Method for stably producing L-lactic acid through acidic fermentation

Abstract

The invention discloses a method for stably producing L-lactic acid through acidic fermentation, which comprises the following steps: S1, carrying out liquefaction and pre-saccharification treatment on corn starch, and adding pre-treated corncob residues to obtain pre-fermented feed liquid; s2, taking bacillus coagulans as a fermentation strain, and inoculating the fermentation strain into the pre-fermentation material liquid in a gradual expansion manner; s3, fermenting after inoculating, and controlling the pH value of the fermentation material liquid to be 5.1 + / -0.1; and S4, after fermentation, carrying out plate frame filtration and MVR evaporation to obtain the lactic acid fermentation broth. According to the method for stably producing L-lactic acid through acidic fermentation, the pH difference of fermentation feed liquid at different parts can be effectively reduced, the uniformity and consistency of the fermentation feed liquid are guaranteed, a good growth and acid production environment is provided for strains, the fermentation period is effectively shortened, and the acid production capacity is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lactic acid production, in particular to a method for stably producing L-lactic acid by acid fermentation. BACKGROUND

[0002] L-lactic acid, as an important organic acid, has a wide range of applications in food, medicine, chemical industry, biodegradable materials and other fields.

[0003] Biological fermentation is the most commonly used method for producing L-lactic acid, which has high dynamics and coupling. In order to ensure the fermentation quality of lactic acid, the pH value of the fermentation broth needs to be precisely controlled to maintain high activity and stability of lactic acid bacteria. During the fermentation process, the pH value of the fermentation broth gradually decreases, and an alkaline neutralizing agent needs to be added to maintain the stability of the pH value. However, as the fermentation scale expands, the material exchange delay of the fermentation broth increases, making it difficult to detect the dynamic changes of the pH value in the fermentation system in real time and accurately. At the same time, the alkaline neutralizing agent is also difficult to adjust in a timely and effective manner, resulting in the formation of a low-pH acidic environment in local areas, which inhibits the activity of the bacterial strain and even causes the bacterial strain to become inactive, seriously affecting the fermentation efficiency and the yield of L-lactic acid.

[0004] Therefore, it is a key problem in the current lactic acid fermentation technology field to develop a production method that does not require a large amount of added neutralizing agent and can achieve stable control of the pH value of the fermentation broth. SUMMARY

[0005] To this end, the present application provides a method for stably producing L-lactic acid by acid fermentation, which can effectively reduce the pH difference of the fermentation broth in different parts, ensure the uniformity and consistency of the fermentation broth, provide good growth and acid production conditions for the bacterial strain, effectively shorten the fermentation period, and greatly improve the acid production capacity.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A method for stably producing L-lactic acid by acid fermentation, comprising the following steps:

[0008] S1. Liquefy and pre-saccharify corn starch to obtain a pre-saccharification solution, add pretreated corn cob residues to the pre-saccharification solution, stir uniformly, and then sterilize to obtain a pre-fermentation broth;

[0009] S2. Use Bacillus coagulans as the fermentation strain, prepare the initial strain in a shake flask, and inoculate it in the fermentation tank in a step-by-step expansion manner, with an inoculation amount of 10-15% of the volume of the pre-fermentation broth in the fermentation tank;

[0010] S3. After inoculation of the fermenter, sterile air is introduced, the pressure and temperature are adjusted, and fermentation is carried out; when the pH of the fermentation broth is reduced to 5.1±0.1, the neutralizing agent is added, the pH of the fermentation broth is maintained at 5.1±0.1, and the fermentation is continued;

[0011] S4. Fermentation is carried out until the glucose concentration in the fermentation broth is reduced to 0, aeration is stopped, and the fermentation is continued for 1.5-2.5 h, the fermentation is completed, plate and frame filtration and MVR evaporation are carried out, the lactic acid fermentation liquor is obtained, and then acidolysis, directional adsorption extraction and molecular distillation are carried out to obtain the finished lactic acid.

[0012] Further, the pretreated corncob residue is prepared by treating the corncob residue with amylase and then doping with organic coated calcium carbonate.

[0013] Further, the coating material of the organic coated calcium carbonate is chitosan.

[0014] Further, the preparation of the organic coated calcium carbonate comprises the following steps: surface treatment of calcium carbonate with stearic acid, then placing the surface treated calcium carbonate in a chitosan solution with a mass fraction of 1-2% at 50-60°C, stirring uniformly, filtering, drying, and sieving to obtain the organic coated calcium carbonate.

