Method for improving conversion efficiency of insoluble dietary fibers and soluble dietary fibers obtained by method

Abstract

The invention discloses a method for improving the conversion efficiency of insoluble dietary fibers and soluble dietary fibers obtained by the method, and belongs to the technical field of food processing and functional ingredient modification. The method comprises the following steps: performing superfine grinding treatment on wheat bran to obtain wheat bran powder; adding water into wheat bran powder, and then carrying out high-temperature and high-pressure treatment to obtain a wheat bran solution; then carrying out stepped enzymolysis on the wheat bran solution to obtain enzymatic hydrolysate; the enzymatic hydrolysate is centrifuged, lower-layer solid precipitates are insoluble dietary fibers, supernate is subjected to ethanol precipitation, and the soluble dietary fibers are obtained. The wheat bran is modified by combining superfine grinding and high-temperature and high-pressure pretreatment with stepped enzymolysis, so that the yield of the soluble dietary fibers is remarkably increased, and the functional characteristics of the soluble dietary fibers are improved. The obtained soluble dietary fiber has excellent physicochemical properties and physiological functions, and can be widely applied to baked foods, beverages, dietary supplements and other products, so that the soluble dietary fiber has important application prospects and value in the technical field of food processing.

Description

Technical Field

[0001] This invention belongs to the field of food processing and functional ingredient modification technology, specifically relating to a method for improving the conversion efficiency of insoluble dietary fiber and the soluble dietary fiber obtained by the method. Background Technology

[0002] Wheat bran is a major byproduct of wheat processing and is rich in dietary fiber, with a high proportion of insoluble dietary fiber (IDF), which limits its physiological activity and applicability in food processing. Improving the conversion rate of IDF to soluble dietary fiber (SDF) is crucial for enhancing the added value of wheat bran and expanding its application in functional foods. Existing conversion methods mostly employ single enzymatic hydrolysis or chemical treatment, which suffer from low conversion efficiency, harsh conditions, and unsatisfactory product functionality. Therefore, it is necessary to provide an efficient, mild, and industrially suitable method for converting insoluble dietary fiber to soluble dietary fiber to improve the yield and quality of soluble dietary fiber. Summary of the Invention

[0003] This invention aims to provide a highly efficient, mild, and industrially suitable method for converting insoluble dietary fiber into soluble dietary fiber. The method involves breaking down the fiber structure through ultrafine grinding and high-temperature, high-pressure pretreatment, followed by starch removal, protein removal, and a two-step enzymatic hydrolysis, significantly improving the yield and quality of soluble dietary fiber. The method described in this invention is simple to operate, allows for controllable conditions, and achieves high conversion efficiency. The resulting product possesses excellent physicochemical properties and physiological functions, and can be widely used in baked goods, beverages, and dietary supplements.

[0004] This invention provides a method for improving the conversion efficiency of insoluble dietary fiber, comprising the following steps: Wheat bran is ultra-finely pulverized to obtain wheat bran powder; water is added to the wheat bran powder, and then it is subjected to high temperature and high pressure treatment to obtain wheat bran solution; then the wheat bran solution is subjected to stepwise enzymatic hydrolysis to obtain enzymatic hydrolysate; the enzymatic hydrolysate is centrifuged, the lower solid precipitate is insoluble dietary fiber, and the supernatant is precipitated with ethanol to obtain soluble dietary fiber.

[0005] In the above method for improving the conversion efficiency of insoluble dietary fiber, the particle size of the wheat bran powder is ≥100 mesh; preferably 150 mesh.

[0006] In the above method for improving the conversion efficiency of insoluble dietary fiber, the ratio of wheat bran powder to water is 1:(5~10), g / mL; preferably 1:7, g / mL.

[0007] In the above method for improving the conversion efficiency of insoluble dietary fiber, the conditions for high temperature and high pressure treatment are: treatment at 120~140 ℃ and 0.1~0.5 MPa for 90~100 min; preferably: treatment at 135 ℃ and 0.3 MPa for 95 min.

