Method for improving utilization rate of residual sugar in lactic acid fermentation through mixed fermentation method and application

Abstract

The invention belongs to the technical field of lactic acid fermentation processes, and particularly relates to a method for improving the utilization rate of residual sugar in lactic acid fermentation through a mixed fermentation method. Comprising the following steps: S1, screening lactic acid bacteria and auxiliary bacteria from a strain library; inoculating lactic acid bacteria into a liquid culture medium containing glucose, xylose, arabinose, mannose and galactose, and culturing; inoculating the auxiliary bacteria into a corresponding culture medium for culturing; s2, inoculating lactic acid bacteria and auxiliary bacteria into the fermentation culture medium according to an inoculation ratio of 3: 1 for fermentation; corn steep liquor and yeast extract are selected as nitrogen sources in the fermentation culture medium, the pH value of the fermentation culture medium is adjusted to 6.0-6.5 after pretreatment, and the total sugar content is 15%-25%; s3, performing fed-batch fermentation, when the residual sugar content is reduced to 5g / L, starting to supplement a mixed sugar solution of glucose and xylose in batches, and maintaining the sugar concentration in a fermentation system; s4, after fermentation is finished, filtering, precipitating and acid pickling are conducted on a fermented product, and then a lactic acid product can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of lactic acid fermentation process, and specifically relates to a method and application for improving the utilization rate of residual sugar in lactic acid fermentation by a mixed culture fermentation method. Background Art

[0002] As an important organic acid, lactic acid has a wide range of applications in many fields such as food, medicine, and chemical industry. Currently, the fermentation method is the main way to produce lactic acid. However, this method generally faces the problem of low utilization rate of residual sugar. During the lactic acid fermentation process, usually a single lactic acid bacterium is used for fermentation. These lactic acid bacteria have limitations in the utilization of sugars in the raw materials, resulting in a large amount of residual sugar remaining in the fermentation broth. This not only causes waste of raw materials and increases production costs, but also brings difficulties to the subsequent separation and purification of lactic acid, greatly hindering the efficient and sustainable development of the lactic acid industry.

[0003] As a rich and inexpensive biomass resource, lignocellulose can be processed by biorefining to obtain various fermentable monosaccharides such as glucose, xylose, arabinose, mannose, and galactose, providing a potential raw material source for lactic acid fermentation. However, wild or ordinary engineering strains are difficult to jointly utilize glucose and non-glucose sugars derived from lignocellulose with a coordinated conversion rate, resulting in a large amount of sugar remaining in the fermentation broth, which limits the efficiency and quality of lactic acid fermentation.

[0004] Therefore, we propose a method and application for improving the utilization rate of residual sugar in lactic acid fermentation by a mixed culture fermentation method. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for improving the utilization rate of residual sugar in lactic acid fermentation by a mixed culture fermentation method to solve the problem of low utilization rate of residual sugar in the existing lactic acid fermentation process.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for improving the utilization rate of residual sugar in lactic acid fermentation by a mixed culture fermentation method, the mixed culture fermentation method includes the following steps:

[0008] S1. Screen lactic acid bacteria and auxiliary bacteria from the existing strain library; inoculate the lactic acid bacteria into a liquid medium containing glucose, xylose, arabinose, mannose, and galactose for cultivation; inoculate the auxiliary bacteria into the corresponding medium for cultivation;

[0009] S2. Inoculate the lactic acid bacteria and auxiliary bacteria into the fermentation medium for fermentation according to an inoculation ratio of 3:1; the fermentation raw material is selected from lignocellulose hydrolysate or molasses, and corn steep liquor and yeast extract are selected as nitrogen sources in the fermentation medium. After pretreatment, adjust its pH value to 6.0 - 6.5, and the total sugar content is 15% - 25%;

[0010] S3. Adopt fed-batch fermentation. When the residual sugar content drops to 5 g / L, start to batchwise add a mixed sugar solution of glucose and xylose to maintain the sugar concentration in the fermentation system; and monitor the ventilation flow rate, pressure value, and pH value during the fermentation process.

