Method for producing reducing sugar by fermenting sugar beet pulp with aspergillus niger at low cost and application

Abstract

The invention discloses a method for producing reducing sugar by fermenting sugar beet pulp with aspergillus niger at low cost, which comprises the following steps: mixing the sugar beet pulp with bran, sterilizing and drying, adding a nutrient solution, aspergillus niger solution and PDB culture solution, and carrying out solid fermentation to produce the reducing sugar, the PDB culture solution contains potato powder and glucose. According to the method, the aspergillus niger is cultured through the cheap potato pulp culture medium, cellulase, lipase, protease, pectinase and other enzyme systems generated by the aspergillus niger are used for destroying plant cell walls of the sugar beet pulp, degrading fiber substances and converting the fiber substances into small-molecule reducing sugar, the utilization rate of the fiber substances is increased, and a new way is provided for comprehensive utilization of sugar beet pulp resources.

Description

Technical Field

[0001] The invention belongs to the technical field of biological fermentation, and particularly relates to a method for producing reducing sugar by fermenting beet pulp with Aspergillus niger at low cost and application thereof. Background Art

[0002] Beet pulp is a byproduct of sugar production. It is the residue left after beet roots and tubers are soaked and squeezed to extract the sugar solution. After soaking and extraction, the beet pulp still contains rich nutrients such as protein, polysaccharides, amino acids, and crude fiber. Therefore, beet pulp has high nutritional value and is currently used as feed, fertilizer, and biomass fuel. However, the amount of solid beet pulp waste generated during beet sugar production is increasing, and the current processing rate is far lower than the output rate of beet pulp, causing increasing environmental pollution. Summary of the Invention

[0003] The present invention aims to effectively improve resource utilization efficiency during sugar beet production by providing a low-cost method for fermenting sugar beet pomace to produce reducing sugars using Aspergillus niger. This method involves culturing Aspergillus niger in an inexpensive potato pomace culture medium and utilizing enzymes such as cellulase, lipase, protease, and pectinase produced by the Aspergillus niger to break down the cell walls of the sugar beet pomace, degrading fibrous materials and converting them into small-molecule reducing sugars. This method improves the utilization rate of fibrous materials and provides a new approach for the comprehensive utilization of sugar beet pomace resources.

[0004] The purpose of the present invention can be achieved by the following measures:

[0005] A method for producing reducing sugars by fermenting beet pulp with Aspergillus niger at low cost comprises the following steps: mixing beet pulp with bran, sterilizing and drying the mixture, adding a nutrient solution, an Aspergillus niger solution and a PDB culture solution, and performing solid fermentation to produce reducing sugars; wherein the PDB culture solution contains potato flour and glucose (preferably anhydrous glucose).

[0006] The potato flour in the present invention is freeze-dried potato residue powder, potato water extract powder or potato extract powder, preferably one or more of freeze-dried potato residue powder and potato water extract powder, more preferably one or more of freeze-dried potato residue powder and fresh potato water extract powder.

[0007] Potato water extract powder is obtained by dicing potatoes, boiling them in water, and then removing the potato residue. A specific method for preparing potato water extract powder is as follows: peel and chop 5-20 parts of potatoes, mix them with 30-80 parts of pure water, bring to a boil, and boil for 10-30 minutes. The supernatant is filtered and evaporated to remove moisture. Fresh potatoes are preferably used to obtain fresh potato water extract powder.

[0008] PDB culture medium can be prepared using potato flour according to component requirements, or it can be directly prepared using potatoes or fresh potatoes during the preparation of water extract powder. One method for directly using potatoes to prepare PDB culture medium is as follows: take 5 to 20 parts of potatoes, peel, cut into pieces or crush them, and then mix them with 30 to 80 parts of pure water, heat them to boiling water and boil them for 10 to 30 minutes, filter the supernatant, and add 0.5 to 2 parts of anhydrous glucose.