[0015] Further, the preparation method of the pretreated corncob residue is as follows:

[0016] A1. After drying, the corncob residue is crushed and sieved through a 40-60 mesh screen, then heated and stirred in an alkali solution for 0.5-1 h, filtered, and the filter residue is subjected to enzymatic hydrolysis with a cellulase solution to obtain an enzymatic hydrolysate;

[0017] A2. Organic coated calcium carbonate and sodium dodecyl sulfate are added to the enzymatic hydrolysate, stirred and then allowed to stand, filtered, dried, and sieved through an 8-20 mesh screen to obtain the pretreated corncob residue.

[0018] Further, the amount of organic coated calcium carbonate added in step A2 is 3-5% of the mass of the corncob residue in the enzymatic hydrolysate.

[0019] Further, the alkali solution is one or a mixture of both of sodium hydroxide solution and potassium hydroxide solution, and the mass fraction of the alkali solution is 1-2%.

[0020] Further, during the liquefaction process, the corn starch is adjusted to a corn starch milk with a dry matter mass fraction of 27-30%, amylase is added, jet liquefaction is carried out, the jet temperature is controlled at 108-110°C, high temperature is maintained for 4-5 min, then the temperature is maintained at 90-100°C and the pH value is maintained at 5.0-5.3 for 20-50 min to obtain a liquefied sugar solution.

[0021] Further, in the pre-saccharification process, the temperature is 60-62 DEG C, the pH value is 4.2-4.5, the amount of saccharifying enzyme added is 0.35-0.40 mg / g of total sugar in the liquefied sugar solution, and the saccharification time is 3-5 h.

[0022] Further, after the fermentation tank is inoculated, the fermentation temperature is controlled to be 50-52 DEG C, the pressure is 0.02 MPa, the aeration amount is 0.1-0.12 vvm, and the natural pH is used for fermentation, when the fermentation broth pH is reduced to 5.1±0.1, 20-30% content of calcium hydroxide solution is added, and the fermentation is maintained in the pH range, when the fermentation broth OD 620 reaches 14 or more, at this time, the fermentation broth in the fermentation tank can be used as a strain, inoculated into a fermentation tank with the same volume or a larger volume, and the inoculation amount is 10-15% of the pre-fermentation broth volume in the fermentation tank.

[0023] The technical scheme of the present application achieves the following beneficial technical effects:

[0024] 1. For the problems of local environmental imbalance, reduced or inactivated strain activity, etc. caused by the difficulty in dynamic detection of pH value and the difficulty in controlling the added neutralizing agent in the large-scale fermentation process, the present application uses agricultural waste corn cob residue as a carrier material, and modifies it by doping with organic coated calcium carbonate to obtain a pretreated corn cob residue with synergistic effect, which is applied to the L-lactic acid fermentation system, can quickly and accurately control the pH value of the fermentation broth in the local area, reduce the pH value difference at different positions in the tank, effectively improve the strain activity and fermentation quality, and realize the efficient large-scale production of L-lactic acid.

[0025] 2. The fibrous structure of the corn cob residue has a high specific surface area, which can provide favorable conditions for the uniform attachment of calcium carbonate, and chitosan is a natural polysaccharide macromolecule, which has structural similarity and good compatibility with cellulose in the corn cob residue, the organic coating layer formed by the combination of chitosan and calcium carbonate can not only improve the adhesion strength of calcium carbonate in the corn cob residue, but also realize the uniform distribution of calcium carbonate in the fermentation broth, avoid the uneven pH buffering capacity caused by local aggregation, and realize the micro-area accurate control of the fermentation broth pH.

[0026] 3. The solubility of chitosan is special, the solubility of chitosan is higher in the solution with stronger acidity (lower pH value), the local area with too low pH value in the fermentation broth can make chitosan dissolve quickly, release the internal calcium carbonate, neutralize the acidic substances in the fermentation broth, thereby the local fermentation broth with too low pH value is controlled in a targeted manner, in addition, the calcium carbonate can produce carbon dioxide gas in the acidic liquid, the bubbles can drive the surrounding liquid to move in the rising process, which is helpful to improve the flowability of the surrounding substances, reduce the mass transfer resistance and pH gradient in the fermentation tank, therefore, the local too low pH value in the fermentation broth can be effectively controlled, the inactivation and deactivation of the bacterial species are avoided, and the fermentation speed and acid production capacity of the lactic acid bacteria are significantly improved. DETAILED DESCRIPTION

