Strain screening method for improving soluble dietary fibers in pomace through liquid fermentation and application of strain screening method

Abstract

The invention discloses a strain screening method for improving the content of soluble dietary fibers in pomace through liquid fermentation and application, and the strain screening method comprises the following steps: (1) performing vacuum freeze drying on the pomace, grinding with liquid nitrogen, sieving with a 60-mesh sieve, and adding a proper amount of pure water to prepare a suspension with the solid-liquid ratio of 1: 25; (2) sterilizing the suspension, cooling, performing fermentation treatment on the suspension and ten food fermentation bacteria, and screening out single strains with high SDF extraction rate; (3) carrying out combined mixed fermentation by using the screened single strains; (4) screening out a mixed bacterium combination with high SDF extraction rate; and (5) analyzing influence factors of time, temperature and solid-liquid ratio, and screening out the optimal mixed fermentation process. The liquid fermentation technology is applied, and the method has the characteristics of high fermentation speed, high fermentation efficiency and high yield, and is simple in process, low in cost, simple in equipment structure, low in investment, low in energy consumption, suitable for large-scale production, high in mechanization degree and high in labor production efficiency.

Description

Technical Field

[0001] The present invention relates to a method for screening strains and its application for improving the content of soluble dietary fiber in pomace by liquid fermentation, belonging to the technical field of drug and food fermentation. Background Art

[0002] Rosa roxburghii Tratt is the fruit of the perennial deciduous shrub Rosa roxburghii Tratt of the Rosaceae family. It is rich in vitamin C, SOD, flavonoids and other trace elements, and has rich nutritional value. Modern pharmacological research has found that Rosa roxburghii Tratt has functions such as antioxidant, anti-aging, and regulating the body's immune function. In recent years, Rosa roxburghii Tratt products have been vigorously developed. The main products include fresh fruit juice, beverages added with Rosa roxburghii Tratt juice, and preserved fruits, etc. However, a large amount of pomace is generated during the processing and utilization of Rosa roxburghii Tratt. According to incomplete statistics, the amount of Rosa roxburghii Tratt pomace produced annually in Guizhou Province due to the production of fresh squeezed Rosa roxburghii Tratt juice exceeds 20,000 tons. Directly discarding it will cause environmental pollution and waste of resources. Therefore, it is urgent to study the development and reuse value of Rosa roxburghii Tratt pomace.

[0003] Research shows that Rosa roxburghii Tratt pomace contains more functional components, such as various components like dietary fiber (DF), vitamin C and flavonoids, etc. Among them, the content of dietary fiber is as high as more than 70%. Dietary fiber is the "seventh major nutrient" after carbohydrates, lipids, proteins, minerals, vitamins and water, and it is gradually becoming a hot topic in the food industry. According to its solubility, dietary fiber is divided into insoluble dietary fiber (IDF) and soluble dietary fiber (SDF). Insoluble dietary fiber can promote bowel movement and defecation; soluble dietary fiber has functions such as improving blood sugar, blood lipid, immune function, lowering blood pressure, and reducing inflammatory response. Research has found that the content of soluble dietary fiber in Rosa roxburghii Tratt pomace is relatively low, which is not conducive to the secondary development and utilization of its pomace resources. Appropriately increasing the proportion of soluble dietary fiber in Rosa roxburghii Tratt pomace can enhance the efficacy of its dietary fiber.

[0004] At present, the methods for increasing the content of soluble dietary fiber in pomace include physical method, chemical method, biological enzyme method, composite modification method and microbial fermentation method. Among them, microbial fermentation method is considered a relatively safe, efficient and low-cost method for preparing and improving high-quality dietary fiber. Microbial fermentation is to use the enzymes produced by probiotics under suitable growth conditions to decompose some components in dietary fiber, thereby changing its structure and properties.