[0009] The PDB culture solution of the present invention may contain the following components in parts by weight: 0.1 to 0.4 parts of potato flour, 0.5 to 2 parts of glucose, and 30 to 80 parts of water.

[0010] In a preferred embodiment, the PDB culture medium may contain the following components in parts by weight: 0.1-0.4 parts of potato flour, 0.5-2 parts of glucose, and 50 parts of water.

[0011] In a more preferred embodiment, the PDB culture medium may contain the following components in parts by weight: 0.2 parts of potato flour, 1 part of glucose, and 50 parts of water.

[0012] The Aspergillus niger liquid in the present invention contains Aspergillus niger. The Aspergillus niger used in the examples of the present invention is CMCC 98003 purchased from Shanghai Collection Biotechnology Center.

[0013] The nutrient solution of the invention contains yeast powder, peptone, ammonium sulfate, potassium dihydrogen phosphate, magnesium sulfate heptahydrate, manganese sulfate, ferrous sulfate heptahydrate and water.

[0014] In a preferred embodiment, the weight composition of the components in the nutrient solution is: 0.5-2 parts of yeast powder, 0.3-0.7 parts of peptone, 1-3 parts of ammonium sulfate, 0.5-2 parts of potassium dihydrogen phosphate, 0.3-0.7 parts of magnesium sulfate heptahydrate, 0.2-0.5 parts of manganese sulfate, 0.03-0.12 parts of ferrous sulfate heptahydrate, and 15-20 parts of water.

[0015] In a more preferred embodiment, the weight composition of the components in the nutrient solution is: 1 part yeast powder, 0.5 part peptone, 2 parts ammonium sulfate, 1 part potassium dihydrogen phosphate, 0.5 part magnesium sulfate heptahydrate, 0.35 part manganese sulfate, 0.07 part ferrous sulfate heptahydrate, and 18 parts water.

[0016] In the method of the present invention, the weight proportions of the components during solid fermentation are: 5-15 parts of beet pulp, 1-4 parts of bran, 5-15 parts of nutrient solution, 1-5 parts of black aspergillus solution, and 4-12 parts of PDB culture solution.

[0017] In a preferred embodiment, the weight proportions of the components during solid fermentation are: 8-12 parts of beet pulp, 1-3 parts of bran, 8-12 parts of nutrient solution, 1-3 parts of Aspergillus niger solution, and 6-10 parts of PDB culture solution.

[0018] In a more preferred embodiment, the weight proportions of the components during solid fermentation are as follows: 10 parts of beet pulp, 2 parts of bran, 10 parts of nutrient solution, 2 parts of Aspergillus niger solution, and 8 parts of PDB culture solution.

[0019] The sterilization operation in the present invention can be: high pressure sterilization at 120-123° C. for 15-25 minutes.

[0020] The drying operation in the present invention may be: drying at 60° C. to 70° C. for 15 to 25 hours.

[0021] The solid fermentation in the present invention is preferably carried out under a sterile environment.

[0022] The temperature of the solid fermentation in the present invention is 28 to 32° C., preferably 30° C. The time of the solid fermentation is 2 to 10 days, preferably 5 to 7 days.

[0023] The method of the present invention is particularly suitable for preparing reducing sugar using beet pulp as raw material.

[0024] Beneficial effects of the present invention: The present invention utilizes potato powder (especially freeze-dried potato residue powder or fresh potato water extract powder) as a cheap PDA culture medium raw material that is conducive to the growth of Aspergillus niger. On this basis, Aspergillus niger is used to ferment beet residue, and Aspergillus niger is used to degrade the components in the beet residue that are difficult to utilize, thereby accelerating the saccharification process of the beet residue, and thus preparing reducing sugar. The method for preparing reducing sugar from beet residue by solid-state fermentation of Aspergillus niger provided by the present invention is practical, and the reducing sugar produced can also be used as saccharification feed or industrial raw material, providing a new option for the comprehensive utilization of beet residue resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a colony morphology diagram of Aspergillus niger of the present invention on different PDA at different times. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0027] The present invention will now be further described with reference to specific examples. The following examples are intended only to illustrate the present invention and are not intended to limit its contents. Experimental conditions not specified in the examples are generally based on conventional conditions or those recommended by the reagent company. Reagents and consumables used in the following examples are commercially available unless otherwise specified.