[0008] In the above method for improving the conversion efficiency of insoluble dietary fiber, the stepwise enzymatic hydrolysis is as follows: First, α-amylase is added to the wheat bran solution for enzymatic hydrolysis to remove the starch in the wheat bran and inactivate the enzyme; then, alkaline protease is added for enzymatic hydrolysis to remove the protein in the wheat bran and inactivate the enzyme; then, cellulase and plant complex enzyme are added for segmented enzymatic hydrolysis, and after inactivation of the enzyme, an enzymatic hydrolysate is obtained.

[0009] In the above-mentioned stepwise enzymatic hydrolysis, the conditions for α-amylase hydrolysis are: adjusting the pH to 6.0, the hydrolysis temperature to 70℃, and the hydrolysis time to 40 min; the conditions for alkaline protease hydrolysis are: adjusting the pH to 11.0, the hydrolysis temperature to 50℃, and the hydrolysis time to 40 min; the conditions for segmented enzymatic hydrolysis are: adjusting the pH to 4.0, first hydrolyzing at 50℃ for 4 h, and then continuing hydrolysis at 55℃ for 4 h.

[0010] In the above-mentioned stepwise enzymatic hydrolysis, based on the mass of the wheat bran solution, the amount of α-amylase is 0.1-0.5%, the amount of alkaline protease is 0.1-0.5%, the amount of cellulase is 0.5-2%, and the amount of plant complex enzyme is 1-3%; preferably, the amount of α-amylase is 0.3%, the amount of alkaline protease is 0.3%, the amount of cellulase is 1%, and the amount of plant complex enzyme is 1.4%.

[0011] In the above method for improving the conversion efficiency of insoluble dietary fiber, the centrifugation conditions are: centrifugation at 5000~10000 rpm for 10~20 min; preferably: centrifugation at 6000 rpm for 15 min.

[0012] In the above methods for improving the conversion efficiency of insoluble dietary fiber, the volume ratio of supernatant to ethanol is 1:(1~10); preferably 1:4.

[0013] This invention provides soluble dietary fiber prepared by the above method.

[0014] The wheat bran dietary fiber powder (soluble dietary fiber) provided by this invention can be added back to baked and flour-based foods such as bread, biscuits, and noodles to effectively improve the dietary fiber content and product functional characteristics.

[0015] This invention provides the application of the above-mentioned soluble dietary fiber in improving the dietary fiber content and functional properties of pasta.

[0016] The beneficial effects of this invention are as follows: This invention utilizes a combination of ultrafine grinding and high-temperature, high-pressure pretreatment with stepwise enzymatic hydrolysis (including starch / protein removal and secondary enzymatic hydrolysis at different temperatures using cellulase and plant-based complex enzymes) to synergistically modify wheat bran. This effectively disrupts the structure of insoluble dietary fiber (IDF) and efficiently converts it into soluble dietary fiber (SDF), significantly improving the yield of soluble dietary fiber and enhancing its functional properties. The resulting product (soluble dietary fiber) possesses excellent physicochemical properties and physiological functions, and can be widely used in baked goods, beverages, and dietary supplements, thus demonstrating significant application prospects and value in the field of food processing technology. Detailed Implementation

[0017] In this invention, α-amylase and alkaline protease were purchased from Yuanye Company. Cellulase and Viscozyme were purchased from Novozymes Company. The key enzyme activity of Viscozyme is provided by endo-β-glucanase, and it also contains byproduct enzyme activities such as xylanase, cellulase, and hemicellulase. The ultrafine pulverizer is a JCWF type ultrafine pulverizer (Jinan Juncheng Machinery Company).