[0027] Example 1

[0028] An acid fermentation method for stably producing L-lactic acid, comprising the following steps:

[0029] S1. corn starch emulsion with a mass fraction of 28% dry matter is prepared, 0.14 mg / g corn starch of high-temperature-resistant alpha-amylase is added, jet liquefaction is carried out, the jet temperature is controlled to be 110 DEG C, after maintaining for 4 min, the temperature is reduced to 95 DEG C, under the condition that the pH value is 5.2, it is maintained for 30 min, then the liquefied sugar solution is obtained, then the liquefied sugar solution is subjected to pre-saccharification treatment, the pre-saccharification temperature is 61 DEG C, the pH value is 4.3, the addition amount of saccharifying enzyme is 0.38 mg / g of the total sugar mass in the liquefied sugar solution, and the saccharification time is 4 h, then a pre-saccharification solution is obtained, the pretreated corncob residues are added to the pre-saccharification solution, the mass ratio of the pre-saccharification solution to the pretreated corncob residues is 20:1, after uniform stirring, sterilization treatment is carried out, the sterilization mode is 110 DEG C steam heating for 20 min, and then a pre-fermentation broth is obtained;

[0030] S2. Bacillus coagulans is used as a fermentation strain, the initial strain is prepared in a shake flask, the culture medium comprises the following substances: sugar water with a total sugar content of 220 g / L, yeast powder (as a nitrogen source, the carbon-nitrogen ratio of the sugar water to the yeast powder is 19:1), 2.0 g / L of diammonium citrate, 2.0 g / L of K2HPO4, 0.2 g / L of MgSO4·7H2O, 0.05 g / L of MnSO4·H2O, 0.03 g / L of NaCl, 0.01 g / L of FeSO4·7H2O, 5.0 g / L of sodium acetate trihydrate and 1.0 mL / L of Tween, and is inoculated in a fermentation tank in a step-by-step expanding manner, and the inoculation amount is 10-15% of the volume of the pre-fermentation broth in the fermentation tank;

[0031] S3. After inoculation in the fermenter, control the fermentation temperature at 51℃, the pressure at 0.02MPa, and the aeration rate at 0.11vvm. Fermentation is carried out at natural pH. When the pH of the fermentation solution drops to 5.1±0.1, add a 25% calcium hydroxide solution to maintain fermentation within this pH range and continue fermentation. When the pH of the fermentation solution drops to OD... 620 When the concentration reaches 14 or higher, the liquid in the fermenter can be used as a starter culture and inoculated into a fermenter of the same or larger volume.

[0032] S4. Ferment until the glucose concentration in the fermentation liquid drops to 0, stop aeration, continue fermentation for 2 hours, then fermentation ends. Add 25% calcium hydroxide solution to adjust the pH to 9, perform plate and frame filtration and MVR evaporation to obtain lactic acid fermentation broth, and then perform acid hydrolysis, directional adsorption extraction and molecular distillation to obtain the finished lactic acid.

[0033] The preparation of organically coated calcium carbonate includes the following steps: surface treatment of calcium carbonate with 1% stearic acid by mass, then placing the surface-treated calcium carbonate in a 1.5% chitosan solution at 55°C, stirring evenly, filtering, drying, and sieving to obtain organically coated calcium carbonate.

[0034] The preparation method of pretreated corn cob residue is as follows:

[0035] A1. After drying and crushing the corn cob residue, pass it through a 40-mesh sieve, then place it in a 1% sodium hydroxide solution at 50℃ and stir for 1 hour. Filter the residue and enzymatically hydrolyze it with cellulase solution at 50℃ and pH 5.0 for 12 hours. The amount of cellulase used is 20 FPU / g of the residue. After the enzymatic hydrolysis is completed, the enzymatic hydrolysate is obtained.

[0036] A2. Add organically coated calcium carbonate and sodium dodecyl sulfate to the enzymatic hydrolysate. The amount of organically coated calcium carbonate added is 4% of the mass of the corn cob residue in the enzymatic hydrolysate, and the amount of sodium dodecyl sulfate added is 0.5% of the mass of the enzymatic hydrolysate. After stirring, let stand, filter, dry, and pass through an 8-mesh sieve to obtain pretreated corn cob residue.

