Method for separating and extracting sialic acid from fermentation liquor

Abstract

The invention relates to the technical field of bioengineering, in particular to a method for separating and extracting sialic acid from fermentation liquor, which comprises the following steps: filtering and purifying by using an inorganic membrane separation system and an organic ultrafiltration membrane, concentrating by using a reverse osmosis membrane, removing impurities by ion exchange, decoloring, concentrating under reduced pressure and freeze-drying. And finally, a high-purity sialic acid product is obtained at a relatively high yield. The method provided by the invention is simple to operate, a sialic acid finished product with the purity of 99% or above can be obtained after crystallization, and the whole process is green and environment-friendly and has no environmental pollution.

Description

Technical Field

[0001] The invention relates to the technical field of bioengineering, and in particular to a method for separating and extracting sialic acid from fermentation broth. Background Art

[0002] Sialic acid (N-Acetylneuraminic acid, N-acetylneuraminic acid), its molecular formula is C 11 H 19 NO 9 . Sialic acid is an important component of glycoproteins, oligosaccharides and glycolipids. It is widely present in various tissues and organs of humans, vertebrates, and higher invertebrates. It has anti-inflammatory, antiviral, and anti-tumor biological activities, and has important physiological functions such as cell information transmission and immune regulation. At the same time, it can act on the nervous system and play a vital role in the development of the brain and nervous system of mammals. At present, the sources of sialic acid are mainly through natural product extraction, chemical synthesis, and microbial fermentation. The sialic acid content of natural products is low, the extraction process is complicated and the yield is low, which is not suitable for industrial production; the chemical synthesis method requires high temperature, high pressure and other conditions, and the indium used in the chemical synthesis process is toxic, and the subsequent product separation and purification process is complicated, which cannot meet the needs of large-scale production; the microbial synthesis method has the advantages of high yield, mild reaction conditions, and low energy consumption, and has gradually become the most competitive method for sialic acid production. However, due to the production of by-products such as proteins and amino acids in the process of microbial fermentation, an effective and convenient method for separating and extracting sialic acid is needed.

[0003] CN116496330A discloses a method for separating and extracting sialic acid from a fermentation broth, specifically comprising: first, removing the bacterial cells from the sialic acid fermentation broth through a ceramic membrane, then adding magnesium sulfate to obtain a precipitate after centrifugation, adding sodium hydroxide solution to dissolve it, then using a cation exchange resin for adsorption, eluting with clean water to obtain sialic acid, concentrating it, then using acetic acid for crystallization, and then using ethanol and / or isopropanol for decolorization to obtain a sialic acid product. Although this method has a high sialic acid yield and purity, more organic solvents are used in the intermediate crystallization and decolorization, which is not conducive to subsequent recovery.

[0004] CN113956304A discloses a method for separating and extracting sialic acid from fermentation broth, specifically including: first, removing the thalline from the sialic acid fermentation broth through a ceramic membrane, obtaining a clear night, and heating the obtained clear liquid to 75 ° C by a plate heat exchanger, removing foreign proteins by centrifugation, decolorizing by a decolorizing resin, using a strong base anion resin for ion exchange, eluting with a NaCl solution, and then desalting with a 500Da nanofiltration membrane, concentrating, spray drying, and microwave drying to obtain pure sialic acid. The sialic acid purity finally obtained by the method is more than 98%, the yield is more than 90%, and the whiteness is more than 90, but its operating steps are relatively complicated, requiring the use of resins twice, desalting, and finally obtaining pure sialic acid through two dryings. This method has cumbersome steps, is time-consuming and labor-intensive, and is not conducive to large-scale industrial production.

[0005] Therefore, the present invention aims to provide a method for extracting sialic acid which has simple and easy process, low separation cost, higher purity of the obtained finished product and is suitable for large-scale industrial production. Summary of the invention

[0006] The present invention provides a method for separating and extracting sialic acid from a fermentation broth, which is used to solve the problems in the prior art that a large amount of organic solvent is used, which is not conducive to subsequent recovery; or the purification steps are complicated, time-consuming and labor-intensive, which is not conducive to large-scale industrial production.

