Method for producing lactic acid based on acidic buffer agent

Abstract

The invention discloses a method for producing lactic acid based on an acidic buffer agent, and belongs to the field of lactic acid production. The invention discloses a method for producing lactic acid based on an acidic buffering agent. The method comprises the following steps: inoculating lactic acid bacteria into fermentation liquor added with the acidic buffering agent; the fermentation liquor inoculated with the lactic acid bacteria is placed in a fermentation tank to be subjected to sterile culture, and the PH value is monitored; when the pH value is reduced to 3.8, adding ammonia water, adjusting the pH value to 5, and maintaining the pH value until the fermentation is finished; and after fermentation is finished, centrifuging and filtering to remove cells in the fermentation liquid, and extracting lactic acid. The strain is stressed to adapt to the existing pH value under the environment of the acidic buffer agent, so that the strain can still continuously grow and metabolize to produce new lactic acid when the pH value is 5; besides, ammonia water is added in the fermentation process, so that the strain can supplement an inorganic nitrogen source and adjust the pH value, a large amount of solid waste is not generated in the lactic acid production process, and the separation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of lactic acid production, and particularly relates to a method for producing lactic acid based on an acidic buffer. Background Art

[0002] The existing lactic acid production is mainly produced by fermentation. In this process, a large amount of lactic acid will be produced to reduce the pH value in the fermentation tank. The lactic acid bacteria commonly used in lactic acid fermentation usually have an optimum pH value between 6.5 and 7.5. When the pH reaches below 3.8, the activity of the enzyme will be inhibited, causing the metabolism to stagnate. In order to avoid a significant impact on the fermentation metabolism of the strain, the prior art uses a calcium salt method to add a large amount of neutralizer (calcium hydroxide) to neutralize the pH value. However, the calcium salt method will produce a large amount of solid waste, increasing the subsequent separation cost. Therefore, a method for producing lactic acid based on an acidic buffer is proposed. Summary of the invention

[0003] In view of the deficiencies of the prior art, the object of the present invention is to provide a method for producing lactic acid based on an acidic buffer, which solves the problems in the prior art.

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

[0005] A method for producing lactic acid based on an acidic buffer comprises the following steps:

[0006] S1, inoculating lactic acid bacteria into a fermentation broth to which an acidic buffer is added;

[0007] S2, placing the fermentation liquid inoculated with lactic acid bacteria in a fermentation tank for sterile culture, and monitoring the pH value;

[0008] S3, when the pH drops to 3.8, add ammonia water to adjust the pH value until the fermentation is completed.

[0009] S4, after the fermentation is completed, the cells in the fermentation liquid are removed by centrifugation and filtration, and then lactic acid is extracted.

[0010] Furthermore, in S1, the initial pH value of the fermentation liquid is 5.

[0011] Furthermore, the concentration of the acidic buffer is 2 g / L.

[0012] Further, in S1, the fermentation broth includes: 50 g / L glucose, 5 g / L amino acid, 1 g / L ammonium chloride, 2 g / L sodium chloride, 2 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate, 0.1 g / L calcium sulfate, 0.05 g / L ferrous sulfate, 0.01 g / L manganese sulfate, 0.01 g / L zinc sulfate, 0.01 g / L thiamine, and 2 g / L acidic buffer.

[0013] Furthermore, it is characterized in that the acidic buffer is L-lactic acid or DL-lactic acid.

[0014] Furthermore, the lactic acid bacteria are: Lactobacillus sp, Lactobacillus acidophilus, Lactobacillus plantarum or Lactobacillus rhamnosus.

[0015] Further, in S2, the temperature of the sterile culture was 32°C and the ventilation rate was 1 vvm.

[0016] Further, in S3, the pH value is adjusted to 5 and maintained until the end of fermentation.

[0017] Beneficial effects of the present invention:

[0018] 1. By adding lactic acid as a buffer in the early nutrient solution, the pH is adjusted to 5, so that the strain is forced to adapt to the existing pH value in an environment where lactic acid already exists. At this time, the added lactic acid plays a buffering role, and the strain can continue to grow and metabolize to produce new lactic acid at a pH of 5.

[0019] 2. When the strain grows to a certain stage, the pH reaches 3.8 due to the accumulation of a large amount of lactic acid, and the strain is inhibited. At this time, the present invention adds a certain amount of ammonia water in the fermentation tank. After the ammonia water dissolves in the fermentation liquid, the pH value will be increased to 5. At this time, the strain can both supplement the inorganic nitrogen source and adjust the pH. In addition, a large amount of solid waste will not be generated in the process of producing lactic acid, thereby reducing the separation cost. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example

[0022] A method for producing lactic acid based on an acidic buffer comprises the following steps:

[0023] S1, inoculating Lactobacillus sp. into a fermentation broth, adding L-lactic acid as a buffer to the fermentation broth, the concentration of L-lactic acid is 2 g / L, and adjusting the pH to 5;

[0024] The fermentation broth includes: 50 g / L glucose, 5 g / L amino acids, 1 g / L ammonium chloride, 2 g / L sodium chloride, 2 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate, 0.1 g / L calcium sulfate, 0.05 g / L ferrous sulfate, 0.01 g / L manganese sulfate, 0.01 g / L zinc sulfate, 0.01 g / L thiamine, 2 g / L L-lactic acid, and then water is added to 1 L;

[0025] S2, the fermentation liquid inoculated with lactobacillus is placed in a fermentation tank for sterile culture, and the pH value is monitored; the temperature is controlled at 32°C, and the ventilation rate is controlled at 1vvm. At this stage, the lactobacillus is in the proliferation stage, and consumes the sugar in the fermentation liquid through fermentation to produce lactic acid;

[0026] S3, when the pH drops to 3.8, add ammonia water, maintain the pH value at 5, and ferment for 48 hours until the fermentation is completed.