[0005] At present, the research on soluble dietary fiber in Rosa roxburghii Tratt pomace mainly focuses on the extraction and physicochemical property analysis of soluble dietary fiber, and there are few reports on the screening of fermentation strains for improving the content of soluble dietary fiber in Rosa roxburghii Tratt pomace by liquid fermentation method. Different fermentation strains have different effects on the modification of dietary fiber. At present, it is urgent to screen strains for improving the content of soluble dietary fiber in pomace from numerous probiotics and fermenting bacteria. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for screening strains and its application for improving the content of soluble dietary fiber in pomace by liquid fermentation, so as to overcome the above-mentioned deficiencies of the prior art.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for screening strains for improving the content of soluble dietary fiber in pomace by liquid fermentation, comprising the following steps:

[0009] (1) After vacuum freeze-drying the pomace, grind it with liquid nitrogen through a 60-mesh sieve, weigh an appropriate amount of pomace powder, put it into a conical flask, add an appropriate amount of pure water to make a suspension with a material-liquid ratio of 1:25, seal it with a sealing film and place it in a water bath for pasteurization;

[0010] (2) After the suspension is sterilized and cooled, ferment it with ten kinds of food fermentation bacteria, and respectively compare the SDF extraction rates of fermentation and non-fermentation to screen out the top three single fermentation strains in terms of SDF extraction rate;

[0011] (3) Use the selected single strains for combined mixed fermentation, and use the SDF extraction rate as the screening index;

[0012] (4) According to the SDF extraction rate after fermentation, screen out the mixed strain combination with a high SDF extraction rate;

[0013] (5) Use the response surface method to analyze the influencing factors of fermentation time, temperature and material-liquid ratio for this mixed strain combination, and screen out the best process for mixed strain fermentation;

[0014] (7) Finally, obtain the mixed strain combination with the best effect on modifying the dietary fiber of pomace, the best fermentation time, fermentation temperature and fermentation material-liquid ratio.

[0015] As a preferred solution, the ten kinds of food fermentation bacteria in step (2) are Aspergillus oryzae, Aspergillus niger, Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus and Streptococcus thermophilus.

[0016] When the pomace is Rosa roxburghii Tratt pomace, it includes the following steps:

[0017] (1) After the Rosa roxburghii Tratt fruit pomace is vacuum freeze-dried, it is ground with liquid nitrogen and passed through a 60-mesh sieve. Weigh 8 g of the Rosa roxburghii Tratt fruit pomace powder, put it into a 500 mL conical flask, add 200 mL of pure water to make a suspension with a solid-liquid ratio of 1:25, seal it with a sealing film and place it in a water bath for pasteurization;

[0018] (2) After the suspension in step (1) is sterilized and cooled, take ten kinds of food fermentation bacteria Aspergillus oryzae, Aspergillus niger, Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus, and culture them at an inoculation amount of 5%, a rotation speed of 180 r / min, a temperature of 25 °C and natural pH for 24 h;

[0019] (3) Centrifuge the fermented Rosa roxburghii Tratt fruit pomace fermentation broth in step (2) at 4200 r / min for 15 min to obtain the supernatant and precipitate; Extract soluble dietary fiber SDF from the supernatant: After adding 250 μL of heat-stable α-amylase, react at 95 °C for 35 min; Adjust the pH to 8.0, add 500 μL of protease, and incubate at 60 °C for 30 min; Then add 25 mL of 3 mol / L acetic acid solution, shake well appropriately; Adjust the pH value to 4.5, and then add 500 μL of amylosucrase and continue to digest enzymatically at 60 °C in a water bath for 35 minutes. The above is the enzymatic hydrolysis operation; While it is hot, add 4 times the volume of 95% ethanol at 60 °C and let it stand overnight. Wet a crucible with a constant weight with appropriate 95% ethanol and start suction filtration; Measure 15 mL of 78% ethanol with a measuring cylinder and wash twice, then measure 15 mL of 95% ethanol and wash twice, and finally measure 10 mL of acetone and wash twice, dry and weigh to obtain SDF1;

[0020] (4) Extract soluble dietary fiber SDF and insoluble dietary fiber IDF from the precipitate: After the precipitate prepared in step (3) is vacuum freeze-dried for 1-2 days, grind it finely, weigh it, transfer it to a triangular flask, add 200 ml of MES-TRIS buffer solution and perform the same enzymatic hydrolysis operation as the supernatant. Then centrifuge the enzymatic hydrolysate at 4200 r / min for 15 minutes. The obtained precipitate is dried and weighed, which is the insoluble dietary fiber IDF. The supernatant is added with 4 times the volume of 95% ethanol at 60 °C and let it stand overnight. What is obtained by suction filtration is the soluble dietary fiber SDF2; The sum of the two obtained SDFs (SDF1 + SDF2) divided by the total amount of Rosa roxburghii Tratt fruit pomace is the SDF extraction rate; Screen out the top three single fermentation strains with the highest SDF extraction rate;