[0011] S4. After the fermentation ends, filter, precipitate, and acid-wash the fermentation product to obtain lactic acid products.

[0012] Further, in step S1, the mass ratio of glucose, xylose, arabinose, mannose, and galactose is (4 - 6):3:(1 - 2):(1 - 1):1.

[0013] Further, the culture conditions of the lactic acid bacteria in step S1 are: temperature is 37 °C, pH value is 6.0, and microaerobic culture for 18 hours.

[0014] Further, the auxiliary bacteria are one of yeast or bacillus.

[0015] Further, yeast is inoculated into wort medium for culture, and the culture conditions are: culture at 30 °C under aerobic conditions for 24 hours; bacillus is inoculated into nutrient broth medium for culture, and the culture conditions are culture at 32 °C for 20 hours.

[0016] Further, in step S2, the sugar clear liquid, corn steep liquor solution, and yeast extract are added to the fermentation tank according to the volume ratio of sugar clear liquid∶corn steep liquor solution∶yeast extract = 100∶(0.015 - 0.025)∶(0.004 - 0.013). The total sugar content of the sugar clear liquid is (210 - 240) g / L, the DE value is (92% - 100%), the DX value is (90% - 100%), and in the corn steep liquor solution: dry matter ≥ 40%, protein ≥ 45%, acidity ≤ 14%.

[0017] Further, the fermentation conditions in step S2 are: fermentation temperature is 40 - 50 °C, pH value is 5.0 - 7.0, fermentation time is 48 - 72 hours, and the rotation speed is set at 100 - 300 revolutions per minute during the fermentation process.

[0018] Further, in step S3, sterile air needs to be continuously introduced, the ventilation flow rate is 1.5 cubic meters per hour per ton of liquid material, and the pressure in the fermentation tank is maintained at 0.6 MPa; the pH value in the fermentation tank is controlled at 6.0 - 7.0.

[0019] Further, the specific steps of step S4 are to first filter to remove bacteria and insoluble impurities, then add sodium carbonate step by step to the fermentation broth for precipitation replacement, pass the obtained soluble lactate solution through an anion exchange column for ion exchange, and finally acid-wash the anion exchange column adsorbed with lactate ions to obtain lactic acid products.

[0020] Advantages of the present invention:

[0021] 1. By screening lactic acid bacteria that are resistant to high sugar and can efficiently utilize various sugars, as well as auxiliary bacteria with the ability to promote sugar conversion for mixed bacteria fermentation, the present invention can fully utilize various sugars in the raw materials and significantly improve the residual sugar utilization rate. Experiments show that compared with single lactic acid bacteria fermentation, the residual sugar utilization rate can be increased by 30%-50% through mixed bacteria fermentation.

[0022] 2. The optimized fermentation process parameters, suitable fermentation raw materials and pretreatment methods of the present invention provide a good environment for the growth and metabolism of microorganisms, promote the production of lactic acid, and significantly increase the lactic acid yield. Under the same fermentation conditions, the lactic acid yield of mixed bacteria fermentation is 20%-35% higher than that of single lactic acid bacteria fermentation.

[0023] 3. By improving the residual sugar utilization rate and increasing the lactic acid yield, the present invention reduces the waste of raw materials and subsequent treatment costs. At the same time, the reasonable treatment of fermentation residues also reduces the environmental protection costs, comprehensively reducing the total cost of lactic acid production. Specific embodiments

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0025] A method for improving the residual sugar utilization rate in lactic acid fermentation by a mixed bacteria fermentation method, the mixed bacteria fermentation method comprising the following steps:

[0026] S1. Screening and culturing specific strains

[0027] Screening lactic acid bacteria that are resistant to high sugar and can efficiently utilize various sugars: From the existing strain library, through screening in a high sugar environment and detection of the utilization ability of different sugars, lactic acid bacteria strains that can grow well under high sugar concentration and can efficiently utilize various sugars such as glucose, xylose, arabinose, mannose, and galactose are isolated. The screened lactic acid bacteria strains have good utilization ability for xylose and glucose.

