A method for inhibiting the digestibility of high-temperature gelatinized rice starch

Abstract

This invention discloses a method for inhibiting the digestibility of rice starch gelatinized at high temperatures, comprising the following steps: subjecting soybean protein sequentially to ultrasonication, enzymatic hydrolysis, and acid-heat treatment to form heat-resistant and acid-resistant high aspect ratio rigid soybean protein fibers; mixing the obtained soybean protein fibers with a rice starch suspension, followed by gelatinization treatment to obtain a soybean protein fiber-rice starch complex. This invention, by constructing structurally stable soybean protein fibers, enables them to form a dense complex with rice starch during starch gelatinization and subsequent digestion, effectively inhibiting the digestibility of rice starch by α-amylase. The slow-digesting starch content reaches 20.48%~23.42%, and the resistant starch content reaches 30.11%~31.76%, approximately five times higher than that of natural rice starch. This invention requires no chemical cross-linking agents, and the process is green, safe, and controllable, suitable for the industrial production of low glycemic index foods.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a method for inhibiting the digestibility of rice starch gelatinized at high temperatures, and more particularly to a processing method for preparing soybean protein fiber by ultrasound-assisted enzymatic hydrolysis and compounding it with rice starch to increase the content of resistant starch. Background Technology

[0002] Rice starch is one of the most consumed grain starches globally, boasting advantages such as fine granules, mild taste, and low allergenicity, making it widely used in traditional staple foods like infant formula, puffed foods, rice noodles, and rice vermicelli. However, natural rice starch is characterized by rapid digestion and a high glycemic index (GI). Its starch components are quickly broken down into glucose by enzymes in the small intestine, leading to a rapid rise in postprandial blood sugar. Long-term consumption of high-GI foods is closely related to the development of metabolic diseases such as diabetes, obesity, and cardiovascular disease. Therefore, developing rice starch products with low digestibility is of great significance for improving public nutritional health.

[0003] Existing technologies for inhibiting starch digestibility mainly fall into three categories: physical modification, chemical modification, and enzymatic modification. Physical modifications, such as wet heat treatment, pressure heat treatment, and microwave treatment, reduce enzymatic sensitivity by altering the crystalline structure and particle morphology of starch. Chemical modifications, such as cross-linking and esterification, introduce chemical groups to hinder the binding of enzymes to starch molecules. Enzymatic modification utilizes branching enzymes or transglucosidases to change the chain length distribution of starch. In addition, adding exogenous components (such as dietary fiber, protein, lipids, or polyphenols) to starch has also been proven to effectively inhibit the rate of starch digestion.

[0004] Soy protein, as a high-quality plant protein, has been widely used in recent years for lowering the glycemic index (GI) of starchy foods. Existing research shows that soy protein and its hydrolysates can inhibit α-amylase activity or reduce enzyme accessibility to starch by forming hydrogen bonds, electrostatic interactions, or physical encapsulation with starch molecules, thereby delaying starch digestion. However, the interaction between natural protein and starch is relatively weak, resulting in limited digestive inhibition, and often requires the addition of large amounts of protein to achieve the desired effect, affecting the product's taste and texture. Furthermore, conventional protein-starch complex methods typically ignore the destructive effect of the acidic environment of the stomach on protein structure, making it difficult for the protein to maintain its intact structure after entering the gastrointestinal tract, thus weakening its effect in inhibiting starch digestion.

[0005] Therefore, developing a simple process that does not require chemical cross-linking agents and can effectively inhibit the digestibility of rice starch, especially a technical solution that constructs acid-heat resistant soybean protein fiber and forms a stable complex with rice starch, has significant practical application value and market prospects. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention provides a simple method for inhibiting the digestibility of high-temperature gelatinized rice starch without the addition of chemical cross-linking agents. This invention modifies and reshapes the fibrous structure of soybean protein through steps such as ultrasound, enzymatic hydrolysis, and acid-heat treatment, thereby enhancing its structural stability during starch gelatinization and digestion.

[0007] The purpose of this invention is to provide a method for inhibiting the digestibility of rice starch gelatinized at high temperatures, comprising the following steps: (1) Preparation of soybean protein fiber: Soybean protein is dispersed in water and subjected to ultrasonic treatment, enzymatic hydrolysis and acid heat treatment in sequence to obtain soybean protein fiber; (2) Preparation of rice starch complex: The soybean protein fiber obtained in step (1) is mixed with rice starch suspension and gelatinized to obtain soybean protein fiber-rice starch complex.