[0021] (5) Mix and ferment the strains screened in step (4);

[0022] (6) Using the SDF extraction rate after fermentation as the response value, screen out the mixed bacterial combinations with obvious fermentation effects;

[0023] (7) Use the best mixed strain combination in step (6) to analyze the influencing factors of fermentation time, temperature, and solid-liquid ratio;

[0024] (8) Based on the change in the SDF extraction rate, finally determine the best mixed strain combination, fermentation time, fermentation temperature, and solid-liquid ratio for modifying dietary fiber from Rosa roxburghii Tratt pomace.

[0025] As an optimization, the best mixed strain combination with the highest SDF extraction rate in step (6) is Lactobacillus helveticus: Lactobacillus bulgaricus: Streptococcus thermophilus, and the mixed strain ratio is 1:1:1.

[0026] As an optimization, in step (8), the best fermentation time is 23 h, the best fermentation temperature is 26 °C, and the best solid-liquid ratio is 1:28.

[0027] The present invention also provides a method for improving soluble dietary fiber in Rosa roxburghii Tratt pomace by liquid fermentation, comprising the following steps:

[0028] (1) After vacuum freeze-drying Rosa roxburghii Tratt pomace, grind it with liquid nitrogen through a 60-mesh sieve. Weigh 8 g of Rosa roxburghii Tratt pomace powder, put it into a 500 mL conical flask, add 200 mL of pure water to make a 1:28 solid-liquid ratio suspension, seal it with a sealing film, and place it in a water bath for pasteurization;

[0029] (2) After sterilizing the suspension in (1) and cooling it, take Lactobacillus helveticus: Lactobacillus bulgaricus: Streptococcus thermophilus with a mixed strain ratio of 1:1:1, ferment for 23 h at an inoculation amount of 5%, a rotation speed of 180 r / min, a temperature of 26 °C, and natural pH.

[0030] Application of Lactobacillus helveticus, Lactobacillus bulgaricus, and Streptococcus thermophilus in improving the content of soluble dietary fiber in Rosa roxburghii Tratt pomace by liquid fermentation.

[0031] Beneficial effects: Compared with the prior art, the present invention uses liquid fermentation technology, which is different from traditional solid fermentation, and has the characteristics of fast fermentation speed, high fermentation efficiency, and high yield. Moreover, the present invention strictly follows the sterilization treatment during the fermentation process, and the addition of edible strains greatly avoids the contamination of miscellaneous bacteria. The process of the present invention is simple, with low cost, simple equipment structure, low investment, low energy consumption, suitable for large-scale production, high mechanization degree, and high labor productivity. The present invention first uses the method of screening multiple strains for fruit pomace to improve the SDF extraction rate as the inspection index and achieves remarkable results, turning fruit pomace into treasure, providing new ideas for the in-depth development and utilization of fruit pomace resources, and providing a new technical route for the transformation and application of fruit pomace. Brief Description of the Drawings

[0032] Figure 1 is the process flow chart of the present invention.

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Specific Embodiments

[0034] Taking Rosa roxburghii Tratt pomace as an example, the specific steps are as follows:

[0035] 1. Experimental Medicinal Materials

[0036] The experimental medicinal material, Rosa roxburghii Tratt pomace, was purchased from Guizhou Tongrentang.

[0037] 2. Experimental Bacterial Strains

[0038] The experimental bacterial strains are all freeze-dried bacterial strains, which were all purchased from the China Center for Industrial Culture Collection and were activated according to the relevant instructions. The specific bacterial strains are shown in Table 1.

[0039] Table 1 Edible Fungal Strains

[0040]

[0041]

[0042] 3. Culture Media

[0043] MRS Medium: 10 g of casein peptone, 10 g of beef extract, 5 g of yeast powder, 5 g of glucose, 1 g of Tween 80, 2 g of dipotassium hydrogen phosphate, 5 g of sodium acetate, 2 g of diammonium citrate, 0.2 g of MgSO4·7H2O, 0.05 g of MnSO4·H2O, 15 g of agar powder, 1 L of distilled water. Prepared by oneself. Mainly applicable to Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus

[0044] PDA Medium: 1 L of potato extract (potato powder), 20 g of glucose, 15 g of agar. Prepared by oneself. Mainly applicable to Aspergillus oryzae, Aspergillus niger.