[0028] Screening auxiliary bacteria with the ability to promote sugar conversion: Look for microorganisms with specific enzyme activity or metabolites that can promote the conversion of sugars into lactic acid, such as certain yeasts or Bacillus. These auxiliary bacteria can secrete substances that help decompose complex sugars or promote the metabolism of lactic acid bacteria. For example, yeast can hydrolyze disaccharides into glucose to promote the growth of lactic acid bacteria. The screened lactic acid bacteria and auxiliary bacteria are expanded and cultured separately. The lactic acid bacteria are inoculated into a liquid culture medium rich in various sugars (such as glucose, xylose, arabinose, mannose and galactose mixed in a certain proportion), and aerobic or microaerobic culture is carried out for a certain period of time (such as 12-24 hours) at a suitable temperature (usually 30-40°C, such as 37°C) and pH value (generally 5.5-6.5, such as 6.0) to make the lactic acid bacteria proliferate in large quantities. The auxiliary bacteria are inoculated into a culture medium suitable for their growth, and the culture conditions are controlled according to their characteristics, such as yeast in a sugar-containing culture medium, 28-32°C, and cultured under aerobic conditions for 18-30 hours.

[0029] S2. Optimize fermentation process parameters

[0030] The optimal inoculation ratio of lactic acid bacteria and auxiliary bacteria was explored through experiments. Lactic acid bacteria and auxiliary bacteria were inoculated into the fermentation medium according to different volume ratios (such as 1:1, 2:1, 3:1, etc.), and indicators such as residual sugar content, lactic acid production and fermentation time were monitored during the fermentation process. The results showed that when the inoculation ratio of lactic acid bacteria and auxiliary bacteria was 3:1, the residual sugar utilization rate was high and the lactic acid production was considerable.

[0031] Adjust the fermentation temperature and pH value: Study the effects of different fermentation temperatures (such as 40-50°C) and pH values ​​(such as 5.0-7.0) on mixed fermentation. Set up multiple experimental groups, control different combinations of temperature and pH values, and regularly test the residual sugar and lactic acid content in the fermentation broth. It was determined that the mixed fermentation effect was best at 45°C and a pH value of 6.0. At this time, the residual sugar can be more fully utilized and the lactic acid production rate is faster. During the fermentation process, an automated control system is used to monitor and adjust the temperature and pH value in real time to ensure the stability of the fermentation environment.

[0032] Control the fermentation time and stirring speed: determine the optimal fermentation time, regularly detect the residual sugar and lactic acid content in the fermentation broth, draw a fermentation curve, and observe the changes in residual sugar utilization and lactic acid production over time. Generally speaking, a fermentation time of 48-72 hours is more appropriate. For example, at 60 hours, the residual sugar utilization rate is high and the lactic acid production reaches a relatively high level. At the same time, set different stirring speeds (such as 100-300 rpm) for experiments to study their effects on the fermentation effect. It was found that when the stirring speed was 200 rpm, the microorganisms in the fermentation broth could fully contact with nutrients, promoting the utilization of residual sugar and the production of lactic acid.

[0033] Select appropriate fermentation feedstock and pretreatment method

[0034] Select raw materials rich in various sugars: Select materials rich in various sugars such as lignocellulose hydrolysate and molasses as fermentation raw materials. For example, lignocellulose hydrolysate contains various sugars such as glucose, xylose, and arabinose, providing a rich carbon source for mixed culture fermentation. Pretreat the raw materials to improve the availability of sugars. For lignocellulose hydrolysate, use methods such as filtration and centrifugation to remove impurities and adjust its pH value to an appropriate range (such as 6.0 - 6.5). For molasses, dilute it to an appropriate sugar concentration (such as the total sugar content is 15% - 25%), and remove substances that may inhibit the growth of microorganisms.