[0028] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings. The advantages and features of the present invention will become clearer as the description proceeds. However, the embodiments are merely exemplary and do not limit the scope of the present invention in any way. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements fall within the scope of protection of the present invention.

[0029] Bacterial strains and culture medium

[0030] 1.1 Bacterial strain

[0031] Aspergillus niger, No. CMCC 98003, was purchased from Shanghai Collection Biotechnology Center.

[0032] 1.2 Culture medium

[0033] (1) Fresh PDA medium (APDA): Wash, peel, and cut fresh potatoes into small pieces. Weigh 100 g of the medium, add 500 mL of pure water, and boil for 20 minutes. Remove the potato residue and add water to 500 mL. Then add 10 g of anhydrous glucose and 10 g of agar.

[0034] (2) Commercial rapid PDA medium (BPDA): weigh 2 g of potato extract powder, add 10 g of anhydrous glucose and 10 g of agar, and add 500 mL of water;

[0035] (3) Potato residue PDA medium (CPDA): Weigh 2 g of potato residue freeze-dried powder, add 10 g of anhydrous glucose and 10 g of agar, and add 500 mL of water;

[0036] (4) Solid fermentation nutrient solution: Weigh 1.00 g yeast powder, 0.50 g peptone, 2.00 g ammonium sulfate, 1.00 g potassium dihydrogen phosphate, 0.50 g magnesium sulfate heptahydrate, 0.35 g manganese sulfate, 0.07 g ferrous sulfate heptahydrate, and add 18 mL of water;

[0037] Preparation of culture medium: After all the culture medium components are fully dissolved, autoclave at 121°C for 20 minutes.

[0038] 1.3PDB culture medium: Weigh 2 g of freeze-dried potato residue powder, add 10 g of anhydrous glucose, add 500 mL of water, mix thoroughly, and autoclave at 121°C for 20 minutes.

[0039] Beet pulp: The free reducing sugar content of the beet pulp used in each example was determined to be 0.122 mg / g.

[0040] Bran: The free reducing sugar content of the bran used in each example was determined to be 0.015 mg / g.

[0041] Example 1

[0042] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0043] In a cleanroom, 100 μL of nutrient solution, 10 μL of bacterial culture, and 90 μL of PDB culture medium were added to a test tube of sugar beet pulp. The inoculum size was 5%. After completion of the inoculation, the test tube was placed in a 30°C incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 10.4006 mg / g. After four days of fermentation, the reducing sugar content reached 9.0121 mg / g. After six days of fermentation, the reducing sugar content reached 14.7902 mg / g.

[0044] Example 2

[0045] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0046] In a cleanroom, 100 μL of nutrient solution, 20 μL of bacterial culture, and 80 μL of PDB culture medium were added to a test tube of sugar beet pulp. The inoculum was 10%. After completion of the inoculation, the test tube was placed in a 30°C incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 12.1168 mg / g. After four days of fermentation, the reducing sugar content reached 9.9608 mg / g. After six days of fermentation, the reducing sugar content reached 16.7522 mg / g.

[0047] Example 3

[0048] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0049] In a cleanroom, 100 μL of nutrient solution, 30 μL of bacterial culture, and 70 μL of PDB culture medium were added to a test tube of sugar beet pulp. The inoculum size was 15%. After completion of the inoculation, the test tube was placed in a 30°C incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 8.7448 mg / g. After four days of fermentation, the reducing sugar content reached 7.7616 mg / g. After six days of fermentation, the reducing sugar content reached 14.2297 mg / g.

