Soluble dietary fiber from bean dregs as well as preparation method and application of soluble dietary fiber

Abstract

The invention discloses a bean dreg soluble dietary fiber preparation method, which comprises: 1, adding bean dregs into a phosphate buffer solution, and shaking to obtain pretreated bean dregs; step 2, adding nutrient substances into the pretreated bean dregs obtained in the step 1, uniformly mixing to obtain a fermentation culture medium, and inoculating penicillium expansum into the fermentation culture medium for fermentation treatment to obtain fermented bean dregs; and step 3, carrying out solid-liquid separation on the fermented bean dregs obtained in the step 2, collecting clear liquid, concentrating to obtain concentrated liquid, carrying out alcohol precipitation, collecting precipitates, and drying to obtain the bean dreg soluble dietary fibers. The preparation method disclosed by the invention is simple and short in period, and the content of soluble dietary fibers in the bean dregs in the prepared product is as high as 51.5%; the bean dreg soluble dietary fiber prepared by the method disclosed by the invention is looser and more porous in structure, the solubility is remarkably improved, and the bean dreg soluble dietary fiber has a remarkable effect in promoting the growth of intestinal beneficial flora and has a relatively good application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of food biotechnology, and particularly relates to a bean dreg soluble dietary fiber as well as a preparation method and application thereof. BACKGROUND

[0002] Bean dregs are by-products of the bean product manufacturing industry, and contain rich dietary fiber, protein, lipids, isoflavones and various inorganic salts, and have high nutritional value. China is the world's major soybean producing and consuming country, and the annual domestic bean product industry produces more than 20 million tons of bean dregs. At present, bean dregs are mainly used in animal feed additives and fertilizer fields, and most of them are still at the laboratory level in the development of flavor beverages, baked foods and edible fungus fermentation to produce bioactive substances, and most of them are treated as waste, which causes environmental pollution and resource waste. Therefore, the resourceization and high-value utilization of bean dregs are research hotspots in the field of food processing at home and abroad.

[0003] Dietary fiber accounts for more than 50% of bean dregs, and is an excellent functional food raw material in promoting gastrointestinal peristalsis, reducing sugar and fat, preventing cardiovascular and cerebrovascular diseases, etc. Dietary fiber is divided into insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) according to whether it is soluble in water, among which SDF has smaller molecular weight, more loose structure, more active factors, better adsorption capacity, antioxidant activity and immune regulation activity than IDF, and has higher gel forming capacity and stronger emulsifying capacity, and has greater development prospects in the development and utilization of food, medicine and other fields. However, there are problems in the practical application of bean dregs, such as high water content, difficulty in preservation, significant beany taste, poor palatability, many harmful health resistance factors, and low SDF content (less than 5%).

[0004] The existing reported preparation methods of SDF mainly include chemical method, physical method, biological method and combined method. Chen et al. used explosion extrusion technology to increase the SDF content of bean dregs from 2.6% to 30.1%, and also improved the physicochemical properties of SDF, and Wang Jinan et al. used microwave technology to treat bean dregs, and increased the SDF content from 4.60% to 11.43%. The equipment required by the physical method is relatively expensive, and the control requirements of the treatment conditions are high, which is easy to cause over-treatment and cause loss of SDF. Yoshida et al. used hydrogen peroxide to treat bean dregs, and under the optimal conditions (2% H2O2, 42℃, 5 h), the SDF content was increased by 6 times. Although the chemical method has the advantages of simple operation and short extraction time, the reagents used have certain corrosion to the equipment, are easy to pollute the environment, and also have certain damage to SDF, resulting in partial loss of SDF.

[0005] Biochemical method mainly refers to enzyme method and fermentation method. Li Reng et al. used cellulase to extract SDF from black beans, and under the optimal extraction process (solid-liquid ratio 1:25 (g / mL), enzyme addition amount 2.2%, enzymolysis temperature 45℃, enzymolysis time 7 h, and enzymolysis pH 5.0), the extraction rate of SDF in black beans reached 38.40%. Due to the strong specificity of enzymes, and the complex composition and structure of agricultural and sideline products, multiple enzymes often need to be combined for application, and the price of enzymes is relatively high, which limits the industrial application. Fermentation method is to use cellulase, hemicellulase, protease and other enzymes produced by microbial fermentation and metabolically produced organic acids to degrade macromolecular IDF under the dual action of the enzymes, so as to improve the content of soluble polysaccharide. The commonly used microorganisms for fermented bean dregs are molds, such as Aspergillus oryzae, Aspergillus niger and Trichoderma viride. Zhang Yu used Mucor combined with lactic acid bacteria to ferment bean dregs to prepare SDF, and under the optimal conditions, the content of SDF reached 34.27%, which was 8.5 times the content of fresh bean dregs.