[0018] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0019] Example 1 The steps for preparing soluble dietary fiber from wheat bran are as follows: Wheat bran was dried at 40℃ to constant weight; then ultra-fine pulverized (≥100 mesh) using an ultra-micro pulverizer to obtain wheat bran powder; water was added at a material-to-liquid ratio of 1:7 (g / mL); the mixture was placed in an autoclave and treated under high temperature and pressure (135℃, 0.3 MPa) for 90 min to obtain a wheat bran solution; then the pH was adjusted to 6.0 with 1M HCl, and the mixture was placed in a 70℃ water bath. 0.3% α-amylase was added based on the mass of the enzymatic hydrolysis system, and the mixture was hydrolyzed for 40 min to remove starch from the wheat bran. The mixture was then removed and subjected to a boiling water bath for 10 min to inactivate the enzyme; the pH was then adjusted to 11.0 with 1M NaOH, and the mixture was placed in a 50℃ water bath. 0.3% alkaline protease was added based on the mass of the enzymatic hydrolysis system, and the mixture was hydrolyzed for 40 min to remove protein from the wheat bran. The mixture was then subjected to a boiling water bath for 10 min to inactivate the enzyme; finally, the pH was adjusted to 4.0, and 1% cellulase and 1.4% plant compound enzyme were added based on the mass of the enzymatic hydrolysis system. The mixture was hydrolyzed at 50℃ for 4 min. The enzyme was further hydrolyzed at 55℃ for 4 h (the optimal temperature for cellulase) and then at 55℃ for 4 h (the optimal temperature for plant complex enzymes). The enzyme was then inactivated by boiling in a water bath for 10 min. The resulting hydrolysate was centrifuged at 6000 rpm for 15 min, and the lower solid precipitate was collected. The precipitate was washed three times with water and then dried to obtain insoluble dietary fiber (UHE-IDF). The supernatant was added with 4 times its volume of 95% ethanol and precipitated overnight. After centrifugation, the lower precipitate was collected, dried, and soluble dietary fiber (UHE-SDF) was obtained.

[0020] Conversion rate = (M0-M1) / M0×100, where M0 represents the IDF content before conversion and M1 represents the IDF content after conversion.

[0021] The IDF content before conversion was determined by the following method: Untreated wheat bran was taken, and the initial IDF content was determined according to the method of GB 5009.88-2023, and M0 was calculated. The results showed that the insoluble dietary fiber (C-IDF) content in the untreated wheat bran was 65.08%, and the soluble dietary fiber (C-SDF) content was 6.11%.

[0022] I. Ultrafine grinding-high pressure-enzymatic response surface methodology The response surface methodology employed a Box-Behnken design, using ultrafine particle size, high-pressure time, cellulase dosage, and plant-derived complex enzyme dosage as factors, with IDF conversion rate as the response value, in a four-factor, three-level experiment. Experimental data were analyzed for variance and model fitting using Design-Expert software.

[0023] The response surface factor level table is shown in Table 1.

[0024] Table 1 Response Surface Factor Level Table The results of the response surface methodology are shown in Table 2 (Note: The IDF and SDF contents in Table 2 were measured after conversion, and the conversion rate was calculated based on the IDF mass before and after conversion. Before conversion, the IDF content of wheat bran was 65.08%).

[0025] Table 2 Results of Response Surface Experiment The analysis of variance for the model regression equation is shown in Table 3 (this analysis of variance was obtained by using Design-Expert software based on the data in Table 2).

[0026] Table 3. Analysis of variance of the model regression equation The above experimental results show that the optimal parameters for predicting the conversion rate of insoluble dietary fiber using response surface methodology are: wheat bran particle size 153.04 mesh, high pressure treatment time 95.48 min, cellulase addition amount 0.99%, plant compound enzyme addition amount 1.37%, and the model predicts a dietary fiber conversion rate of 68.22%.