[0050] Example 4

[0051] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0052] In a cleanroom, 100 μL of nutrient solution, 40 μL of bacterial culture, and 60 μL of PDB culture medium were added to a test tube of sugar beet pulp. The inoculum was 20%. After completion of the inoculation, the test tube was placed in a 30°C incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 8.1670 mg / g. After four days of fermentation, the reducing sugar content reached 7.7401 mg / g. After six days of fermentation, the reducing sugar content reached 11.7934 mg / g.

[0053] Example 5

[0054] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0055] In a cleanroom, 100 μL of nutrient solution, 50 μL of bacterial culture, and 50 μL of PDB culture medium were added to a test tube of sugar beet pulp. The inoculum size was 25%. After completion of the inoculation, the test tube was placed in a 30°C incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 7.4943 mg / g. After four days of fermentation, the reducing sugar content reached 7.3520 mg / g. After six days of fermentation, the reducing sugar content reached 11.3191 mg / g.

[0056] Example 6: Investigation of the growth of Aspergillus niger on different PDA media

[0057] Use a pipette to transfer 10 μL of Aspergillus niger culture to 1 mL of sterile water and pipette evenly. Place 5 μL of Aspergillus niger culture on the center of each PDA plate and incubate at 30°C for 24 to 72 hours. Observe and record the colony diameter and morphology daily.

[0058] Table 1 Growth status of Aspergillus niger on different PDA at different times

[0059]

[0060] As shown in Table 1, at 24 hours of incubation, the colony diameters of A. niger on APDA and BPDA were larger than those on CPDA. At 48 and 72 hours of incubation, the order of the inner diameters of the A. niger colonies on the three PDAs was APDA > BPDA > CPDA, and the order of the outer diameters was APDA > CPDA > BPDA. Furthermore, with increasing incubation time, the inner and outer diameters of A. niger colonies on APDA and BPDA, as well as the outer diameter of the colonies on CPDA, showed a steady increase. However, the inner diameter of A. niger on CPDA initially increased and then decreased over time.

[0061] Depend on Figure 1 It can be seen that Aspergillus niger grew best on fresh potato APDA, matured quickly, had dense and thick mycelium, full flora, and contained a large number of black spores; Aspergillus niger inoculated on potato extract powder BPDA grew the slowest, had a shorter flora, and had slightly less black spores than the APDA group; Aspergillus niger grown on potato residue CPDA had a moderate growth rate, but low black spore production and a sparse colony.

[0062] Example 7: Investigation of the Optimal Inoculation Amount and Cultivation Time for Sugar Production by Aspergillus niger in Beet Pomace

[0063] Take appropriate test tubes and weigh 0.1g of beet pulp (free reducing sugar content: 0.122mg / g) and 0.02g of bran (free reducing sugar content: 0.015mg / g) per tube. Autoclave at 121°C for 20 minutes, then dry in a 65°C oven for 20 hours. In a clean room, add the required amounts of nutrient solution, bacterial solution, and PDB culture medium to the beet pulp test tubes (see Table 2). After inoculation, place the test tubes in a 30°C incubator for solid-state fermentation.

[0064] Table 2 Inoculation amount of beet pulp for solid fermentation of Aspergillus niger and addition amount of each liquid

[0065]

[0066] The Aspergillus niger inoculum concentrations set in this experiment were 5%, 10%, 15%, 20%, and 25%, respectively. The reducing sugar content in the beet pulp fermentation products is shown in Table 3. As shown in Table 3, with the increase in microbial content, the reducing sugar content first increased and then decreased, reaching the maximum sugar production at an inoculum concentration of 10%.