[0008] In one embodiment of the present invention, in step (1), the protein content of soybean protein is 90.05%~90.29% (w / w, dry basis).

[0009] In one embodiment of the present invention, in step (1), soybean protein is suspended in ultrapure water at a concentration of 9.8~10.0 mg / mL and stirred continuously at 380~400 r / min for 700~720 min; the conditions for ultrasonic treatment are: ultrasonic frequency 25kHz, power 380~400 W, treatment time 280~360 s, pulse interval 2 seconds, and the reaction vessel is placed in an ice-water bath throughout the process to prevent the accumulation of acoustic heat.

[0010] In one embodiment of the present invention, in step (1), the conditions for enzymatic hydrolysis are as follows: the pH value of the ultrasonically treated soybean protein dispersion is adjusted to 8.0, trypsin (enzyme activity of 250 U / mg) is added at an enzyme to substrate mass ratio of 1:100, and the mixture is incubated at a constant temperature of 35~37℃ and 180~200 r / min for 28~35 min, and then the enzymatically hydrolyzed solution is heated at 93~95℃ for 13~15 min to inactivate the enzyme.

[0011] In one embodiment of the present invention, in step (1), the conditions for acid heat treatment are as follows: the pH value of the dispersion after enzyme inactivation treatment is adjusted to 2.0, and the mixture is heated in a water bath at 88~90℃ and 180~200 r / min for 460~480 min with stirring. After the heating is completed, the mixture is immediately transferred to an ice-water bath to terminate the reaction.

[0012] In one embodiment of the present invention, in step (2), the concentration of rice starch suspension is 1.96~2.00 g / L, the amount of soybean protein fiber added is 25% of the mass of rice starch, and the pH value is adjusted to 7.0 after the two are mixed.

[0013] In one embodiment of the present invention, in step (2), the gelatinization treatment conditions are as follows: the soybean protein fiber-rice starch mixture is heated in a water bath at 98~100℃ for 18~20 min, and then immediately cooled to 35~37℃.

[0014] In one embodiment of the present invention, the soybean protein fiber-rice starch complex contains 20.48% to 23.42% slow-digestible starch (SDS) and 30.11% to 31.76% resistant starch (RS).

[0015] This invention provides a method for preparing soybean protein fiber by ultrasound-assisted enzymatic hydrolysis and then compounding it with rice starch to inhibit its digestibility. First, the soybean protein solution is pretreated with ultrasound to disrupt the non-covalent bonds of protein molecules through cavitation, causing the structure to partially unfold and exposing more enzyme cleavage sites. Then, trypsin is added for restriction hydrolysis, generating short peptide fragments with uniform molecular weight distribution. Next, the solution is continuously heated under strong acid (pH 2.0) and high temperature (approximately 90°C) conditions to induce these peptide fragments to self-assemble through β-sheet structures, forming starch-like soybean protein fibers with high heat and acid resistance. When this fiber is mixed with rice starch suspension and gelatinized, the protein fiber binds tightly to the dissolved starch molecules through hydrogen bonds, electrostatic interactions, and physical entanglement, forming a dense protein fiber-starch network structure. This structure forms a physical barrier layer on the surface of starch granules, effectively blocking the accessibility of α-amylase to the starch substrate. Simultaneously, because the protein fiber itself maintains its intact morphology under the high temperature of gelatinization and the subsequent acidic environment of the stomach, it continuously inhibits the enzymatic hydrolysis rate of starch, ultimately achieving a significant increase in the content of slow-digesting starch and resistant starch.

[0016] Compared with the prior art, the present invention has the following significant advantages: (1) Significantly inhibits the digestibility of high-temperature gelatinized rice starch and increases the content of resistant starch: The rice starch complex treated by the method of this invention exhibits significantly improved in vitro digestibility. Testing revealed that the slow-digestible starch (SDS) content in the product reached 20.48%~23.42%, and the resistant starch (RS) content reached 30.11%~31.76%, with a combined content exceeding 50%. Compared to natural rice starch (RS approximately 5%), the RS content of the rice starch complex of this invention is increased by approximately 5 times, making it suitable for developing low glycemic index (GI) foods.

[0017] (2) No chemical cross-linking agents required, high safety: This invention does not add any chemical cross-linking agents (such as epichlorohydrin, sodium trimetaphosphate, etc.) throughout the entire process. It achieves protein fiberization and compounding with starch only through a green combination process of physical (ultrasound), enzymatic (trypsin) and acid heat treatment. The final product has no risk of chemical reagent residue, which is in line with the development trend of clean label and natural food ingredients.