[0035] Add nutrients: Add appropriate amounts of nitrogen sources (such as corn steep liquor, yeast extract, etc.), phosphorus sources (such as potassium dihydrogen phosphate, etc.), as well as vitamins and minerals and other nutrients to the fermentation medium to meet the growth and metabolic needs of microorganisms. For example, add them to the fermenter according to the volume ratio of sugar syrup∶corn steep liquor solution∶yeast extract = 100∶0.015 - 0.025∶0.004 - 0.013. The total sugar content of the sugar syrup is 210 - 240 g / L, the DE value is 92% - 100%, the DX value is 90% - 100%. In the corn steep liquor solution: dry matter ≥ 40%, protein ≥ 45%, acidity ≤ 14%.

[0036] S3. Fermentation process control

[0037] Adopt fed-batch fermentation: During the fermentation process, according to the change of residual sugar content, timely supplement sugar raw materials to the fermenter. For example, when the residual sugar content drops to a certain level (such as 5 g / L), start to batch add sugars such as glucose and xylose to maintain a certain sugar concentration in the fermentation system, ensure the continuous growth and metabolism of microorganisms, and improve the utilization rate of residual sugar. By monitoring the dissolved oxygen content in the fermentation broth, control the ventilation volume. Generally, adopt the method of continuously introducing sterile air, and the ventilation flow rate is 0.75 - 4 cubic meters per hour per ton of liquid material, maintaining a certain pressure in the fermenter (such as 0.4 - 0.8 MPa) to meet the oxygen demand of microorganisms and promote their growth and metabolism. At the same time, make the fermentation broth evenly mixed by stirring to ensure full contact between microorganisms and nutrients.

[0038] Monitor and regulate fermentation parameters: Use sensors to real-time monitor parameters such as temperature, pH value, residual sugar content, lactic acid content, and dissolved oxygen during the fermentation process, and transmit the data to the control system. The control system automatically adjusts the heating, cooling devices, and acid-base addition devices according to the preset parameter range to maintain the stability of fermentation temperature and pH value. When abnormal changes occur in the residual sugar content or lactic acid content, timely adjust the feeding strategy or fermentation conditions such as ventilation volume.

[0039] S4. Post-treatment process

[0040] Separation and purification of lactic acid: After the fermentation is completed, the fermentation broth is treated by a suitable method to separate and purify lactic acid. Specifically: First, the bacteria and insoluble impurities in the fermentation broth are removed by filtration, and then carbonates are added step by step to the lactic acid fermentation broth for precipitation replacement to obtain a soluble lactate solution and a precipitate; the obtained soluble lactate solution is subjected to ion exchange through an anion exchange column to obtain an anion exchange column adsorbed with lactate ions and ion exchange waste liquid; the anion exchange column adsorbed with lactate ions is pickled to obtain lactic acid products.

[0041] Treatment of fermentation residue: The fermentation residue is reasonably treated to recover useful substances therein or to perform environmental protection disposal. The fermentation residue may contain unutilized sugars, microbial cells, etc. The sugars or proteins, etc. therein can be extracted through further treatment and used for other industrial production or feed processing, etc. For the part that cannot be recycled, it is treated in an environmentally friendly way, such as biodegradation or incineration for power generation, etc., to reduce the impact on the environment.

[0042] Example 1

[0043] S1. Strain screening and cultivation: Lactobacillus and yeast are screened from the existing strain library. The Lactobacillus is inoculated into a liquid medium containing glucose, xylose, arabinose, mannose and galactose (mass ratio 5:3:2:1:1), and microaerobically cultivated at 37 °C and a pH value of 6.0 for 18 hours. The yeast is inoculated into a wort medium and cultivated at 30 °C under aerobic conditions for 24 hours.

[0044] S2. Determination of fermentation process parameters: The fermentation temperature is set at 42 °C, the pH value is 6.2, the inoculation ratio of Lactobacillus and yeast is 3:1, the fermentation time is 50 hours, and the stirring speed is 220 revolutions per minute. The fermentation raw material is selected as the lignocellulose hydrolysate. After pretreatment, its pH value is adjusted to 6.2 and the total sugar content is 20%. Nutrients such as corn steep liquor, yeast extract, potassium dihydrogen phosphate, etc. are added to the fermentation medium.