[0027] To better conduct the experiment, the response surface methodology was adjusted to the following parameters: wheat bran particle size of 150 mesh, high-pressure treatment time of 95 min, cellulase addition of 1%, and plant compound enzyme addition of 1.4%. Under these parameters, insoluble dietary fiber (UHE-IDF) with a content of 20.86% and soluble dietary fiber (UHE-SDF) with a content of 25.88% were obtained, respectively. The IDF conversion rate was 67.94%, which was close to the predicted value, indicating that the regression model's prediction of dietary fiber conversion rate was accurate and reliable.

[0028] Comparative Example 1 Compared with Example 1, this comparative example did not subject the wheat bran powder to high-pressure treatment, and the remaining steps were the same as in Example 1; insoluble dietary fiber (UE-IDF) with a content of 32.42% and soluble dietary fiber (UE-SDF) with a content of 14.84% were obtained respectively; the IDF conversion rate was 50.18%.

[0029] Comparative Example 2 Compared with Example 1, this comparative example did not involve ultrafine grinding of wheat bran, but the remaining steps were the same as in Example 1; insoluble dietary fiber (HE-IDF) with a content of 34.16% and soluble dietary fiber (HE-SDF) with a content of 13.11% were obtained respectively; the IDF conversion rate was 47.51%.

[0030] Comparative Example 3 Compared with Example 1, no cellulase was added in this comparative example, and the remaining steps were the same as in Example 1; insoluble dietary fiber (UHV-IDF) with a content of 30.97% and soluble dietary fiber (UHV-SDF) with a content of 15.66% were obtained respectively; the IDF conversion rate was 52.41%.

[0031] Comparative Example 4 Compared with Example 1, no plant complex enzyme was added in this comparative example, and the remaining steps were the same as in Example 1; insoluble dietary fiber (UHC-IDF) with a content of 29.44% and soluble dietary fiber (UHC-SDF) with a content of 18.11% were obtained respectively; the IDF conversion rate was 54.76%.

[0032] Comparative Example 5 Compared with Example 1, this comparative example replaced ultrafine grinding with ultrasonic treatment (power 400 W, time 30 min), and the remaining steps were the same as in Example 1; insoluble dietary fiber (SHE-IDF) with a content of 27.18% and soluble dietary fiber (SHE-SDF) with a content of 19.95% were obtained respectively; the IDF conversion rate was 58.23%.

[0033] Comparative Example 6 Compared with Example 1, this comparative example replaced ultrafine grinding with microwave treatment (power 700 W, time 30 s), and the remaining steps were the same as in Example 1; insoluble dietary fiber (MHE-IDF) with a content of 28.02% and soluble dietary fiber (MHE-SDF) with a content of 19.03% were obtained respectively; the IDF conversion rate was 56.94%.

[0034] The above comparative examples show that omitting or replacing any key step leads to a significant reduction in conversion rate, thus proving that ultrafine grinding, high-pressure treatment, and enzymatic hydrolysis steps are crucial for improving the conversion rate of soluble dietary fiber.

[0035] Ultrafine grinding refines wheat bran particles under mechanical shearing and high-frequency collision, significantly increasing the specific surface area and exposing more active sites for dietary fiber and complex enzymes. This process partially breaks down hemicellulose, cellulose, and lignin into smaller molecules. Under prolonged high pressure at 135℃ for 95 minutes, the internal moisture of the wheat bran undergoes a continuous and uniform thermo-pressure effect, promoting deep swelling and cleavage of the lignin-cellulose-hemicellulose complex structure in the cell wall. Simultaneously, the high temperature significantly increases the solubility of insoluble macromolecules such as dietary fiber. Depressurization further tears the cell wall, exposing numerous enzyme activity sites. Subsequently, the complex enzymes synergistically and precisely cleave the insoluble macromolecules destroyed by ultrafine grinding and high-pressure pretreatment, efficiently converting them into soluble small-molecule oligosaccharides and oligosaccharides, thereby maximizing the conversion rate and functional activity of wheat bran dietary fiber.