[0037] Example 2

[0038] A method for the stable production of L-lactic acid by acidic fermentation includes the following steps:

[0039] S1. Prepare a corn starch emulsion with a mass fraction of 27% dry matter, add 0.14 mg / g corn starch of high-temperature-resistant alpha-amylase, perform jet liquefaction, control the jet temperature to be 108℃, maintain for 5 min, then reduce the temperature to 90℃, maintain for 50 min at a pH value of 5.0, and obtain a liquefied sugar solution, then perform pre-saccharification treatment on the liquefied sugar solution, the pre-saccharification temperature is 60℃, the pH value is 4.2, the amount of saccharifying enzyme added is 0.35 mg / g of the total sugar mass in the liquefied sugar solution, and the saccharification time is 5 h, to obtain a pre-saccharification solution, then add pretreated corncob residues to the pre-saccharification solution, the mass ratio of the pre-saccharification solution to the pretreated corncob residues is 100:4, uniformly stir, and sterilize by steam heating at 105℃ for 40 min to obtain a pre-fermentation feed liquid;

[0040] S2. Use Bacillus coagulans as the fermentation strain, prepare the initial strain in a shake flask, and the culture medium comprises the following substances: sugar water with a total sugar content of 210 g / L, yeast powder (as a nitrogen source, the carbon-nitrogen ratio of the sugar water and the yeast powder is 19:1), 2.0 g / L of diammonium citrate, 2.0 g / L of K2HPO4, 0.2 g / L of MgSO4·7H2O, 0.05 g / L of MnSO4·H2O, 0.03 g / L of NaCl, 0.01 g / L of FeSO4·7H2O, 5.0 g / L of sodium acetate trihydrate, and 1.0 mL / L of Tween, inoculate the fermentation tank in a step-by-step expansion manner, and the inoculation amount is 10% of the volume of the pre-fermentation feed liquid in the fermentation tank;

[0041] S3. After inoculation of the fermentation tank, control the fermentation temperature to be 50℃, the pressure to be 0.02 MPa, the aeration amount to be 0.1 VVM, and the natural pH to perform fermentation, when the pH of the fermentation feed liquid is reduced to 5.1, add 20-30% content of calcium hydroxide solution, maintain the pH in the range, and continue to ferment; when the OD 620 of the fermentation feed liquid is greater than 14, the feed liquid in the fermentation tank at this time can be used as a strain to inoculate a fermentation tank with the same volume or a larger volume;

[0042] S4. Ferment until the glucose concentration in the fermentation feed liquid is reduced to 0, stop aeration, continue to ferment for 1.5 h, and then stop the fermentation, add 20% content of calcium hydroxide solution to adjust the pH to 8, perform plate and frame filtration and MVR evaporation to obtain a lactic acid fermentation liquid, and then perform acidolysis, directional adsorption extraction, and molecular distillation to obtain finished lactic acid;

[0043] The preparation of the organic-coated calcium carbonate includes the following contents: 1% stearic acid by mass of calcium carbonate is used for surface treatment of the calcium carbonate, then the surface-treated calcium carbonate is placed in a 2% chitosan solution by mass at 50℃, uniformly stirred, filtered, dried, and sieved to obtain the organic-coated calcium carbonate;

[0044] The preparation method of the pretreated corncob residue is as follows:

[0045] A1. After drying the corncob residue, it is crushed and passed through a 60-mesh screen, and then placed in a 1% potassium hydroxide solution at 50°C, stirred for 1 hour, filtered, and the filter residue is subjected to enzymatic hydrolysis at 45°C and pH 5.2 using a cellulase solution for 15 hours, with the cellulase dosage being 25 FPU / g of filter residue. After the enzymatic hydrolysis is completed, an enzymatic hydrolysate is obtained;

[0046] A2. Organic coated calcium carbonate and sodium dodecyl sulfate are added to the enzymatic hydrolysate, with the addition amount of organic coated calcium carbonate being 3% of the mass of the corncob residue in the enzymatic hydrolysate, and the addition amount of sodium dodecyl sulfate being 0.4% of the mass of the enzymatic hydrolysate. After stirring, it is allowed to stand, filtered, dried, and passed through a 16-mesh screen to obtain pretreated corncob residue.