[0018] (3) The process conditions are mild and controllable, suitable for industrial production: The ultrasonic, enzymatic hydrolysis, acid-heat stirring and conventional gelatinization processes used in this invention are all based on an aqueous system, without involving high pressure or organic solvents. The operating parameters are clear and easy to scale up on conventional food processing equipment. At the same time, soybean protein is widely available and inexpensive, and the overall production cost is controllable, showing good prospects for industrial application. Attached Figure Description

[0019] Figure 1 The images show the microstructure of soybean protein fibers prepared in Comparative Examples 2-4 and Example 3 of this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] The rice starch and soybean protein raw materials used in the embodiments of the present invention are obtained through conventional commercial channels.

[0022] 1) The average particle size of the soybean protein fiber prepared by this invention was determined according to the following method.

[0023] A soybean protein fiber suspension with a concentration of 1.0 mg / mL was prepared using a 0.005 mol / L phosphate buffer solution at pH 7.0, and its average particle size was measured using a nanoparticle size analyzer at 25°C.

[0024] 2) The digestibility of the rice starch complex prepared in this invention was tested according to the following method.

[0025] The pH of the soybean protein fiber-rice starch complex was adjusted to 1.5, and 9 mL of 25 mg / mL pepsin (675,000 U) was added. The mixture was digested in a shaker at 37°C for 1 h, followed by inactivation at 100°C for 15 min. After cooling to room temperature and adjusting the pH to 6.9, a mixture of α-amylase (200 U) and amyloglucosidase (500 U) was added at a 1:5 ratio. 1 mL samples were taken at 0, 20, 50, 70, 90, 120, 150, and 180 min of the reaction mixture. The collected reaction solution was inactivated by high-temperature inactivation, cooled, and centrifuged at 10,000 r / min for 5 min. The glucose release content was determined using the DNS method.

[0026] Total starch hydrolysis is expressed as the percentage of starch hydrolyzed at different times, and is calculated as follows: Total starch hydrolysis (%) =

[0027] Glucose was converted into starch by multiplying the weight of the released glucose by 0.9. The starch digestion behavior of the samples was then analyzed based on the following equation.

[0028] C t =C ∞ (1 e kt ) Among them, C t C is the percentage of starch digested at time t (min). ∞ It is the estimated percentage of starch digested at the end of digestion, and k is the first-order rate constant.

[0029] The levels of RDS (rapidly digestible starch), SDS (slowly digestible starch), and RS (resistant starch) are also calculated using the following formulas: RDS (%) = G 20 × 0.9 × 100 SDS (%) = (G 120 G 20 ) × 0.9 × 100 RS (%) = (1 RDS – SDS) × 100.

[0030] Example 1 A method for inhibiting the digestibility of rice starch gelatinized at high temperatures, specifically including the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.05%) was suspended in ultrapure water at a concentration of 9.8 mg / mL and stirred continuously at 380 r / min for 700 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 380 W for 280 seconds with a pulse interval of 2 seconds. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 35℃ and 180r / min for 28min with constant stirring. Then heat the enzyme hydrolysate at 93℃ for 13min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 88℃ and 180r / min for 460min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0031] (2) Preparation of rice starch complex: Soy protein fiber (0.0098g) was added to 20 mL of rice starch suspension (1.96g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 98℃ for 18 min and then immediately cooled to 35℃ to obtain a soybean protein fiber-rice starch complex.

[0032] Example 2 A method for inhibiting the digestibility of rice starch gelatinized at high temperatures, specifically including the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.11%) was suspended in ultrapure water at a concentration of 9.9 mg / mL and stirred continuously at 390 r / min for 710 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 390 W for 290 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 36℃ and 190 r / min for 29 min with constant stirring. Then heat the enzyme hydrolysate at 94℃ for 14 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 89℃ and 190 r / min for 470 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0033] (2) Preparation of rice starch complex: Soy protein fiber (0.0099 g) was added to 20 mL of rice starch suspension (1.98 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a 99℃ water bath for 19 min and immediately cooled to 36℃ to obtain a soybean protein fiber-rice starch complex.