[0007] Specifically, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a method for separating and extracting sialic acid from a fermentation broth, wherein the fermentation broth is purified using an inorganic membrane separation system and an ultrafiltration membrane in sequence, then concentrated using a reverse osmosis membrane, then adsorbed and eluted using an ion exchange resin, and finally decolorized using a decolorizing resin, concentrated under reduced pressure, and freeze-dried to obtain sialic acid with a purity of more than 99%; wherein the pore size of the inorganic membrane of the inorganic membrane separation system is 30-200nm; the molecular weight cutoff of the ultrafiltration membrane is 1000-5000Da; and the pore size of the reverse osmosis membrane is 0.1-10nm.

[0008] Preferably, the operating temperature of the inorganic membrane separation system is 25-60°C, and the operating pressure is 0.05-0.2 MPa.

[0009] Preferably, during the process of collecting the filtrate using the inorganic membrane separation system, collection is stopped when the solid content in the fermentation broth is lower than 1.0 g / L.

[0010] Preferably, the operating temperature of ultrafiltration membrane purification is 25-45°C and the operating pressure is 0.05-0.2 MPa.

[0011] Preferably, in the process of collecting the filtrate using the ultrafiltration membrane, the collection is stopped when the solid content in the inorganic membrane filtrate is lower than 0.5 g / L.

[0012] Preferably, the operating temperature of the reverse osmosis membrane concentration is 25-45°C, and the operating pressure is 0.05-0.2 MPa.

[0013] Preferably, the ion exchange resin is a strong base anion exchange resin.

[0014] More preferably, the strong base anion resin is a gel-type ion exchange resin or a macroporous ion exchange resin.

[0015] Further preferably, the model of the strong base anion exchange resin is D202 or D260 or D201.

[0016] Preferably, the present invention pumps the filtrate concentrated by the reverse osmosis membrane into the ion exchange resin for adsorption, the injection flow rate is 0.5-2BV / h, and after adsorption saturation, 8%±1% formic acid solution is used for elution, the elution flow rate is 0.5-2BV / h, and the sialic acid eluate with a purity of more than 70% is collected.

[0017] Preferably, the decolorizing resin of the present invention adopts a cationic decolorizing resin, the injection flow rate is 1-2BV / h, and after adsorption saturation, it is eluted with pure water, the elution flow rate is 3-5BV / h, and the eluate is collected. When the conductivity is <1000μs / cm, the collection of the decolorized liquid is stopped to obtain a decolorized liquid.

[0018] Preferably, in the present invention, the collected decolorized liquid is concentrated under reduced pressure to a solid content of 60-70%, and then freeze-dried.

[0019] In a second aspect, the present invention also provides the use of the above-mentioned method for separating and extracting sialic acid from fermentation broth in the industrial production of sialic acid.

[0020] Beneficial effects: The present invention provides a method for separating and extracting sialic acid from a fermentation broth, wherein the fermentation broth is purified by an inorganic membrane separation system and an ultrafiltration membrane in sequence, then concentrated by a reverse osmosis membrane, then adsorbed and eluted by an ion exchange resin, and finally decolorized by a decolorizing resin, concentrated under reduced pressure, and freeze-dried in sequence, and finally a high-purity sialic acid product is obtained with a high yield. The method provided by the present invention is simple to operate, and a sialic acid product with a purity of more than 99% can be obtained after crystallization, and the whole process is green and environmentally friendly, without environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be described below.

[0022] Figure 1 This is a process flow chart for extracting sialic acid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention provides a method for separating and extracting sialic acid from a fermentation broth, the method comprising the following steps: using an inorganic membrane separation system to remove bacteria, part of proteins and pigments in the fermentation broth, and collecting a filtrate; using an ultrafiltration membrane to further remove impurities such as proteins and pigments in the fermentation broth from the filtrate; using a reverse osmosis membrane to concentrate the filtrate of the ultrafiltration membrane; then using an ion exchange resin to adsorb sialic acid, and obtaining a sialic acid eluate after elution; and sequentially decolorizing the sialic acid eluate with a decolorizing resin, concentrating under reduced pressure, and freeze-drying to obtain sialic acid with a purity of more than 99%.