[0006] Combined extraction method is a method of combining two or more extraction methods to extract SDF. For example, patent CN117941804A discloses a strong ultraviolet modification of bean dregs, and a brewing yeast and lactobacillus combined fermentation modification technology. After the modified bean dregs are subjected to enzymolysis by alpha-amylase, protease and glucoamylase, the extraction rate of SDF reaches 21.81%. In patent CN116420846A, the bean dregs are subjected to ball milling treatment and then subjected to enzymolysis by cellulase to obtain modified bean dregs, and a soft candy suitable for diabetics is prepared, wherein the extraction rate of SDF is 6.97%. Patent CN119924456A discloses a method for preparing soluble dietary fiber from bean dregs by using Aspergillus oryzae two-stage pretreatment, and the total fermentation period is as long as 150 hours. Through literature analysis, it can be known that certain progress has been made in the preparation and application of soluble fiber from bean dregs, but the current methods still have problems such as long operation period, high cost and low yield. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a preparation method of soluble dietary fiber from bean dregs.

[0008] The technical problem to be solved by the present application is to provide a preparation method of soluble dietary fiber from bean dregs.

[0009] The technical problem to be solved by the present application is to provide a preparation method of soluble dietary fiber from bean dregs.

[0010] In order to solve the above technical problems, the technical solutions provided by the present application are as follows:

[0011] A preparation method of soluble dietary fiber from bean dregs, comprising the following steps:

[0012] Step 1: Add soybean residue to phosphate buffer solution, shake, and obtain pretreated soybean residue;

[0013] Step 2: Add nutrients to the pretreated soybean residue obtained in Step 1, mix well, and prepare a fermentation culture medium. Inoculate Penicillium expansum into the fermentation culture medium for fermentation treatment to obtain fermented soybean residue.

[0014] Step 3: Separate the fermented soybean residue obtained in Step 2 into solid and liquid components, collect the clear liquid, concentrate it to obtain a concentrated liquid, precipitate it with alcohol, collect the precipitate, and dry it to obtain soluble dietary fiber from soybean residue.

[0015] In step 1, the soybean residue is wet soybean residue.

[0016] In step 1, the phosphate buffer is any one of citrate-disodium hydrogen phosphate buffer (CP), sodium dihydrogen phosphate-disodium hydrogen phosphate buffer (PN), and potassium dihydrogen phosphate-disodium hydrogen phosphate buffer (PK); the concentration of the phosphate buffer is 0.01 ~ 0.5 mol / L, and the pH is 5.5 ~ 6.5.

[0017] Preferably, the phosphate buffer is a 0.05 M citrate-disodium hydrogen phosphate buffer with a pH of 5.5.

[0018] In step 1, the amount of soybean residue added is 100-250 g per liter of phosphate buffer, preferably 200 g per liter of phosphate buffer; the pretreatment is a shaking treatment for 1-4 hours.

[0019] In step 2, the nutrients include sucrose and urea; the amount of sucrose added is 5-10 g per liter of pretreated soybean residue; the amount of urea added is 0.1-0.5 g per liter of pretreated soybean residue; the pH of the fermentation medium is 6.0-7.0, preferably 6.5.

[0020] In step 2, the inoculation method for *Penicillium expansum* is as follows: *Penicillium expansum* spore suspension is inoculated into the seed culture medium at an inoculation rate of 1-10% v / v, and cultured at 25-32℃ and 150-220 r / min for 18-36 h to obtain the seed culture. This seed culture is then inoculated into the fermentation medium at an inoculation rate of 5-15% v / v. The concentration of the *Penicillium expansum* spore suspension is 10... 5 ~ 10 7 per mL.

[0021] Preferably, the seed culture medium comprises the following components: 4.0 ~ 10.0 g / L glucose, 5.0 ~ 20.0 g / L corn steep liquor powder; the pH of the seed culture medium is 6.0 ~ 7.0.