[0034] Example 3 A method for inhibiting the digestibility of rice starch gelatinized at high temperatures, specifically including the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 300 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 30 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0035] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0036] Example 4 A method for inhibiting the digestibility of rice starch gelatinized at high temperatures, specifically including the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 360 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 30 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0037] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0038] Example 5 A method for inhibiting the digestibility of rice starch gelatinized at high temperatures, specifically including the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 300 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 35 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0039] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0040] The average particle size of soybean protein fiber and the digestibility of rice starch complex in the examples were tested and are shown in Table 1. Table 1

[0041] As shown in Table 1, the slow-digestible starch content in the soybean protein fiber-rice starch complex reaches over 20%, and the resistant starch content reaches over 30%, totaling over 50%. Compared to natural rice starch (approximately 5% resistant starch), the resistant starch content of this invention is increased by approximately 5 times.

[0042] Comparative Example 1 Referring to Example 3, the soybean protein fiber in the rice starch mixture was replaced with soybean protein. Specifically, the following steps were taken: 0.010 g of soybean protein was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein-rice starch mixture was then heated in a water bath at 100°C for 20 min and then immediately cooled to 37°C to obtain a soybean protein-rice starch complex.

[0043] The average particle size of soybean protein and the digestibility of rice starch complex in Comparative Example 1 were tested and are shown in Table 2. Table 2

[0044] The comparative analysis of the data in Tables 1 and 2 shows that, compared with rice starch without added soy protein, the resistant starch content of the rice starch complex with added soy protein increased by only 2.23%, which is much lower than the resistant starch content in Example 3 (30.88%). This indicates that the effect of soy protein fiber in inhibiting the digestibility of high-temperature gelatinized rice starch is significantly better than that of soy protein.

[0045] Comparative Example 2 Referring to Example 3, the preparation process of soybean protein fiber does not include ultrasonic treatment and enzymatic hydrolysis, while other conditions remain unchanged. Specifically, it includes the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The pH of the dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0046] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0047] Comparative Example 3 Referring to Example 3, the preparation process of soybean protein fiber does not include ultrasonic treatment, while other conditions remain unchanged. Specifically, it includes the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 30 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0048] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0049] Comparative Example 4 Referring to Example 3, the preparation process of soybean protein fiber does not include enzymatic hydrolysis, while other conditions remain unchanged. Specifically, it includes the following steps: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 300 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. After adjusting the pH of the ultrasonically treated dispersion to 2.0, the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0050] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0051] The microstructures of soybean protein fibers prepared in Comparative Examples 2-4 and Example 3 are as follows: Figure 1 As shown.

[0052] The digestibility of the rice starch complex in Comparative Examples 2-4 was compared, as shown in Table 3. Table 3

[0053] Depend on Figure 1 As shown in Table 3, the preparation process of soybean protein fiber is crucial, with significant differences in the structural morphology and size distribution of soybean protein fibers obtained through different processes. Further comparative analysis with Table 1 reveals that only through the synergistic effect of ultrasound, enzymatic hydrolysis, and acid heating can soybean protein fibers with a high aspect ratio and strong rigidity be formed. Figure 1 In Example 3), the soybean protein fiber-rice starch complex with the best inhibitory effect on the digestibility of rice starch can be prepared.

[0054] Comparative Example 5 Referring to Example 3, only the pH value of the acid heat treatment during the preparation of soybean protein fiber was adjusted to neutral, while other conditions remained unchanged. Specifically, the following steps were included: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 300 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 30 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 7.0, and the mixture was heated in a water bath at 90℃ and 200 r / min for 480 min with stirring. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0055] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0056] Table 4 shows the average particle size of soybean protein fiber and the digestibility of rice starch complex in Comparative Example 5: Table 4

[0057] As shown in Table 4, the average particle size of soybean protein fibers in Comparative Example 5 was significantly smaller than that in all examples, and even smaller than the average particle size of soybean protein. This indicates that the soybean protein hydrolysate treated with ultrasound-assisted enzymatic hydrolysis cannot form soybean protein fibers with a high aspect ratio under neutral conditions; they can only be formed under acidic conditions and heating. Further analysis of the digestibility of the rice mixtures in Tables 1 and 4 revealed that the soybean protein hydrolysate that did not form protein fibers had almost no effect on inhibiting the digestibility of high-temperature gelatinized rice starch.