[0024] In some embodiments of the present invention, the inorganic membrane pore size of the inorganic membrane separation system is 30-200 nm, the operating temperature is 25-60° C., and the operating pressure is 0.05-0.2 MPa. During the collection of the inorganic membrane filtrate, the collection is stopped when the content of solids (mixed components including sialic acid) in the fermentation broth is less than 1.0 g / L.

[0025] In some embodiments of the present invention, the ultrafiltration membrane has a molecular weight cutoff of 1000-5000Da, an operating temperature of 25-45°C, an operating pressure of 0.05-0.2MPa, and during the filtrate collection process, collection is stopped when the solid content in the inorganic membrane filtrate is lower than 0.5g / L.

[0026] In some embodiments of the present invention, a reverse osmosis membrane is used for concentration, the system pore size of the reverse osmosis membrane is 0.1-10 nm, the operating temperature is 25-45° C., and the operating pressure is 0.05-0.2 MPa.

[0027] The present invention firstly concentrates the filtrate by reverse osmosis membrane before using ion exchange resin to adsorb sialic acid. This step is effective and necessary. If it is not concentrated, directly removing impurities by ion exchange resin will reduce the adsorption amount of sialic acid, affect the adsorption effect, reduce the yield, and also increase the ion exchange time.

[0028] Furthermore, the present invention uses a decolorizing resin to decolorize the eluate obtained by ion exchange. In the existing method for decolorizing sialic acid, activated carbon decolorization is generally used. The temperature during decolorization is high, and the high temperature will cause the sialic acid solution to change color, affecting the subsequent purification step. The higher the decolorization temperature, the greater the energy loss. The use of decolorizing resin can reduce the use of activated carbon, and it can be carried out at room temperature to reduce energy consumption.

[0029] In some embodiments of the present invention, the ion exchange resin is a strongly basic anion exchange resin, and the strongly basic anion exchange resin is a gel-type ion exchange resin or a macroporous ion exchange resin. Further preferably, the model of the strongly basic anion exchange resin is D202, D260 or D201.

[0030] Furthermore, the present invention decolorizes the eluate obtained by ion exchange by using a decolorizing resin, concentrates under reduced pressure, and freeze-dries. The formic acid in the concentrate can be removed by reduced pressure concentration and freeze-drying. At the same time, freeze-drying will not denature sialic acid and cause the color to deepen, thereby further improving the purity of sialic acid.

[0031] In some embodiments of the present invention, sialic acid is adsorbed by ion exchange resin, and the step of obtaining sialic acid eluate after elution comprises: pumping the sialic acid filtrate concentrated by reverse osmosis membrane into ion exchange resin for adsorption, the injection flow rate is 0.5-2BV / h, after adsorption saturation, eluting with 8% (w / w) formic acid solution, the elution flow rate is 0.5-2BV / h, and collecting sialic acid eluate with a purity of more than 70%.

[0032] In some embodiments of the present invention, the step of decolorizing with a decolorizing resin includes: the decolorizing resin uses a cationic decolorizing resin, the injection flow rate is 1-2BV / h, after adsorption saturation, it is eluted with pure water, the elution flow rate is 3-5BV / h, the eluate is collected, and the collection of the decolorized solution is stopped when the conductivity is <1000μs / cm to obtain a sialic acid decolorized solution.

[0033] In some embodiments of the present invention, the collected decolorized liquid is concentrated under reduced pressure to a solid content of 60-70% (m / v), and then the collected concentrated liquid is dried using a freeze dryer.

[0034] In a more specific optional embodiment provided by the present invention, the method for separating and extracting sialic acid from the fermentation broth specifically comprises the following steps: a. Pump the fermentation liquid rich in sialic acid into the inorganic membrane separation system, collect the inorganic membrane filtrate, and stop collecting when the solid content in the fermentation liquid is lower than 1.0 g / L; the pore size of the inorganic membrane separation system is 30-200 nm.

[0035] b. The filtrate obtained in step a is further treated with an ultrafiltration membrane to remove impurities such as protein and pigment in the inorganic membrane filtrate. The ultrafiltration membrane has a molecular weight cutoff of 1000-5000Da, an operating temperature of 25-45°C, and an operating pressure of 0.05-0.2MPa. When the solid content in the inorganic membrane filtrate is less than 0.5g / L, collection is stopped to obtain an ultrafiltration membrane filtrate.