[0036] In summary, a two-stage physical pretreatment process combining ultrafine grinding and high-pressure treatment, coupled with secondary enzymatic hydrolysis using cellulase-plant complex enzymes, significantly improves the conversion efficiency of insoluble dietary fiber to soluble dietary fiber. The conversion rate obtained by this method is similar to that of chemical methods, thus it can be considered a greener approach to improving dietary fiber conversion.

[0037] II. Testing of various dietary fiber indicators 1. Water Holding Capacity (WHC) Take 0.10 g (M1) of sample and place it in a centrifuge tube, then weigh it (M2). Add 2 g of pure water, vortex for 30 min, and then centrifuge at 8000 r / min for 10 min. Discard the supernatant. Weigh the sum of the masses of the centrifuge tube and the precipitate, and record it as M3. The calculation formula is as follows: WHC(g / g)=(M3-M2) / M1×100.

[0038] 2. Oil holding capacity (OHC) Take 0.25 g (M1) of sample and place it in a centrifuge tube, then weigh it (M2). Add 2.50 mL of soybean oil, stir quickly and evenly, then centrifuge at 8000 r / min for 10 min, discarding the supernatant. The sum of the masses of the centrifuge tube and the precipitate is recorded as M3, calculated using the following formula: OHC(g / g)=(M3-M2) / M1×100.

[0039] 3. Swelling capacity (WSC) Accurately weigh 0.5 g (M) of sample into a 10 mL graduated cylinder, shake, and read the volume of the dried sample (V2). Then add 10 mL of distilled water to the graduated cylinder, mix well, and let stand at room temperature for 4 h. Read the volume of the expanded sample (V1). The calculation formula is as follows: WSC(mL / g)=(V1-V2) / M×100.

[0040] 4. Glucose Adsorption Capacity (GAC) Add 0.8 g of dietary fiber sample to an Erlenmeyer flask, then add 50 mL of glucose standard solution (50 mmol / L) and mix well. Place the flask on a shaker at 37℃ for 6 h, then centrifuge at 4000 r / min for 15 min. Determine the glucose content in the supernatant using the DNS method and plot the glucose mass concentration standard curve y = 0.8877x + 0.007 (R²). 2 =0.9995), the calculation formula is as follows: GAC (mg / g) = (M2-M1) / M0 × 100; Where M2 is the initial total glucose content in the solution (mg), M1 is the glucose content measured in the supernatant (mg), and M0 is the dry weight of the sample (g).

[0041] The test results are shown in Table 4.

[0042] Table 4. Functional characteristics of different SDFs As shown in Table 4, the water-holding capacity (8.91 g / g) and oil-holding capacity (16.83 g / g) of UHE-SDF were significantly higher than those of other groups. This is because the synergistic effect of ultrafine grinding-high pressure-dual enzyme treatment disrupted the crystalline regions of the fiber, forming a hierarchical porous structure. This structure enhances hydration through exposed hydrophilic groups such as hydroxyl and carboxyl groups, and improves oil retention capacity through increased specific surface area (physical adsorption) and hydrophobic interface (van der Waals forces). In contrast, the untreated (wheat bran) C-SDF had the lowest water-holding capacity (2.20 g / g) and oil-holding capacity (5.07 g / g), indicating that its dense structure lacks effective adsorption sites. The limited effectiveness of single-enzyme treatments on UHV-SDF (oil holding capacity 6.83 g / g) and UHC-SDF (oil holding capacity 7.67 g / g) further underscores the necessity of dual-enzyme synergy in constructing a dual adsorption interface. Furthermore, physical modification of the SDF's three-dimensional structure, increasing the amount of short-chain dietary fiber, may have induced a porous and rough surface in the dietary fiber, promoting oil absorption. The swelling capacity of UHE-SDF (2.67 mL / g) was significantly superior to other groups. This is because the increased porosity and surface area after modification improved the contact between dietary fiber and water, contributing to the increased swelling capacity. The increased porosity and surface area after both physical and enzymatic modifications improved the contact between dietary fiber and water, thus contributing to the increased swelling capacity.

