, while CA-SPI and CA-Zein were more prominent in promoting the formation of resistant starch. This result shows that modified proteins can effectively regulate the digestion characteristics of starch, enhance the digestibility of starch and the formation of resistant starch. By properly selecting and adjusting the types of modified proteins, the digestion characteristics of starch can be effectively improved, thereby developing functional foods with specific digestive behaviors to meet different food functions and health needs.

[0063] In summary, the addition of modified protein has a significant effect on the structure and functional properties of potato starch, especially in increasing the content of SDS and RS. SDS and RS are two starches that are beneficial to health. Among them, SDS, with its slower digestion characteristics, helps to provide continuous and stable energy release, which is beneficial to maintaining the balance of blood sugar levels. RS, as a dietary fiber, can provide prebiotics through large intestine fermentation, improve the structure of intestinal microbial communities, and promote intestinal function. The complex prepared by the present invention has a significant increase in SDS content, which not only improves its nutritional value, provides a scientific basis for its application in health foods, but also provides potential application prospects for the development of functional foods with health benefits. For example, in diabetic diet management, the SDS in the complex can provide a smoother blood sugar response, which is of positive significance for blood sugar control in diabetic patients. In the field of medicine, the slow release characteristics of the complex make it have potential application value in drug delivery systems.

[0064] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing slowly digestible starch by mixing modified protein with starch, characterized in that: The following steps are involved: S1: preparing modified protein: dissolving the protein in double distilled water to prepare a 3-4% protein suspension; subjecting the protein to acid treatment; The pH value of all modified proteins was adjusted to 7.0, and then the suspension was placed in double distilled water and dialyzed at 0-4°C for 24-48 hours to remove residual salt ions and small molecular impurities, and then freeze-dried, hot-air dried and naturally dried to constant weight to obtain acid-treated protein; S2 Preparation of slowly digestible starch: potato starch is dissolved in double distilled water to obtain a starch emulsion with a concentration of 10%, modified protein is added to the starch emulsion at a ratio of 10-15% (w / w), treated under wet heat conditions, and then gelatinized; finally, the complex is freeze-dried, hot-air dried and naturally dried, ground into powder and passed through a 100-mesh sieve.

2. The method for preparing slowly digestible starch by mixing modified protein and starch according to claim 1, characterized in that: In the step S1, the protein is one of gluten, soy protein isolate and zein.

3. The method for preparing slowly digestible starch by mixing modified protein and starch according to claim 1, characterized in that: The acid treatment in step S1 includes: reacting in a 0.06-0.4M acid solution at 65-75°C for 16-20h.

4. The method for preparing slowly digestible starch by mixing modified protein and starch according to claim 3, characterized in that: The acidic solution is one of malic acid and citric acid.

5. The method for preparing slowly digestible starch by mixing modified protein and starch according to claim 1, characterized in that: The wet heat treatment in step S2 includes: stirring in a 40-80° C. water bath for 1-1.5 hours to promote the formation of starch-protein complexes.

6. The method for preparing slowly digestible starch by mixing modified protein and starch according to claim 1, characterized in that: The gelatinization treatment in step S2 includes: raising the water bath temperature of the starch after the wet heat treatment to 90-95° C. for gelatinization treatment, and continuing for 10-20 minutes to ensure the gelatinization of the starch.

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