[0022] Preferably, the seed culture is inoculated into the fermentation medium at an inoculation rate of 8% to 10% v / v.

[0023] Most preferably, the seed culture is inoculated into the fermentation medium at an inoculation rate of 10% v / v.

[0024] In step 2, the fermentation conditions are: temperature 25 ~ 32 ℃, pH 6.0 ~ 7.0, rotation speed 150 ~ 220 r / min, and fermentation time 24 ~ 48 h.

[0025] Preferably, the fermentation time is 24 to 30 hours.

[0026] Most preferably, the fermentation time is 30 h.

[0027] Preferably, in step 2, the fermentation medium is sterilized by high temperature and high pressure and then cooled before being inoculated with Penicillium expansum.

[0028] In step 2, the extended Penicillium is a strain Penicillium expansum CGMCC 3.15402.

[0029] In step 3, the solid-liquid separation is centrifugation at 4000-6000 r / min for 10-20 min; the concentration is vacuum concentration at 50-60℃ to 20-50% of the initial volume.

[0030] Preferably, the concentration is performed by vacuum concentration at 60°C to 30% of the initial volume.

[0031] In step 3, the alcohol precipitation is performed by adding 0.5 to 2 times the volume of the concentrate to the concentrate and allowing it to precipitate overnight; the drying is performed by freeze drying; before the drying, the precipitate is dissolved in distilled water and then the drying is performed.

[0032] Preferably, the amount of ethanol used is 1 times the volume of the concentrated liquid.

[0033] The soybean residue soluble dietary fiber prepared by the above method.

[0034] The application of soybean residue soluble dietary fiber prepared by the above method in the preparation of food and health products.

[0035] This invention aims to improve the extraction rate of SDF from soybean residue, reduce the raw material cost of SDF preparation, and improve the physicochemical properties of soybean residue SDF. Using fresh soybean residue as raw material, this invention pretreats the residue with phosphate buffer solution and optimizes the Penicillium fermentation process parameters through orthogonal experiments. The resulting soybean residue SDF powder has an SDF content of 40-60%. Compared with untreated dry soybean residue, the SDF content is increased by more than 5 times, and the structure is loose and porous with significantly improved solubility, demonstrating a significant effect in promoting the growth of beneficial intestinal flora. This invention provides a method for preparing soybean residue SDF with low raw material cost, simple preparation process, and good biological activity, and has potential applications in food and health products.

[0036] Beneficial effects:

[0037] Compared with existing technologies, the advantages of this invention are:

[0038] (1) In the preparation method of the present invention, the soybean residue pretreatment method is simple, the microbial culture medium has simple components, the fermentation cycle is short, the SDF content of soybean residue is significantly increased, and it is easy to realize industrialization.

[0039] (2) The soybean residue SDF prepared by the extended Penicillium fermentation method of this invention has a more loose and porous structure, significantly improved solubility, and has a significant effect on promoting the growth of beneficial intestinal flora, and has good application potential. Attached Figure Description

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0041] Figure 1 The SDF content in the soybean residue soluble dietary fiber powder obtained under different phosphate buffer pretreatment conditions in Example 2 is shown.

[0042] Figure 2 This is a schematic diagram of the transparent circles on the screening plate for Penicillium, Trichoderma reesei, Aspergillus niger, Trichoderma reesei, Trichoderma citrinum, and Trichoderma viride in Example 3.

[0043] Figure 3 The SDF content in the soybean residue soluble dietary fiber powder obtained by fermenting Penicillium under different fermentation conditions in Example 4 is shown.

[0044] Figure 4 The images show scanning electron microscope (SEM) images of the soybean residue soluble dietary fiber powders prepared by different methods in Example 5.

[0045] Figure 5 The OD of bacteria in the culture medium during the culture of *Lactobacillus plantarum* and *Bifidobacterium adolescentis* in Example 6. 600 value.

[0046] Figure 6 The pH value of the culture medium during the culture of Lactobacillus plantarum and Bifidobacterium adolescentis in Example 6. Detailed Implementation

[0047] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0048] The *Penicillium expansum* strain used in the following examples is a commercially available strain. Penicillium expansum CGMCC3.15402.