[0045] Malt Extract Agar Medium: 1 L of malt extract, 15 g of agar. Prepared by oneself. Mainly applicable to Saccharomyces cerevisiae.

[0046] Nutrient Broth Agar Medium: 5 g of peptone, 3 g of beef extract, 15 g of sodium chloride. Prepared by oneself. Mainly applicable to Bacillus subtilis.

[0047] 4. Experimental Methods

[0048] (1) After vacuum freeze-drying the Rosa roxburghii Tratt pomace, it was ground with liquid nitrogen through a 60-mesh sieve. 8 g of Rosa roxburghii Tratt pomace powder was weighed and placed in a 500 mL conical flask, and 200 mL of pure water was added to make a suspension with a material-liquid ratio of 1:25. It was sealed with a sealing film and placed in a water bath for pasteurization;

[0049] (2) After the suspension was sterilized and cooled, ten food fermentation bacteria, Aspergillus oryzae, Aspergillus niger, Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus, and Streptococcus thermophilus, were taken and cultured at an inoculation amount of 5%, a rotation speed of 180 r / min, a temperature of 25 °C, and natural pH for 24 h. One bottle was used as a blank control;

[0050] The mixed bacteria combinations and ratios are shown in Table 2 below.

[0051] Table 2 Mixed bacteria combinations and ratios

[0052]

[0053]

[0054] (3) The fermented Rosa roxburghii Tratt pomace fermentation broth in (2) was centrifuged (4200 r / min) for 15 min to obtain the supernatant and precipitate. For the extraction of soluble dietary fiber (SDF) from the supernatant: After adding 250 μL of thermostable α-amylase (10000 U / mL), react at 95 °C for 35 min; adjust the pH to 8.0, add 500 μL of protease (400 U / mL), and incubate at 60 °C for 30 min; then add 25 mL of 3 mol / L acetic acid solution and shake well appropriately. Adjust the pH value to 4.5, and then add 500 μL of amylosucrase (2000 U / mL) and continue to digest enzymatically at 60 °C in a water bath for 35 minutes. The above is the enzymatic hydrolysis operation. While it is hot, add 4 times the volume of 95% ethanol at 60 °C and let it stand overnight. Moisten a crucible with a constant weight with appropriate 95% ethanol and start suction filtration. Measure 15 mL of 78% ethanol with a measuring cylinder and wash twice, then measure 15 mL of 95% ethanol and wash twice, and finally measure 10 mL of acetone and wash twice, dry and weigh to obtain SDF1;

[0055] (4) For the extraction of soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) from the precipitate: After the precipitate prepared in (3) was vacuum freeze-dried for 1 - 2 days, ground finely, weighed, transferred to an Erlenmeyer flask, added 200 ml of MES-TRIS buffer solution, and then carried out the same enzymatic hydrolysis operation as the supernatant. After that, the enzymatic hydrolysis solution was centrifuged (4200 r / min) for 15 minutes. The obtained precipitate was dried and weighed to obtain the insoluble dietary fiber (IDF). The supernatant was added with 4 times the volume of 95% ethanol at 60 °C and let it stand overnight. What was obtained by suction filtration was the soluble dietary fiber (SDF2). The sum of the two obtained SDFs (SDF1 + SDF2) divided by the total amount of Rosa roxburghii Tratt pomace is the SDF extraction rate. Screen out the top three single fermentation strains with the highest SDF extraction rate in single-bacteria fermentation.

[0056] (5) Mix the three strains screened in (4) for mixed fermentation (the mixed strain combinations and ratios are shown in Table 2), and culture them for 24 h under the conditions of the same inoculation amount of 5%, rotation speed of 180 r / min, temperature of 25 °C, and natural pH;

[0057] (6) Screen the mixed strain combinations with obvious fermentation effects according to the extraction rate of SDF after fermentation;

[0058] (7) Use the best mixed strain combination in (6) to analyze the influencing factors of time, temperature, and solid-liquid ratio;

[0059] (8) Based on the change in the extraction rate of SDF, finally determine the best mixed strain combination, fermentation time, fermentation temperature, and solid-liquid ratio for modifying dietary fiber from Rosa roxburghii Tratt pomace.