[0058] Comparative Example 6 Referring to Example 3, only the temperature of the acid heat treatment during the preparation of soybean protein fiber was adjusted (50°C, 60°C, 70°C), while other conditions remained unchanged. Specifically, the following steps were included: (1) Preparation of soybean protein fiber: Soy protein (dry basis protein content of 90.29%) was suspended in ultrapure water at a concentration of 10.0 mg / mL and stirred continuously at 400 r / min for 720 min to ensure full hydration. The soybean protein dispersion was treated with an ultrasonic cell disruptor at a frequency of 25 kHz and a power of 400 W for 300 s with a pulse interval of 2 s. To avoid the heat generated by the ultrasound, the reaction vessel was placed in an ice-water bath throughout the process. Adjust the pH of the soybean protein dispersion to 8.0, add trypsin (enzyme activity 250 U / mg) at an enzyme to substrate mass ratio of 1:100, and incubate at 37℃ and 200 r / min for 30 min with constant stirring. Then heat the enzyme hydrolysate at 95℃ for 15 min to inactivate the enzyme. The pH of the enzyme-inactivated dispersion was adjusted to 2.0, and the mixture was heated in a water bath at different temperatures (50℃, 60℃, 70℃) at 200 rpm for 480 min. After heating, the mixture was immediately transferred to an ice-water bath to terminate the reaction, thus obtaining soybean protein fiber.

[0059] (2) Preparation of rice starch complex: Soy protein fiber (0.010 g) was added to 20 mL of rice starch suspension (2.00 g / L). After mixing, the pH value was adjusted to 7.0. The soybean protein fiber-rice starch mixture was then heated in a water bath at 100℃ for 20 min and then immediately cooled to 37℃ to obtain a soybean protein fiber-rice starch complex.

[0060] Table 5 shows the average particle size of soybean protein fiber and the digestibility of rice starch complex in Comparative Example 6: Table 5

[0061] As shown in Table 5, the average particle size of soybean protein fibers in Comparative Example 6 was significantly smaller than that in the other examples, and similar to the average particle size of soybean protein. This indicates that the acid heat treatment temperature is also an important factor affecting the formation of soybean protein fibers; only acid heat treatment at high temperatures can form soybean protein fibers with a high aspect ratio. Further analysis of the digestibility of rice starch complexes in Tables 1 and 5 also revealed that only high aspect ratio protein fibers with a relatively large average particle size (above 1000 nm) have the effect of inhibiting the digestibility of high-temperature gelatinized rice starch.

[0062] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method of inhibiting the digestibility of high-temperature gelatinized rice starch, characterized by, Includes the following steps: (1) Preparation of soybean protein fiber: Soybean protein is dispersed in water and subjected to ultrasonic treatment, enzymatic hydrolysis and acid heat treatment in sequence to obtain soybean protein fiber; (2) Preparation of rice starch complex: The soybean protein fiber obtained in step (1) is mixed with rice starch suspension and gelatinized to obtain soybean protein fiber-rice starch complex.

2. The method of claim 1, wherein, In step (1), the protein content of the soybean protein is 90.05%~90.29%.

3. The method of claim 1, wherein, In step (1), soybean protein is suspended in ultrapure water at a concentration of 9.8~10.0 mg / mL and stirred continuously at 380~400 r / min for 700~720 min; the subsequent ultrasonic treatment conditions are: ultrasonic frequency 25 kHz, power 380~400 W, treatment time 280~360 s, pulse interval 2 seconds, and the reaction vessel is placed in an ice-water bath throughout the process.

4. The method of claim 1, wherein, In step (1), the conditions for enzymatic hydrolysis are as follows: the pH of the ultrasonically treated soybean protein dispersion is adjusted to 8.0, trypsin is added at an enzyme-to-substrate mass ratio of 1:100, the enzyme activity of trypsin is 250 U / mg, and the mixture is incubated at 35~37℃ and 180~200 r / min for 28~35 min with constant temperature stirring, and then the hydrolyzed solution is heated at 93~95℃ for 13~15 min to inactivate the enzyme.

5. The method of claim 1, wherein, In step (1), the acid heat treatment conditions are as follows: adjust the pH of the enzyme-inactivated dispersion to 2.0, heat it in a water bath at 88~90℃ and 180~200 r / min for 460~480 min, and immediately transfer it to an ice-water bath to terminate the reaction after heating.

6. The method of claim 1, wherein, In step (2), the concentration of rice starch suspension is 1.96~2.00 g / L, the amount of soybean protein fiber added is 25% of the mass of rice starch, and the pH value is adjusted to 7.0 after the two are mixed.

7. The method according to claim 1, characterized in that, In step (2), the gelatinization conditions are as follows: the soybean protein fiber-rice starch mixture is heated in a water bath at 98~100℃ for 18~20 min, and then immediately cooled to 35~37℃.

8. The method according to claim 1, characterized in that, In the soybean protein fiber-rice starch complex, the slow-digestible starch content reaches 20.48%~23.42%, and the resistant starch content reaches 30.11%~31.76%.

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