[0067] Table 3 Reducing sugar content of beet pulp solid fermented with different inoculum amounts of Aspergillus niger for different days

[0068]

[0069] Draw a reducing sugar standard curve

[0070] Preparation of 3,5-dinitrosalicylic acid (DNS) reagent: Weigh 92.5 g of potassium sodium tartrate and place it in 250 mL of hot water; weigh 3.15 g of DNS, measure 131 mL of sodium hydroxide (2 mol / L), and add them to the previously prepared hot solution; then add 2.5 g each of phenol and sodium sulfite, stir evenly, cool, add water to 500 mL, and store at room temperature in the dark.

[0071] Preparation of 1mg / ml glucose standard solution: Dry the glucose standard at 80℃ for 2 hours. Then accurately weigh 0.1g of dry glucose using an analytical balance. Add appropriate amount of water to fully dissolve the glucose and dilute to 100mL. Make sure to prepare the solution before use.

[0072] Prepare the sample in a 1.5 mL centrifuge tube according to Table 4 and place in a boiling water bath for 5 minutes. Immediately cool to room temperature, dilute to volume, mix, and measure absorbance at 540 nm using a microplate reader.

[0073] Table 4 Preparation of glucose standard test solution

[0074]

[0075] With glucose concentration (mg / mL) as the horizontal axis (x), absorbance (OD 540 ) is the ordinate (y), and a standard curve is drawn. Determination of reducing sugar in samples:

[0076] Add 5 mL of pure water to the fermentation tube and incubate at 60°C for 30 minutes. After 5 minutes, allow to stand, centrifuge at 12,000 rpm for 5 minutes, remove 100 μL of the supernatant, add 400 μL of DNS colorimetric reagent, incubate in a boiling water bath for 5 minutes, cool to room temperature, add 500 μL of water, measure the absorbance at 540 nm, and calculate the reducing sugar content of the sample by applying the standard curve.

[0077] Analysis of results: The time it takes for the strain to ferment beet pulp is of great importance. If the fermentation time is too long, it will not only increase the time cost of actual operation, but may also cause microbial autolysis, a decrease in number, and a decrease in sugar production. If the fermentation time is too short, the microorganisms are still in the growth stage, and the consumption is greater than the output, resulting in insufficient reducing sugar content in the end. The solid fermentation days set in this experiment were 2 days, 4 days, and 6 days (considering the actual operation time cost, the number of days was limited to 6 days). Table 3 shows that the reducing sugar content of the beet pulp fermentation product showed a downward trend in the first 4 days of solid fermentation, while the reducing sugar content increased on the 6th day, reaching the highest sugar content within 6 days.

[0078] In summary, when the inoculation amount of Aspergillus niger liquid was 10% and the solid fermentation days were 6 days, the reducing sugar production of beet pulp was the highest, which was 16.75 mg / g.

[0079] Comparative Example 1: Investigation of the effect of PDB culture medium on the production of reducing sugars from beet pulp fermented by Aspergillus niger

[0080] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0081] In a clean bench, 100 μL of nutrient solution and 20 μL of Aspergillus niger solution (10% inoculum) were added to a test tube of beet pulp and placed in a 30°C constant-temperature incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 1.4597 mg / g. After four days of fermentation, the reducing sugar content in the fermentation broth was 1.9336 mg / g. After six days of fermentation, the reducing sugar content in the fermentation broth was 2.7435 mg / g.

[0082] In summary, if PDB culture medium is not added, Aspergillus niger will grow slowly and very little reducing sugar can be detected during the fermentation process.

[0083] Comparative Example 2: Effects of Nutrient Solution and PDB Culture Solution on Reducing Sugar Production from Beet Pomace by Aspergillus niger

[0084] Take several test tubes, weigh 0.1g of beet pulp and 0.02g of bran in each tube, sterilize them by autoclaving at 121℃ for 20 minutes, and then put them into a 65℃ oven to dry for 20 hours.

[0085] In a clean bench, 20 μL of Aspergillus niger culture (10% inoculum) was added to a test tube of beet pulp and placed in a 30°C constant-temperature incubator for solid-state fermentation. After two days of fermentation, the reducing sugar content in the fermentation broth was 0.6674 mg / g. After four days of fermentation, the reducing sugar content in the fermentation broth was 0.4252 mg / g. After six days of fermentation, the reducing sugar content in the fermentation broth was 0.8881 mg / g.