[0047] Example 3

[0048] A method for stably producing L-lactic acid by acid fermentation, comprising the following steps:

[0049] S1. A corn starch emulsion with a dry matter mass fraction of 30% is prepared, and 0.14 mg / g of corn starch of high-temperature-resistant α-amylase is added for jet liquefaction, with the jet temperature being controlled at 110°C for 4 min, and then the temperature is reduced to 100°C. The liquefied sugar solution is obtained by maintaining the pH value at 5.3 for 20 min. Then the liquefied sugar solution is subjected to pre-saccharification treatment, with the pre-saccharification temperature being 62°C and the pH value being 4.2. The saccharifying enzyme is added in an amount of 0.40 mg / g of the total sugar mass in the liquefied sugar solution, and the saccharification time is 3 h to obtain a pre-saccharification solution. The pretreated corncob residue is added to the pre-saccharification solution, and the mass ratio of the pre-saccharification solution to the pretreated corncob residue is 100:6. After uniform stirring, sterilization treatment is performed by steam heating at 110°C for 20 min to obtain a pre-fermentation feed solution.

[0050] S2. Bacillus coagulans is used as the fermentation strain, and the initial strain is prepared in a shake flask. The culture medium includes the following substances: sugar water with a total sugar content of 230 g / L, yeast powder (as a nitrogen source, with a carbon-nitrogen ratio of 19:1 between the sugar water and the yeast powder), 2.0 g / L of diammonium citrate, 2.0 g / L of K2HPO4, 0.2 g / L of MgSO4·7H2O, 0.05 g / L of MnSO4·H2O, 0.03 g / L of NaCl, 0.01 g / L of FeSO4·7H2O, 5.0 g / L of sodium acetate trihydrate, and 1.0 mL / L of Tween. The strain is inoculated into a fermentation tank in a step-by-step manner, with the inoculation amount being 15% of the volume of the pre-fermentation feed solution in the fermentation tank.

[0051] S3. After inoculation of the fermenter, control the fermentation temperature at 52℃, the pressure at 0.02MPa, and the aeration rate at 0.12vvm. Fermentation is carried out at natural pH. When the pH of the fermentation solution drops to 5.1±0.1, add a 30% calcium hydroxide solution to maintain fermentation within this pH range and continue fermentation. When the OD of the fermentation solution... 620 When the concentration reaches 14 or higher, the liquid in the fermenter can be used as a starter culture and inoculated into a fermenter of the same or larger volume.

[0052] S4. Ferment until the glucose concentration in the fermentation liquid drops to 0, stop aeration, continue fermentation for 2.5 hours, then fermentation ends. Add 30% calcium hydroxide solution to adjust the pH to 10, perform plate and frame filtration and MVR evaporation to obtain lactic acid fermentation broth, and then perform acid hydrolysis, directional adsorption extraction and molecular distillation to obtain the finished lactic acid.

[0053] The preparation of organically coated calcium carbonate includes the following steps: surface treatment of calcium carbonate with 1% stearic acid by mass, then placing the surface-treated calcium carbonate in a 2% chitosan solution at 60℃, stirring evenly, filtering, drying, and sieving to obtain organically coated calcium carbonate.

[0054] The preparation method of pretreated corn cob residue is as follows:

[0055] A1. After drying and crushing the corn cob residue, pass it through a 60-mesh sieve, then place it in a 2% sodium hydroxide solution at 50℃ and stir for 0.5-1h. Filter the residue and enzymatically hydrolyze it with cellulase solution at 55℃ and pH 5.2 for 10h. The amount of cellulase used is 25 FPU / g of residue. After the enzymatic hydrolysis is completed, the enzymatic hydrolysate is obtained.

[0056] A2. Add organically coated calcium carbonate and sodium dodecyl sulfate to the enzymatic hydrolysate. The amount of organically coated calcium carbonate added is 5% of the mass of the corn cob residue in the enzymatic hydrolysate, and the amount of sodium dodecyl sulfate added is 0.6% of the mass of the enzymatic hydrolysate. After stirring, let stand, filter, dry, and pass through a 20-mesh sieve to obtain pretreated corn cob residue.