[0060] Use the response surface software Design-Expert 12 to design the experimental scheme. According to the results of the single-factor experiments, select the best mixed strain combination, and use this mixed strain combination to conduct an experimental design with three factors and three levels for fermentation temperature, fermentation time, and fermentation solid-liquid ratio. There are 17 experimental points in the experimental scheme, and the response value is the extraction rate of SDF.

[0061] 5. Experimental results

[0062] Through single-strain and mixed-strain fermentation experiments, it is found that the best mixed strain combination for modifying dietary fiber from Rosa roxburghii Tratt pomace is Lactobacillus helveticus, Lactobacillus bulgaricus, and Streptococcus thermophilus. Therefore, these three strains are selected for mixed fermentation.

[0063] Use the response surface software Design-Expert 12 to design a table for temperature, solid-liquid ratio, time, and SDF extraction rate; according to the optimization of data processing by Box-Behnken in the response surface software Design-Expert 12, the optimal fermentation time, fermentation temperature, and fermentation solid-liquid ratio that maximize the SDF extraction rate are 22.7 h, 26.08 °C, and 1:27.78, respectively. Under these three optimal factors, the SDF extraction rate is 12.36%, which is 54.11% higher than the SDF content (8.02%) in the pomace before fermentation.

[0064] Considering the actual situation, the optimal fermentation time, fermentation temperature, and fermentation solid-liquid ratio are 23 h, 26 °C, and 1:28, respectively. Thus, the best preparation method for multi-strain fermentation of Rosa roxburghii Tratt pomace is obtained.

[0065] In addition to the above-mentioned Rosa roxburghii Tratt pomace, this method can also be applied to the liquid fermentation of other pomaces to increase the content of soluble dietary fiber in the pomaces.

[0066] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for screening bacterial strains for increasing soluble dietary fiber in pomace by liquid fermentation, characterized in that: The following steps are involved: (1) After the pomace is freeze-dried in vacuum, it is ground with liquid nitrogen and passed through a 60-mesh sieve. An appropriate amount of pomace powder is weighed and placed in a conical flask. An appropriate amount of pure water is added to make a suspension with a solid-liquid ratio of 1:

25. The suspension is sealed with a sealing film and placed in a water bath for pasteurization. (2) After the suspension was sterilized and cooled, it was inoculated with ten bacterial strains for food fermentation, and the soluble dietary fiber (SDF) extraction rates of fermented and unfermented pomace were compared, and the top three single fermentation bacterial strains with the highest SDF extraction rates were selected; (3) Using the single fermentation strains screened out to carry out combined mixed strain fermentation, the SDF extraction rate is used as the screening index; (4) Based on the SDF extraction rate after fermentation, a mixed bacterial combination with a high SDF extraction rate is selected; (5) Response surface methodology was used to analyze the influencing factors of fermentation time, temperature, and material-liquid ratio of this mixed bacteria combination, and the optimal mixed bacteria fermentation process was screened out; (7) Finally, the mixed bacteria combination with the best effect on modifying the dietary fiber of pomace, the optimal fermentation time, fermentation temperature and fermentation liquid ratio were obtained.

2. The method for screening strains for improving soluble dietary fiber in pomace by liquid fermentation according to claim 1, characterized in that: The ten food fermentation bacteria in step (2) are Aspergillus oryzae, Aspergillus niger, Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus and Streptococcus thermophilus.