[0036] c. The ultrafiltration membrane filtrate obtained in step b is concentrated using a reverse osmosis membrane. The reverse osmosis membrane has a pore size of 0.1-10 nm, preferably 0.5-2 nm, an operating temperature of 25-45° C., and an operating pressure of 0.05-0.2 MPa.

[0037] d. The concentrated solution obtained in step c is pumped into an ion exchange column, adsorbed by a strong base anion exchange resin at an injection flow rate of 0.5-2 BV / h, and eluted with 8% (w / w) formic acid solution after adsorption saturation at an elution flow rate of 0.5-2 BV / h, and a high-purity sialic acid eluate with a purity of more than 70% is collected.

[0038] e. Decolorize the high-purity eluate obtained in step d using a decolorizing resin at an injection flow rate of 1-2 BV / h. After adsorption saturation, elute with pure water at an elution flow rate of 3-5 BV / h. Collect the eluate until the conductivity is less than 1000 μs / cm, then stop collecting the decolorized solution to obtain a sialic acid decolorized solution.

[0039] f. Concentrate the decolorized solution obtained in step e under reduced pressure until the solid content is 60-70% (m / v), and freeze-dry the concentrated solution to obtain pure sialic acid.

[0040] Wherein, the sialic acid-rich fermentation broth is prepared by a sialic acid-producing strain through a microbial fermentation method. The content of sialic acid in the sialic acid-rich fermentation broth is preferably above 60 g / L. Extracting sialic acid from the sialic acid-rich fermentation broth has low raw material cost, simple operation, high product purity, reduced energy consumption, and is easy for industrial production compared to methods such as natural product extraction and chemical synthesis.

[0041] In this article, the endpoints and any values ​​of the disclosed ranges are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "specific implementation methods", or "some specific implementation methods" 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 embodiment 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 may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0043] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are 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.

[0044] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased through regular channels.

[0045] Example 1

[0046] This embodiment provides a method for separating and extracting sialic acid from a fermentation broth. The process flow chart is as follows: Figure 1 As shown, the specific steps are as follows: a. Add 10 L of sialic acid fermentation broth with a sialic acid content of 65.0 g / L into an inorganic membrane separation system, wherein the pore size of the inorganic membrane of the inorganic membrane separation system is 30 nm, the operating temperature is 30° C., and the operating pressure is 0.2 MPa; when the solid content in the fermentation broth is lower than 1.0 g / L, stop collecting to obtain an inorganic membrane filtrate.

[0047] b. Using an ultrafiltration membrane to treat the inorganic membrane filtrate obtained in step a to further remove impurities such as protein and pigment in the inorganic membrane filtrate. The ultrafiltration membrane has a molecular weight cutoff of 2000Da, an operating temperature of 35°C, and an operating pressure of 0.1MPa; when the solid content in the inorganic membrane filtrate is lower than 0.5g / L, the collection is stopped to obtain an ultrafiltration membrane filtrate.

[0048] c. Using a reverse osmosis membrane to treat the ultrafiltration membrane filtrate obtained in step b to obtain a concentrated solution; the pore size of the reverse osmosis membrane is 0.5 nm; the operating temperature is 40° C., and the operating pressure is 0.1 MPa.

[0049] d. The concentrated solution obtained in step c is pumped into an ion exchange column, adsorbed by a strong base anion exchange resin (D260) at an injection flow rate of 1 BV / h, and eluted with 8% (w / w) formic acid solution at an elution flow rate of 1 BV / h after adsorption saturation, and the high-purity sialic acid eluate with a purity of more than 70% is collected.

[0050] e. The high-purity eluate obtained in step d was treated with a decolorizing resin for decolorization: the injection flow rate was 1.5 BV, the eluate was eluted with pure water, the elution flow rate was 3 BV, and the decolorized solution was collected to obtain a sialic acid decolorized solution with a transmittance of 97.7%.

[0051] f. The decolorized solution obtained in step e was concentrated under reduced pressure to a solid content of 70% (m / v), and the obtained concentrate was freeze-dried to obtain 587.73 g of pure sialic acid with a yield of 90.42% and a purity of 99.78%.