[0049] The method for preparing the extended Penicillium seed culture in the following examples is as follows: Mature extended Penicillium spores cultured on a PDA plate are washed off with sterile water to prepare a solution with a concentration of 10... 7 A spore suspension of 1 spore per mL was inoculated into the seed culture medium at an inoculation rate of 1%, and cultured on a shaker at 26℃ and 150 r / min for 24 h to obtain the extended Penicillium seed culture.

[0050] The seed culture medium formula is as follows: glucose 4.0 ~ 10.0 g / L, corn steep liquor dry powder 5.0 ~ 20.0 g / L; pH 6.0 ~ 7.0.

[0051] Example 1: Composition Analysis of Fresh Soybean Residue

[0052] Moisture content was determined according to the direct drying method in GB 5009.3-2016 "National Food Safety Standard - Determination of Moisture in Food"; dietary fiber content was determined according to GB 5009.88-2014 "National Food Safety Standard - Determination of Dietary Fiber in Food"; protein content was determined according to the Kjeldahl method in GB 5009.5-2016 "National Food Safety Standard - Determination of Protein in Food"; fat content was determined according to the Soxhlet extraction method in GB 5009.6-2016 "National Food Safety Standard - Determination of Fat in Food"; and ash content was determined according to GB 5009.4-2016 "National Food Safety Standard - Determination of Ash in Food". The results are shown in Table 1. The moisture content of fresh soybean residue is as high as 80%, and the dietary fiber content in the dry weight of soybean residue reaches 70-75%.

[0053] Table 1. Components and percentages of soybean residue

[0054]

[0055] Example 2 Screening of phosphate buffer

[0056] Fresh soybean residue was added to 1000 mL of 0.05 M citrate-disodium hydrogen phosphate buffer (CP), sodium dihydrogen phosphate-disodium hydrogen phosphate buffer (PN), and potassium dihydrogen phosphate-disodium hydrogen phosphate buffer (PK) at pH 5.5. The mass ratio of fresh soybean residue to buffer volume was 150 g : 1000 mL. The mixture was shaken at 25°C for 2 h to pretreat the fresh soybean residue, resulting in pretreated soybean residue. A blank control group was set up, in which sterile water was used instead of phosphate buffer for pretreatment of the soybean residue, with other treatment methods the same as the experimental groups.

[0057] Fermentation medium was prepared using pretreated soybean residue: sucrose and urea were added to the pretreated soybean residue, with 5 g of sucrose and 0.3 g of urea per liter of pretreated soybean residue, and the mixture was thoroughly mixed. The fermentation medium was sterilized at 121℃ for 15-20 min, cooled to room temperature, and then inoculated with Penicillium spores at a 10% v / v inoculum. Fermentation was carried out at 26℃, pH 6.5, and a rotation speed of 150 r / min for 30 h to obtain fermented soybean residue. The fermented soybean residue was centrifuged at 5000 r / min for 10 min, and the supernatant was collected. The supernatant was concentrated under vacuum at 60℃ to 30% of the initial volume to obtain a concentrate. An equal volume of ethanol was added to the concentrate for alcohol precipitation, and the precipitation was allowed to occur overnight. The precipitate was collected, dissolved in distilled water, and then freeze-dried to obtain soluble dietary fiber powder from soybean residue.

[0058] The soluble dietary fiber content in soybean residue soluble dietary fiber powder was determined according to GB 5009.88-2014 "National Food Safety Standard - Determination of Dietary Fiber in Food". The results are as follows: Figure 1 As shown in the figure. Using soluble dietary fiber content as the evaluation index, the phosphate buffer with the best pretreatment effect was screened.

[0059] from Figure 1 As can be seen, the proportion of soluble dietary fiber in the soybean residue soluble dietary fiber powder obtained after fermentation following phosphate buffer pretreatment was 25.5% to 29%, which was much higher than the 10% in the blank control group. Among them, the proportion of soluble dietary fiber in the soybean residue soluble dietary fiber powder obtained after pretreatment with citrate-disodium hydrogen phosphate buffer was the highest, at 29.2%.