3. The method for screening strains for improving soluble dietary fiber in pomace by liquid fermentation according to claim 1, characterized in that: The pomace is roxburghii pomace, and the method comprises the following steps: (1) After vacuum freeze-drying, the pomace of the roxburghii fruit was ground with liquid nitrogen through a 60-mesh sieve, 8 g of the pomace powder was weighed and placed in a 500 mL conical flask, 200 mL of pure water was added to make a suspension with a solid-liquid ratio of 1:25, and the suspension was sealed with a sealing film and placed in a water bath for pasteurization; (2) sterilizing the suspension of step (1) and cooling it, taking ten kinds of food fermentation bacteria Aspergillus oryzae, Aspergillus niger, Saccharomyces cerevisiae, Bacillus subtilis, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus, and Streptococcus thermophilus, and culturing them for 24 hours at an inoculation amount of 5%, a rotation speed of 180 r / min, a temperature of 25° C., and a natural pH; (3) The fermented roxburghii pomace fermented liquid in step (2) was centrifuged at 4200 r / min for 15 min to obtain a supernatant and a precipitate; the supernatant was used to extract soluble dietary fiber SDF: 250 μL of heat-stable α-amylase was added, and the mixture was reacted at 95° C. for 35 min; the pH was adjusted to 8.0, 500 μL of protease was added, and the mixture was incubated at 60° C. for 30 min; 25 mL of 3 mol / L acetic acid solution was then added, and the mixture was shaken appropriately to mix; the pH value was adjusted to 4.5, and 500 μL of amylotransferase was added to digest and hydrolyze the mixture in a 60° C. water bath for 35 min, and the above was the enzymatic hydrolysis operation; 4 times of 60° C. 95% ethanol was added while hot and allowed to stand overnight, and a crucible with a constant weight was moistened with an appropriate amount of 95% ethanol, and suction filtration was started; 15 mL of 78% ethanol was measured with a measuring cylinder and washed twice, and then 15 mL of 95% ethanol was measured and washed twice, and finally 10 mL of acetone was measured and washed twice, and the mixture was dried and weighed to obtain SDF1; (4) extracting soluble dietary fiber SDF and insoluble dietary fiber IDF from the precipitate: freeze-dry the precipitate prepared in step (3) under vacuum for 1-2 days, grind it into powder, weigh it, transfer it to a triangular flask, add 200 ml of MES-TRIS buffer solution, and perform the same enzymatic hydrolysis operation as the supernatant. Then, centrifuge the enzymatic hydrolyzate at 4200 r / min for 15 minutes, dry the obtained precipitate, weigh it, and obtain the insoluble dietary fiber IDF. Add four times of 60° C. 95% ethanol to the supernatant and let it stand overnight. The soluble dietary fiber SDF2 is obtained by suction filtration. The sum of the SDF obtained twice (SDF1+SDF2) divided by the total amount of roxburghii pomace is the SDF extraction rate. The top three strains of SDF extraction rate are selected. (5) subjecting the strains screened in step (4) to mixed fermentation; (6) Based on the SDF extraction rate after fermentation, screen the mixed bacteria combination with obvious fermentation effect; (7) using the best mixed bacteria combination in step (6) to analyze the influencing factors of time, temperature, and material-liquid ratio; (8) Using the change in SDF extraction rate, we finally determined the best mixed bacteria combination, best fermentation time, best fermentation temperature, and best solid-liquid ratio for modifying the dietary fiber of sea buckthorn pomace.

4. The method for screening strains for improving soluble dietary fiber in pomace by liquid fermentation according to claim 3, characterized in that: In step (6), the mixed bacteria combination with the highest SDF extraction rate is Lactobacillus helveticus: Lactobacillus bulgaricus: Streptococcus thermophilus, and the mixed bacteria ratio is 1:1:

1.

5. The method for screening strains for improving soluble dietary fiber in pomace by liquid fermentation according to claim 3, characterized in that: In step (8), the best fermentation time is 23 h, the best fermentation temperature is 26° C., and the best solid-liquid ratio is 1:

28.

6. A method for increasing soluble dietary fiber in roxburghii pomace by liquid fermentation, characterized in that: The following steps are involved: (1) After vacuum freeze-drying, the pomace of the roxburghii fruit was ground with liquid nitrogen through a 60-mesh sieve, 8 g of the pomace powder was weighed and placed in a 500 mL conical flask, 200 mL of pure water was added to make a suspension with a solid-liquid ratio of 1:28, and the suspension was sealed with a sealing film and placed in a water bath for pasteurization; (2) After sterilizing the suspension of step (1), cool it and take Lactobacillus helveticus: Lactobacillus bulgaricus: Streptococcus thermophilus in a mixed ratio of 1:1:1, and ferment it for 23 hours at an inoculum amount of 5%, a rotation speed of 180 r / min, a temperature of 26° C. and a natural pH.

7. Application of Lactobacillus helveticus, Lactobacillus bulgaricus and Streptococcus thermophilus in liquid fermentation to increase the soluble dietary fiber content of pomace.

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