[0057] Comparative Example 1

[0058] The only difference between this comparative example and Example 1 is that, in step S1, pretreated corn cob residue was not added, as detailed below:

[0059] S1. corn starch emulsion with a dry matter mass fraction of 28% was prepared, and 0.14 mg / g of corn starch of high-temperature-resistant a-amylase was added for jet liquefaction, the jet temperature was controlled at 110°C, and maintained for 4 min, then the temperature was reduced to 95°C, and maintained at a pH of 5.2 for 30 min to obtain a liquefied sugar solution, then the liquefied sugar solution was subjected to pre-saccharification treatment, the pre-saccharification temperature was 61°C, the pH was 4.3, the amount of saccharifying enzyme added was 0.38 mg / g of total sugar in the liquefied sugar solution, and the saccharification time was 4 h to obtain a pre-saccharification solution, which was sterilized by steam heating at 110°C for 20 min to obtain a pre-fermentation feed solution;

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is only that no organic coated calcium carbonate is added in the preparation of the pretreated corncob residue, and the specific process is as follows:

[0062] The preparation method of the pretreated corncob residue is as follows:

[0063] A1. The corncob residue was dried and crushed through a 40-mesh screen, then placed in a 50°C, 1% mass fraction of sodium hydroxide solution, stirred for 1 h, filtered, and the filter residue was subjected to enzymatic hydrolysis at 50°C and pH 5.0 for 12 h using a cellulase solution, and the amount of cellulase used was 20 FPU / g of filter residue. The enzymatic hydrolysis was completed to obtain an enzymatic hydrolysis solution;

[0064] A2. Sodium dodecyl sulfate was added to the enzymatic hydrolysis solution, and the amount of sodium dodecyl sulfate added was 0.5% of the mass of the enzymatic hydrolysis solution. After stirring, it was allowed to stand, filtered, dried, and sieved through an 8-mesh screen to obtain pretreated corncob residue.

[0065] Comparative Example 3

[0066] The difference between this comparative example and Example 1 is only that no corncob residue is added in the pretreated corncob residue of step S1, but organic coated calcium carbonate is added, and the specific process is as follows:

[0067] S1. corn starch emulsion with a dry matter mass fraction of 28% was prepared, and 0.14 mg / g of corn starch of high-temperature-resistant a-amylase was added for jet liquefaction, the jet temperature was controlled at 110°C, and maintained for 4 min, then the temperature was reduced to 95°C, and maintained at a pH of 5.2 for 30 min to obtain a liquefied sugar solution, then the liquefied sugar solution was subjected to pre-saccharification treatment, the pre-saccharification temperature was 61°C, the pH was 4.3, the amount of saccharifying enzyme added was 0.38 mg / g of total sugar in the liquefied sugar solution, and the saccharification time was 4 h to obtain a pre-saccharification solution, which was sterilized by steam heating at 110°C for 20 min to obtain a pre-fermentation feed solution.

[0068] The main raw materials and strain information used in the above examples and comparative examples are as follows:

[0069] Corn starch, Henan Jindan Lactic Acid Technology Co., Ltd., water content ≤14%;

[0070] Thermostable alpha-amylase: enzyme activity 20000 U / ml;

[0071] Saccharifying enzyme: enzyme activity 50000 U / ml;

[0072] Bacillus coagulans, JDKJ 1.1201-2312, Henan Lactic Acid Engineering Technology Research Center.

[0073] The main equipment and its specifications used in the above examples and comparative examples are shown in Table 1:

[0074] Table 1

[0075] Equipment name Specification model Pulper φ2000x6000 Injector Q=80m 3 ]]> Lag unit φ500x4000 Lag unit φ1600x2400 Flash tank φ1600x2400 Plate and frame filter press 100 m 2 ]] Buffer tank for liquefied liquid φ2000x4000 Strain tank 60m 3 ]]> Fermentation tank 18m 3 ]]> Fermentation tank 90m 3 ]] Plate filter press 200m 2 ]] Evaporator 20m 3 / h]] Tubular reactor DN200 / DN80 Decomposition reactor 60t Belt filter 40m2 Plate and frame filter press 100 m 2 ]]> Decolorization column φ2200 Ion exchange column φ2200 Neutralization reactor 100 m 3 ]] Decolorization tank 100 m 3 ]] Membrane filtration system Stainless steel ultrafiltration membrane 300 μm

[0076] Effectiveness

[0077] The acid fermentation processes of Examples 1-3 and Comparative Examples 1-3 were scaled up to a single-tank 90 cubic meter fermentation device, the L-lactic acid yield of the lactic acid fermentation liquor was detected, and the time used in the whole fermentation cycle was counted, and the specific results are shown in Table 2:

[0078] Table 2

[0079] L-lactic acid yield (g / L) Fermentation period (h) Example 1 172.3 46 Example 2 171.1 47 Example 3 171.6 47 Comparative Example 1 129.6 63 Comparative Example 2 148.4 52 Comparative Example 3 140.9 50

[0080] From Examples 1-3 and Comparative Examples 1-3, and in combination with the data in Table 1, it can be seen that the method for stably producing L-lactic acid provided by the present application (Examples 1-3) has an L-lactic acid yield of the lactic acid fermentation liquor of 171.1 g / L or more, and a fermentation cycle of 47 h or less, which has a high acid yield and a short fermentation cycle.