[0086] In summary, if no nutrient solution and PDB culture medium are added, Aspergillus niger will grow very slowly and very little reducing sugar can be detected during the fermentation process.

[0087] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art will readily appreciate that other variations or modifications may be made based on the above descriptions and concepts. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for producing reducing sugars by fermenting beet pulp with low cost by Aspergillus niger, characterized in that The method comprises the following steps: mixing beet pulp and bran, sterilizing and drying the mixture, adding nutrient solution, black aspergillus solution and PDB culture solution, and performing solid fermentation to produce reducing sugar; the PDB culture solution contains potato flour and glucose.

2. The method according to claim 1, characterized in that The potato flour is one or more of potato residue freeze-dried powder, potato water extract powder or potato extract powder, preferably one or more of potato residue freeze-dried powder and potato water extract powder, more preferably one or more of potato residue freeze-dried powder and fresh potato water extract powder.

3. The method according to claim 1, characterized in that The PDB culture solution contains the following components in parts by weight: 0.1-0.4 parts of potato flour, 0.5-2 parts of glucose, and 30-80 parts of water; preferably, the PDB culture solution contains the following components in parts by weight: 0.2 parts of potato flour, 1 part of glucose, and 50 parts of water.

4. The method according to claim 2, characterized in that The preparation method of the PDB culture medium is as follows: 5 to 20 parts of potatoes are peeled, cut into pieces or crushed, and then mixed with 30 to 80 parts of pure water, heated to boiling water and boiled for 10 to 30 minutes, filtered to obtain the supernatant, and supplemented with 0.5 to 2 parts of anhydrous glucose; The preparation method of the potato water extract powder is as follows: 5 to 20 parts of potatoes are peeled, cut into pieces or crushed, and then mixed with 30 to 80 parts of pure water, heated to boiling water and boiled for 10 to 30 minutes, filtered to obtain the supernatant, and evaporated to remove moisture.

5. The method according to claim 1, characterized in that The Aspergillus niger liquid contains Aspergillus niger.

6. The method according to claim 1, characterized in that The nutrient solution contains yeast powder, peptone, ammonium sulfate, potassium dihydrogen phosphate, magnesium sulfate heptahydrate, manganese sulfate, ferrous sulfate heptahydrate and water.

7. The method according to claim 6, characterized in that The weight composition of the components in the nutrient solution is: 0.5-2 parts of yeast powder, 0.3-0.7 parts of peptone, 1-3 parts of ammonium sulfate, 0.5-2 parts of potassium dihydrogen phosphate, 0.3-0.7 parts of magnesium sulfate heptahydrate, 0.2-0.5 parts of manganese sulfate, 0.03-0.12 parts of ferrous sulfate heptahydrate, and 15-20 parts of water.

8. The method according to claim 1, characterized in that The weight ratios of the components during solid fermentation are: 5-15 parts of beet pulp, 1-4 parts of bran, 5-15 parts of nutrient solution, 1-5 parts of Aspergillus niger liquid, and 4-12 parts of PDB culture liquid; the preferred weight ratios are: 10 parts of beet pulp, 2 parts of bran, 10 parts of nutrient solution, 2 parts of Aspergillus niger liquid, and 8 parts of PDB culture liquid.

9. The method according to claim 1, characterized in that The sterilization operation is: high-pressure sterilization at 120-123° C. for 15-25 minutes; the drying operation is: drying at 60-70° C. for 15-25 hours; the solid fermentation is carried out in a sterile environment; the solid fermentation temperature is 28-32° C., and the solid fermentation time is 2-10 days, preferably 5-7 days.

10. Use of the method according to claim 1 in preparing reducing sugar using beet pulp as raw material.

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