[0052] Example 2

[0053] This embodiment provides a method for separating and extracting sialic acid from a fermentation broth. The process flow chart is as follows: Figure 1 As shown, the specific steps are as follows: a. Add 10 L of sialic acid fermentation broth with a sialic acid content of 67.0 g / L into an inorganic membrane separation system, wherein the pore size of the inorganic membrane of the inorganic membrane separation system is 100 nm, the operating temperature is 50° C., and the operating pressure is 0.2 MPa; when the solid content in the fermentation broth is lower than 1.0 g / L, stop collecting to obtain an inorganic membrane filtrate.

[0054] b. Using an ultrafiltration membrane to treat the inorganic membrane filtrate obtained in step a to further remove impurities such as protein and pigment in the inorganic membrane filtrate. The ultrafiltration membrane has a molecular weight cutoff of 1000 Da, an operating temperature of 35° C., and an operating pressure of 0.2 MPa; when the solid content in the inorganic membrane filtrate is less than 0.5 g / L, the collection is stopped to obtain an ultrafiltration membrane filtrate.

[0055] c. treating the ultrafiltration membrane filtrate obtained in step b with a reverse osmosis membrane to obtain a concentrated solution; the reverse osmosis membrane has a pore size of 0.5 nm; the operating temperature is 35° C., and the operating pressure is 0.1 MPa; d. The concentrated solution obtained in step c is pumped into an ion exchange column, adsorbed by a strong base anion exchange resin (D260) at an injection flow rate of 1 BV / h, and eluted with 8% (w / w) formic acid solution at an elution flow rate of 1 BV / h after adsorption saturation, and the high-purity sialic acid eluate with a purity of more than 70% is collected.

[0056] e. Treat the high-purity eluate obtained in step d with a decolorizing resin for decolorization: the injection flow rate is 1 BV, the eluate is eluted with pure water, the elution flow rate is 3 BV, and the decolorized solution is collected to obtain a sialic acid decolorized solution with a transmittance of 98.5%.

[0057] f. The decolorized solution obtained in step e was concentrated under reduced pressure to a solid content of 65% (m / v), and the obtained concentrate was freeze-dried to obtain 605.55 g of pure sialic acid with a yield of 87.38% and a purity of 99.25%.

[0058] Example 3

[0059] This embodiment provides a method for separating and extracting sialic acid from a fermentation broth. The process flow chart is as follows: Figure 1 As shown, the specific steps are as follows: a. Take 10L of sialic acid fermentation liquid with a sialic acid content of 70.0g / L and add it into an inorganic membrane separation system. The pore size of the inorganic membrane of the inorganic membrane separation system is 200nm, the operating temperature is 45°C, and the operating pressure is 0.2MPa. When the solid content in the fermentation liquid is lower than 1.0g / L, stop collecting to obtain the inorganic membrane filtrate.

[0060] b. Using an ultrafiltration membrane to treat the inorganic membrane filtrate obtained in step a to further remove impurities such as protein and pigment in the inorganic membrane filtrate. The ultrafiltration membrane has a molecular weight cutoff of 5000Da, an operating temperature of 35°C, and an operating pressure of 0.1MPa; when the solid content in the inorganic membrane filtrate is lower than 0.5g / L, the collection is stopped to obtain an ultrafiltration membrane filtrate.

[0061] c. Using a reverse osmosis membrane to treat the ultrafiltration membrane filtrate obtained in step b to obtain a concentrated solution; the pore size of the reverse osmosis membrane is 0.5 nm; the operating temperature is 37° C., and the operating pressure is 0.1 MPa.

[0062] d. The concentrated solution obtained in step c is pumped into an ion exchange column, adsorbed by a strong base anion exchange resin (D260) at an injection flow rate of 1 BV / h, and eluted with 8% (w / w) formic acid solution at an elution flow rate of 1 BV / h after adsorption saturation, and the high-purity sialic acid eluate with a purity of more than 70% is collected.

[0063] e. The high-purity eluate obtained in step d was treated with a decolorizing resin for decolorization: the injection flow rate was 2 BV, the elution was pure water, the elution flow rate was 5 BV, and the decolorized solution was collected to obtain a sialic acid decolorized solution with a transmittance of 98.3%.