[0060] Example 3 Screening of fermentation strains

[0061] 30 μL of bacterial suspension was taken from glycerol tubes containing *Penicillium expansum*, *Trichoderma reesei* (CICC 13052), *Aspergillus niger*, *Trichoderma reesei* (CGMCC 3.5218), *Trichoderma citrinum*, and *Trichoderma viride*, and spread onto PDA plates. The plates were incubated at 26°C for 4 days. The spores were then washed off the PDA plates with sterile water to prepare a spore concentration of 102. 7A spore suspension of 1 spores / mL was inoculated into PDA liquid medium at a 1% v / v inoculation rate and cultured at 26℃ and 150 r / min for 24 h to obtain seed culture. The seed culture was then added to fermentation medium (15 g / L sodium carboxymethyl cellulose, 5 g / L soybean meal, 1 g / L ammonium sulfate, 1 g / L dipotassium hydrogen phosphate, 0.5 g / L magnesium sulfate) at a 10% v / v inoculation rate and cultured at 26℃ and 150 r / min for 48 h. 10 μL of the fermentation broth was inoculated onto a screening plate (1 g / L sodium carboxymethyl cellulose, 1 g / L ammonium sulfate, 0.5 g / L magnesium sulfate heptahydrate, 1 g / L dipotassium hydrogen phosphate, 0.1 g / L Congo red, 20 g / L agar) and cultured at 26℃ for 4 days. The size of the transparent zone on the screening plate was then observed. Sodium carboxymethyl cellulose is a soluble cellulose. Cellulose hydrolase secreted by the strain can degrade sodium carboxymethyl cellulose in the screening plate, thereby forming a clear zone around the colony. The higher the activity of the cellulose hydrolase, the greater the degradation of sodium carboxymethyl cellulose and the larger the diameter of the clear zone.

[0062] The experimental results of this embodiment are as follows: Figure 2 As shown, Penicillium extended showed a significantly larger clear zone on the screening plate than the other five strains. Compared with Trichoderma reesei (CICC 13052), which has been shown to have a strong cellulase secretion capacity, Penicillium extended showed a stronger cellulase secretion capacity. Therefore, Penicillium extended was selected as the strain for further fermentation optimization.

[0063] Example 4: Single-factor optimization experiment to extend Penicillium fermentation culture conditions

[0064] The fermentation conditions for Penicillium extended were optimized.

[0065] 150 g of wet soybean residue was added to 1000 mL of 0.05 M citrate-disodium hydrogen phosphate buffer solution (pH 5.5). After shaking at 25 °C for 2 h, pretreated soybean residue was obtained. 5 g of sucrose and 0.3 g of urea were added to the pretreated residue, and the mixture was thoroughly mixed to obtain a fermentation medium. The medium was sterilized at 121 °C for 15-20 min, cooled to room temperature, and then inoculated with Penicillium spp. seed culture for fermentation. Other fermentation conditions were controlled the same as in Example 2. The soluble dietary fiber content in the soybean residue soluble dietary fiber powder obtained under different seed culture inoculation amounts (4%, 6%, 8%, 10%, 12%, 14% v / v), different fermentation pH (4.5, 5.0, 5.5, 6.0, 6.5, 7.0), and different fermentation times (24 h, 30 h, 36 h, 42 h, 48 h, 54 h) was investigated. The fermented soybean residue obtained from fermentation was processed according to the method in Example 2 to obtain soybean residue soluble dietary fiber powder, and the soluble dietary fiber content therein was determined.

[0066] In the experiment to explore the optimal pH conditions, the initial pH of the fermentation medium was first adjusted to 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0 respectively using citrate-disodium hydrogen phosphate buffer (pH=4.5~5.5) or potassium phosphate buffer (pH=6.0~7.0). The fermentation medium was then sterilized, cooled to room temperature, and inoculated with Penicillium spp. seed culture for fermentation. Other fermentation conditions were the same as in Example 2. Under different pH fermentation conditions, the soluble dietary fiber content in the obtained soybean residue soluble dietary fiber powder was as follows: Figure 3 As shown in a, the SDF content of soybean residue first increases and then decreases with increasing pH, reaching a maximum value of 34.6% at pH 6.5.

[0067] The soluble dietary fiber content in soybean residue soluble dietary fiber powder obtained under different fermentation times (24 h, 30 h, 36 h, 42 h, 48 h, 54 h) is as follows: Figure 3 As shown in b, the SDF content of soybean residue reached its highest value of 45.2% when the fermentation time was 30 h. If the fermentation time is too short, the bacterial cell mass of the strain is small in the early stage of fermentation, and the secretion of less cellulase is also small. If the fermentation time is too long, the original nutrients in the culture medium are exhausted, and the strain will consume SDF, resulting in a decrease in SDF content. Therefore, the optimal fermentation time is 30 h.