[0081] Obviously, the above examples are merely examples for clear illustration, and are not a limitation on the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the patent application claims.

Claims

1. A method for stable production of L-lactic acid by acid fermentation, characterized by, It comprises the following steps: S1. The corn starch is liquefied and pre-saccharified, and the pretreated corncob residue is added to the pre-saccharification solution, which is sterilized after being stirred uniformly to obtain a pre-fermentation feed liquid; S2. Bacillus coagulans is used as the fermentation strain, which is inoculated into the fermentation tank in a step-by-step manner; S3. After inoculation in the fermentation tank, fermentation is carried out, and when the pH of the fermentation feed liquid is reduced to 5.1±0.1, a neutralizing agent is added to maintain the pH of the fermentation feed liquid at 5.1±0.1, and the fermentation is continued; S4. The fermentation is continued for 1.5-2.5h until the glucose concentration in the feed liquid is reduced to 0, and the fermentation is stopped. Plate and frame filtration and MVR evaporation are carried out to obtain a lactic acid fermentation liquid.

2. The method for stable production of L-lactic acid by acid fermentation according to claim 1, characterized by, The pretreated corncob residue is prepared by treating corn cob residue with amylase and then doping with organic coated calcium carbonate.

3. The method for stable production of L-lactic acid by acid fermentation according to claim 2, characterized by, The coating material of the organic coated calcium carbonate is chitosan.

4. The method for stable production of L-lactic acid by acid fermentation according to claim 2, characterized by, The preparation of the organic coated calcium carbonate comprises the following steps: surface treatment of calcium carbonate with stearic acid, soaking the surface-treated calcium carbonate in a chitosan solution with a mass fraction of 1-2% at 50-60℃, filtering, drying, and sieving to obtain the organic coated calcium carbonate.

5. The method for stable production of L-lactic acid by acid fermentation according to claim 1, characterized by, The preparation method of the pretreated corncob residue is as follows: A1. The corncob residue is dried and crushed, heated and stirred in an alkali solution, filtered, and the filter residue is subjected to enzymatic hydrolysis with a cellulase solution to obtain an enzymatic hydrolysis liquid; A2. Organic coated calcium carbonate and sodium dodecyl sulfate are added to the enzymatic hydrolysis liquid, stirred and allowed to stand, filtered, dried, and sieved to obtain the pretreated corncob residue.

6. The method for stable production of L-lactic acid by acid fermentation according to claim 5, characterized by, The amount of organic coated calcium carbonate added is 3-5% of the mass of the corncob residue in the enzymatic hydrolysis liquid.

7. The method for stable production of L-lactic acid by acid fermentation according to claim 5, characterized by, The alkali solution is one or a mixture of sodium hydroxide solution and potassium hydroxide solution, and the mass fraction of the alkali solution is 1-2%.

8. The method for stable production of L-lactic acid by acid fermentation according to claim 1, characterized by, During the liquefaction process, the corn starch is adjusted to corn starch milk, and amylase is added for jet liquefaction. The jet temperature is 108-110℃, and the holding time is 4-5min. Then the pH is adjusted to 5.0-5.3, and the solution is allowed to stand for 20-50min to obtain a liquefied sugar solution.

9. The method for stable production of L-lactic acid by acid fermentation according to claim 1, characterized by, During the pre-saccharification process, the temperature is 60-62℃, the pH is 4.2-4.5, and the amount of saccharifying enzyme added is 0.35-0.40mg / g of the total sugar mass in the liquefied sugar solution, and the saccharification time is 3-5h.

10. The method for stable production of L-lactic acid by acid fermentation according to claim 1, characterized by, The neutralizing agent is a 20-30% (w / w) calcium hydroxide solution. When the fermentation broth OD... 620 When the concentration reaches 14 or higher, the fermentation liquid in the fermenter can be used as a starter culture for inoculation into other fermenters.