[0043] The glucose adsorption capacity of UHE-SDF (76.22 mg / g) significantly exceeded that of other groups, approximately twice that of C-SDF. This is likely due to the increased porous structure and specific surface area resulting from the combined modification process, which facilitates glucose embedding within the fiber network. Consequently, its glucose adsorption capacity is enhanced. This reflects the synergistic effect of its "triple adsorption mechanism": the porous structure provides physical retention sites, the soluble fibers form a gel network to delay glucose diffusion, and cellulase treatment enhances hydrogen bonding by exposing hydroxyl groups. Notably, UHV-SDF (52.31 mg / g) and UHC-SDF (61.11 mg / g) treated with only a single enzyme exhibited relatively low adsorption capacities, demonstrating the crucial importance of dual-enzyme synergy for sufficient exposure of active sites. This multi-mechanism interaction enables the modified dietary fiber to exhibit superior glucose adsorption performance, providing a theoretical basis for its application in regulating postprandial blood glucose.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for improving the conversion efficiency of insoluble dietary fiber, characterized by, The steps are as follows: The wheat bran is subjected to ultrafine pulverization to obtain wheat bran powder; water is added to the wheat bran powder, which is then subjected to high-temperature and high-pressure treatment to obtain a wheat bran solution; the wheat bran solution is subjected to stepwise enzymatic hydrolysis to obtain an enzymatic hydrolysate; the enzymatic hydrolysate is centrifuged, and the lower solid precipitate is insoluble dietary fiber, and the supernatant is precipitated with ethanol to obtain soluble dietary fiber.

2. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 1, characterized by, The particle size of the wheat bran powder is greater than or equal to 100 mesh.

3. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 1, wherein The ratio of the wheat bran powder to water is 1: (5-10) g / mL.

4. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 1, wherein The high-temperature and high-pressure treatment is performed at 120-140 ℃ and 0.1-0.5 MPa for 90-100 min.

5. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 1, wherein The stepwise enzymatic hydrolysis is as follows: first, α-amylase is added to the wheat bran solution for enzymatic hydrolysis to remove starch in the wheat bran, and the enzyme is inactivated; then, alkaline protease is added for enzymatic hydrolysis to remove protein in the wheat bran, and the enzyme is inactivated; then, cellulase and plant complex enzyme are added for stepwise enzymatic hydrolysis, and the enzymes are inactivated to obtain the enzymatic hydrolysate.

6. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 5, wherein The conditions for the α-amylase enzymatic hydrolysis are as follows: the pH is adjusted to 6.0, the enzymatic hydrolysis temperature is 70 ℃, and the enzymatic hydrolysis time is 40 min; the conditions for the alkaline protease enzymatic hydrolysis are as follows: the pH is adjusted to 11.0, the enzymatic hydrolysis temperature is 50 ℃, and the enzymatic hydrolysis time is 40 min; and the conditions for the stepwise enzymatic hydrolysis are as follows: the pH is adjusted to 4.0, the enzymatic hydrolysis is first performed at 50 ℃ for 4 h, and then the enzymatic hydrolysis is continued at 55 ℃ for 4 h.

7. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 5, wherein The amount of the α-amylase is 0.1-0.5% based on the mass of the wheat bran solution, the amount of the alkaline protease is 0.1-0.5%, the amount of the cellulase is 0.5-2%, and the amount of the plant complex enzyme is 1-3%.

8. The method of improving the conversion efficiency of insoluble dietary fiber according to claim 1, wherein The volume ratio of the supernatant to ethanol is 1: (1-10).

9. The soluble dietary fiber prepared by the method of any one of claims 1-8.

10. The use of the soluble dietary fiber of claim 9 in improving the dietary fiber content and functional properties of flour.

Images