[0068] The soluble dietary fiber content in soybean residue soluble dietary fiber powder obtained under different seed liquid inoculation amounts (4%, 6%, 8%, 10%, 12%, 14% v / v) is as follows: Figure 3 As shown in Figure c, the SDF content first increases and then decreases with the increase of the inoculum amount, reaching 49.5% when the inoculum amount is 10% v / v.

[0069] Under the above optimal conditions (fermentation pH 6.5, fermentation time 30 h, inoculation amount 10% v / v), Penicillium extended was inoculated into the fermentation medium prepared in this embodiment and fermented. Other fermentation conditions were the same as in Example 2. After fermentation, the fermented soybean residue was processed according to the method in Example 2 to obtain soybean residue soluble dietary fiber powder, and the SDF content was determined to be 51.5%.

[0070] Example 5: Scanning electron microscopy analysis of SDF surface morphology characteristics

[0071] The microstructure of SDF (FSDF) obtained under the optimal fermentation conditions in Example 4 was characterized by SEM. SDF (BSDF) obtained from wet soybean residue by direct water extraction and SDF (PSDF) obtained after extraction with citrate-disodium hydrogen phosphate buffer (0.05 M, pH=5.5) were selected as controls. The results are as follows: Figure 4As shown, there are significant differences in the surface morphology and microstructure of the three SDFs. BSDF ( Figure 4 a and Figure 4 d) has a relatively smooth and uniform microstructure surface, dense texture, and small specific surface area, while PSDF ( Figure 4 b and Figure 4 e) shows a porous, wrinkled surface, which may be related to the decomposition of fiber macromolecules and the breakage of glycosidic bonds caused by chemical treatment. Phosphate buffer treatment can break down the rigid structure of soybean residue. FSDF, on the other hand, exhibits a looser, more porous microstructure. Figure 4 c and Figure 4 f) During fermentation and hydrolysis, the connections between the components of dietary fiber are disrupted, especially cellulose and hemicellulose. Therefore, FSDF has the loosest structure and the highest surface pore density.

[0072] Example 6: Effects of FSDF on the growth of Lactobacillus plantarum and Bifidobacterium adolescentis

[0073] Strain activation: *Lactobacillus plantarum* and *Bifidobacterium adolescentis* were inoculated at a 3% inoculum into lactic acid bacteria medium (5.0 g / L peptone, 2.0 g / L yeast extract, 1.0 g / L dipotassium hydrogen phosphate, 1.0 g / L diammonium hydrogen citrate, 2.5 g / L sodium acetate, 0.1 g / L magnesium sulfate, 0.04 g / L manganese sulfate) and bifidobacteria medium (10.0 g / L peptone, 5.0 g / L yeast extract, 8.0 g / L casein peptone, 1.0 g / L sodium chloride, 1.0 g / L dipotassium hydrogen phosphate, 1.0 g / L potassium dihydrogen phosphate, 0.02 g / L ferrous sulfate, 0.005 g / L manganese sulfate, 0.5 g / L L-cysteine) and incubated statically in an anaerobic environment at 37°C for 12 h.

[0074] Four sets of lactic acid bacteria culture media were prepared, one of which served as a blank control group without any added substances. The other three sets of lactic acid bacteria culture media contained FSDF at concentrations of 2.5 g / L, 5.0 g / L, and 10 g / L, respectively. Four sets of bifidobacteria culture media were prepared using the same method. Activated *Lactobacillus plantarum* and *Bifidobacterium adolescentis* were inoculated into the four sets of lactic acid bacteria culture media and the four sets of bifidobacteria culture media, respectively, with an inoculation rate of 3% v / v for *Lactobacillus* and 10% v / v for *Bifidobacterium*. The inoculated tubes were placed in an anaerobic environment at 37°C and incubated statically for 24 h. During the incubation period, samples were taken periodically to detect the OD (occurrence density) of the bacteria in the culture media. 600 and pH.