[0027] S4, after the fermentation is completed, the cells in the fermentation liquid are removed by centrifugation and filtration, and then lactic acid is extracted.

[0028] Of course, the lactic acid bacteria include but are not limited to Lactobacillus sp. In other embodiments, the lactic acid bacteria may also be selected from: Lactobacillus acidophilus, Lactobacillus plantarum or Lactobacillus rhamnosus.

[0029] And in other embodiments, the buffer can also be DL-lactic acid.

[0030] Comparative Example

[0031] This comparative example introduces a method for producing lactic acid based on a calcium salt method, which specifically comprises the following steps:

[0032] Step 1, inoculating the same amount of Lactobacillus sp. as in the example into the fermentation broth, and adjusting the pH to 6.5;

[0033] The fermentation broth includes: 50 g / L glucose, 5 g / L amino acids, 1 g / L ammonium chloride, 2 g / L sodium chloride, 2 g / L potassium dihydrogen phosphate, 0.5 g / L magnesium sulfate, 0.1 g / L calcium sulfate, 0.05 g / L ferrous sulfate, 0.01 g / L manganese sulfate, 0.01 g / L zinc sulfate, 0.01 g / L thiamine; then add water to 1 L;

[0034] Step 2: Place the fermentation liquid inoculated with lactobacillus in a fermentation tank for sterile culture and monitor the pH value; the temperature is controlled at 32°C and the ventilation rate is controlled at 1vvm. At this stage, the lactobacillus is in the proliferation stage and consumes the sugar in the fermentation liquid through fermentation to produce lactic acid;

[0035] Step 3, when the pH drops to 3.8, add calcium hydroxide to maintain the pH at 5, and ferment for 48 hours until the fermentation is completed.

[0036] Step 4: After the fermentation is completed, the cells and solid waste in the fermentation liquid are removed by centrifugation, filtration and separation to extract lactic acid.

[0037] Experimental testing

[0038] After the fermentation was completed, the lactic acid and glucose concentrations in the fermentation broth of the embodiment and the comparative example were measured by high performance liquid chromatography (HPLC) (sugar consumption was calculated); the results are shown in Table 1 below:

[0039] Table 1 Fermentation parameters and test results of examples and comparative examples

[0040]

[0041] As can be seen from Table 1, after fermentation in the embodiment, the concentration of lactic acid produced is 75g / L, and the actual lactic acid content is 75g / L×1.5L=112.5g; while the concentration of lactic acid in the comparative example is 66g / L, and the actual lactic acid output is 66g / L×1.36L=89.76g; even if the lactic acid added at the beginning is deducted in the embodiment (2g / L×1L=2g), the actual lactic acid output in the embodiment is 110.5g, which is significantly higher than the lactic acid output in the comparative example; this is because lactic acid is used as a buffer in the embodiment, and the strain can better adapt to the acidic environment during the fermentation process, thereby increasing the output.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0043] 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 to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for producing lactic acid based on an acidic buffer, characterized in that: The following steps are involved: S1, inoculating lactic acid bacteria into a fermentation broth to which an acidic buffer is added; S2, placing the fermentation liquid inoculated with lactic acid bacteria in a fermentation tank for sterile culture, and monitoring the pH value; S3, when the pH drops to 3.8, add ammonia water to adjust the pH value until the fermentation is completed. S4, after the fermentation is completed, the cells in the fermentation liquid are removed by centrifugation and filtration, and then lactic acid is extracted.

2. A method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: In S1, the initial pH value of the fermentation broth was 5.

3. The method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: The concentration of the acidic buffer is 2 g / L.

4. The method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: In S1, the fermentation broth includes: 50g / L glucose, 5g / L amino acid, 1g / L ammonium chloride, 2g / L sodium chloride, 2g / L potassium dihydrogen phosphate, 0.5g / L magnesium sulfate, 0.1g / L calcium sulfate, 0.05g / L ferrous sulfate, 0.01g / L manganese sulfate, 0.01g / L zinc sulfate, 0.01g / L thiamine, and 2g / L acidic buffer.

5. A method for producing lactic acid based on an acidic buffer according to claim 1, 3, 4 or 5, characterized in that: The acidic buffer is L-lactic acid or DL-lactic acid.

6. The method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: The lactic acid bacteria are: Lactobacillus sp, Lactobacillus acidophilus, Lactobacillus plantarum or Lactobacillus rhamnosus.

7. The method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: In S2, the temperature of the sterile culture was 32°C and the aeration rate was 1 vvm.

8. The method for producing lactic acid based on an acidic buffer according to claim 1, characterized in that: In S3, the pH value is adjusted to 5 and maintained until the end of fermentation.

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