[0045] S3. Fermentation process control: Fed-batch fermentation is adopted. When the residual sugar content drops to 6 g / L, a mixed sugar solution of glucose and xylose is added in batches. Sterile air is continuously introduced, and the ventilation flow rate is 1.5 cubic meters per hour per ton of liquid material, and the pressure in the fermentation tank is maintained at 0.6 MPa. The fermentation parameters are monitored in real time, and the temperature, pH value and ventilation volume are adjusted as needed.

[0046] S4. Post-treatment: After fermentation, the cells and insoluble impurities are first removed by filtration, and then sodium carbonate is added stepwise to the fermentation broth for precipitation replacement. The resulting soluble lactate solution is subjected to ion exchange through an anion exchange column. Finally, the anion exchange column adsorbed with lactate ions is pickled to obtain lactic acid products. The fermentation residue is treated to extract the protein for feed processing.

[0047] Results: The residual sugar utilization rate reached 75%, and the lactic acid production was 123 g / L. Compared with single lactic acid bacteria fermentation, the residual sugar utilization rate increased by 35%, and the lactic acid production increased by 23%.

[0048] Example 2

[0049] S1. Strain screening and cultivation: Lactobacillus and Bacillus are selected from the existing strain bank. Lactobacillus is aerobically cultivated in a medium containing various sugars (the mass ratio of glucose, xylose, arabinose, mannose and galactose is 4:3:2:2:1) at 35 °C and a pH value of 6.0 for 15 hours. Bacillus is inoculated into a nutrient broth medium and cultivated at 32 °C for 20 hours.

[0050] S2. Determination of fermentation process parameters: The fermentation temperature is set at 44 °C, the pH value is 6.0, the inoculation ratio of Lactobacillus and Bacillus is 3:1, the fermentation time is 55 hours, and the stirring speed is 200 revolutions per minute. The fermentation raw material is molasses, diluted to a total sugar content of 22%, and the pH value is adjusted to 6.0. Appropriate amounts of nitrogen source, phosphorus source and vitamins and other nutrients are added to the fermentation medium.

[0051] S3. Fermentation process control: When the residual sugar content drops to 5 g / L, sugar raw materials are supplemented. The ventilation flow rate is 2.0 cubic meters per hour per ton of liquid material, and the pressure is maintained at 0.5 MPa. The fermentation parameters are monitored and regulated in real time.

[0052] S4. Post-treatment: After fermentation, the cells and insoluble impurities are first removed by filtration, and then sodium carbonate is added stepwise to the fermentation broth for precipitation replacement. The resulting soluble lactate solution is subjected to ion exchange through an anion exchange column. Finally, the anion exchange column adsorbed with lactate ions is pickled to obtain lactic acid products. The fermentation residue is treated to extract the protein for feed processing.

[0053] Results: The residual sugar utilization rate reached 78%, and the lactic acid production was 125 g / L. Compared with single lactic acid bacteria fermentation, the residual sugar utilization rate increased by 40%, and the lactic acid production increased by 25%.

[0054] Comparative Example 1

[0055] S1. Strain screening and cultivation: Select lactic acid bacteria from the existing strain library. Aerobically cultivate the lactic acid bacteria in a medium containing various sugars (the mass ratio of glucose, xylose, arabinose, mannose, and galactose is 4:3:2:2:1) at 35 °C and a pH value of 6.0 for 15 hours.

[0056] S2. Determination of fermentation process parameters: Set the fermentation temperature at 44 °C, the pH value at 6.0, the fermentation time at 55 hours, and the stirring speed at 200 revolutions per minute. Select the lignocellulose hydrolysate as the raw material, adjust the total sugar content to 18% after pretreatment, and the pH value to 6.1. Add rich nutrients to the fermentation medium.

[0057] S3. Fermentation process control: When the residual sugar content drops to 5 g / L, add sugar raw materials. Select the lignocellulose hydrolysate as the raw material, adjust the total sugar content to 18% after pretreatment, and the pH value to 6.1. Add rich nutrients to the fermentation medium.