[0075] OD of Lactobacillus plantarum in culture medium during cultivation 600 Bifidobacterium adolescentis OD 600 The test results are as follows:Figure 5 a and Figure 5 As shown in b, the growth-promoting effect of FSDF on Lactobacillus increased with increasing concentration; the effects of 5 g / L and 10 g / L were comparable, both significantly stronger than the CK group. FSDF also significantly promoted the growth of Bifidobacterium, but the differences in growth-promoting effects among different concentrations of FSDF were not significant.

[0076] The pH values ​​of Lactobacillus plantarum culture medium and Bifidobacterium adolescentis culture medium during the culture period are as follows: Figure 6 a and Figure 6 As shown in b, the pH values ​​of the groups with different concentrations of FSDF were all lower than those of the control group. Different concentrations of FSDF had no significant effect on the pH of the culture medium; this phenomenon was consistent in both the *Lactobacillus plantarum* culture medium and the *Bifidobacterium adolescentis* culture medium.

[0077] The above results indicate that FSDF promotes the growth of both Lactobacillus plantarum and Bifidobacterium adolescentis. During their proliferation, Lactobacillus and Bifidobacterium produce a variety of organic acids, which lower the pH value of the intestine and inhibit the growth of harmful bacteria. The addition of FSDF can significantly reduce the pH value of the fermentation broth, which helps to improve the intestinal environment and maintain the balance of intestinal flora.

[0078] This invention provides a method and approach for preparing and applying soluble dietary fiber from soybean residue. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing soluble dietary fiber from soybean residue, characterized in that, Includes the following steps: Step 1: Add soybean residue to phosphate buffer solution, shake, and obtain pretreated soybean residue; Step 2: Add nutrients to the pretreated soybean residue obtained in Step 1, mix well, and prepare a fermentation culture medium. Inoculate Penicillium expansum into the fermentation culture medium for fermentation treatment to obtain fermented soybean residue. Step 3: Separate the fermented soybean residue obtained in Step 2 into solid and liquid components, collect the clear liquid, concentrate it to obtain a concentrated liquid, precipitate it with alcohol, collect the precipitate, and dry it to obtain soluble dietary fiber from soybean residue.

2. The preparation method according to claim 1, characterized in that, In step 1, the phosphate buffer is any one of citrate-disodium hydrogen phosphate buffer, sodium dihydrogen phosphate-disodium hydrogen phosphate buffer, and potassium dihydrogen phosphate-disodium hydrogen phosphate buffer; the concentration of the phosphate buffer is 0.01 ~ 0.5 mol / L, and the pH is 5.5 ~ 6.

5.

3. The preparation method according to claim 1, characterized in that, In step 1, the amount of soybean residue added is 100-250 g per liter of phosphate buffer; the shaking time is 1-4 h.

4. The preparation method according to claim 1, characterized in that, In step 2, the nutrients include sucrose and urea; the amount of sucrose added is 5 to 10 g per liter of pretreated soybean residue; the amount of urea added is 0.1 to 0.5 g per liter of pretreated soybean residue.

5. The preparation method according to claim 1, characterized in that, In step 2, the inoculation method of Penicillium expansum is as follows: Penicillium expansum spore suspension is inoculated into the seed culture medium at an inoculation rate of 1-10% v / v, and cultured at 25-32℃ and 150-220 r / min for 18-36 h to obtain the seed culture, which is then inoculated into the fermentation culture medium at an inoculation rate of 5-15% v / v. The concentration of the extended Penicillium spore suspension was 10. 5 ~ 10 7 per mL.

6. The preparation method according to claim 1, characterized in that, In step 2, the fermentation conditions are: temperature 25 ~ 32 ℃, pH 6.0 ~ 7.0, rotation speed 150 ~ 220 r / min, and fermentation time 24 ~ 48 h.

7. The preparation method according to claim 1, characterized in that, In step 3, the solid-liquid separation is centrifugation at 4000-6000 r / min for 10-20 min; the concentration is vacuum concentration at 50-60℃.

8. The preparation method according to claim 1, characterized in that, In step 3, the alcohol precipitation is performed by adding 0.5 to 2 times the volume of the concentrate to the concentrate and allowing it to precipitate overnight; the drying is performed by freeze drying; before the drying, the precipitate is dissolved in distilled water and then the drying is performed.

9. Soluble dietary fiber from soybean residue prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the soybean residue soluble dietary fiber according to claim 9 in the preparation of food and health products.

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