[0058] S4. Post-treatment: After fermentation, first filter to remove the bacteria and insoluble impurities, then add sodium carbonate step by step to the fermentation broth for precipitation replacement. Pass the obtained soluble lactate solution through an anion exchange column for ion exchange, and finally perform acid washing on the anion exchange column adsorbed with lactate ions to obtain lactic acid products. Treat the fermentation residue and extract the protein therein for feed processing.

[0059] Result: The residual sugar utilization rate reaches 55%, and the lactic acid production is 100 g / L.

[0060] It can be seen from the above examples that the mixed bacteria fermentation method of the present invention can significantly improve the utilization rate of residual sugar in lactic acid fermentation, increase lactic acid production, reduce production costs, and has good application prospects.

[0061] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0062] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation, characterized in that: The mixed bacteria fermentation method comprises the following steps: S1. Screening lactic acid bacteria and auxiliary bacteria from an existing bacterial strain library; inoculating the lactic acid bacteria into a liquid culture medium containing glucose, xylose, arabinose, mannose and galactose for cultivation; inoculating the auxiliary bacteria into a corresponding culture medium for cultivation; S2, inoculating lactic acid bacteria and auxiliary bacteria into a fermentation medium at an inoculation ratio of 3:1 for fermentation; using lignocellulose hydrolyzate or molasses as the fermentation raw material, using corn steep liquor and yeast extract as nitrogen sources in the fermentation medium, adjusting the pH value to 6.0-6.5 after pretreatment, and adjusting the total sugar content to 15%-25%; S3. Batch fed fermentation was adopted. When the residual sugar content dropped to 5 g / L, a mixed sugar solution of glucose and xylose was added in batches to maintain the sugar concentration in the fermentation system; and the ventilation flow, pressure value and pH value during the fermentation process were monitored. S4. After the fermentation is completed, the fermented product is filtered, precipitated and pickled to obtain the lactic acid product.

2. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: In step S1, the mass ratio of glucose, xylose, arabinose, mannose and galactose is (4-6):3:(1-2):(1-1):

1.

3. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: The culture conditions of lactic acid bacteria in step S1 are: temperature of 37° C., pH of 6.0, and microaerobic culture for 18 hours.

4. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: The auxiliary bacteria is one of yeast or bacillus.

5. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 4, characterized in that: The yeast was inoculated into the malt extract medium and cultured at 30°C under aerobic conditions for 24 hours; the Bacillus was inoculated into the nutrient broth medium and cultured at 32°C for 20 hours.

6. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: In step S2, a sugar solution, a corn syrup solution and a yeast extract are added to a fermentation tank in a volume ratio of sugar solution: corn syrup solution: yeast extract = 100: (0.015-0.025): (0.004-0.013), wherein the total sugar content of the sugar solution is (210-240) g / L, the DE value is (92%-100%), and the DX value is (90%-100%). In the corn syrup solution, dry matter is ≥40%, protein is ≥45%, and acidity is ≤14%.

7. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: The fermentation conditions in step S2 are: fermentation temperature of 40-50° C., pH value of 5.0-7.0, fermentation time of 48-72 hours, and the rotation speed during the fermentation process is set at 100-300 rpm.

8. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: In step S3, sterile air needs to be continuously introduced, and the ventilation flow rate is 1.5 cubic meters per hour per ton of liquid feed, and the pressure in the fermentation tank is maintained at 0.6 MPa; the pH value in the fermentation tank is controlled at 6.0-7.

0.

9. The method for improving the utilization rate of residual sugar in lactic acid fermentation by mixed bacteria fermentation according to claim 1, characterized in that: The specific steps of step S4 are to first filter and remove the bacteria and insoluble impurities, then add sodium carbonate to the fermentation broth step by step for precipitation replacement, pass the obtained soluble lactate solution through an anion exchange column for ion exchange, and finally acid wash the anion exchange column that adsorbs lactate ions to obtain a lactic acid product.