[0064] f. The decolorized solution obtained in step e was concentrated under reduced pressure to a solid content of 68% (m / v), and the concentrated solution was freeze-dried to obtain 597.94 g of pure sialic acid with a yield of 85.42% and a purity of 99.03%.

[0065] Example 4

[0066] This example provides a method for separating and extracting sialic acid from a fermentation broth, which differs from Example 1 in that the strong base anion resin used in step d is D202. The result is that the sialic acid yield is 70.76% and the purity is 99.13%.

[0067] Example 5

[0068] This example provides a method for separating and extracting sialic acid from a fermentation broth, which differs from Example 1 in that the strong base anion resin used in step d is D201. The result is that the yield of sialic acid is 69.17% and the purity is 99.27%.

[0069] Comparative Example 1

[0070] This comparative example provides a method for separating and extracting sialic acid from a fermentation broth, which differs from Example 1 in that the drying method described in step f is vacuum drying at 60°C. The result is that the sialic acid yield is 84.17% and the purity is 98.07%. The color of the dried product is pink, the color of the freeze-dried product is pure white, and the dried product is easy to agglomerate, and the crystal particles are large.

[0071] Comparative Example 2

[0072] This comparative example provides a method for separating and extracting sialic acid from a fermentation broth. The difference between the comparative example and Example 1 is that the decolorization method used in step e is to use activated carbon for decolorization, and a sialic acid decolorization solution is obtained, and the transmittance is 94.2%. As a result, the sialic acid yield is 80.42% and the purity is 96.38%.

[0073] Comparative Example 3

[0074] This comparative example provides a method for separating and extracting sialic acid from a fermentation broth, which differs from Example 1 in that step c is missing (i.e., directly pumping the ultrafiltration membrane filtrate obtained in step b into an ion exchange column). As a result, the sialic acid yield is 67.42% and the purity is 92.38%.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating and extracting sialic acid from a fermentation broth, characterized in that: The fermentation broth is purified by an inorganic membrane separation system and an ultrafiltration membrane in sequence, then concentrated by a reverse osmosis membrane, eluted by adsorption using an ion exchange resin, and finally decolorized by a decolorizing resin, concentrated under reduced pressure, and freeze-dried to obtain sialic acid with a purity of more than 99%; wherein, the pore size of the inorganic membrane of the inorganic membrane separation system is 30-200nm; the molecular weight cutoff of the ultrafiltration membrane is 1000-5000Da; and the pore size of the reverse osmosis membrane is 0.1-10nm.

2. The method for separating and extracting sialic acid from a fermentation broth according to claim 1, characterized in that: The operating temperature of the inorganic membrane separation system is 25-60°C and the operating pressure is 0.05-0.2MPa; Preferably, during the process of collecting the filtrate using the inorganic membrane separation system, collection is stopped when the solid content in the fermentation broth is lower than 1.0 g / L.

3. The method for separating and extracting sialic acid from a fermentation broth according to claim 1 or 2, characterized in that: The operating temperature of ultrafiltration membrane purification is 25-45°C and the operating pressure is 0.05-0.2MPa; Preferably, in the process of collecting the filtrate using the ultrafiltration membrane, the collection is stopped when the solid content in the inorganic membrane filtrate is lower than 0.5 g / L.

4. The method for separating and extracting sialic acid from a fermentation broth according to any one of claims 1 to 3, characterized in that: The operating temperature of reverse osmosis membrane concentration is 25-45°C and the operating pressure is 0.05-0.2MPa.

5. The method for separating and extracting sialic acid from a fermentation broth according to any one of claims 1 to 4, characterized in that: The ion exchange resin is a strong base anion exchange resin; Preferably, the strong base anion resin is a gel-type ion exchange resin or a macroporous ion exchange resin.

6. The method for separating and extracting sialic acid from a fermentation broth according to claim 5, characterized in that: The model of the strong base anion exchange resin is D202, D260 or D201.

7. The method for separating and extracting sialic acid from a fermentation broth according to any one of claims 1 to 6, characterized in that: The filtrate concentrated by reverse osmosis membrane is pumped into ion exchange resin for adsorption, and the injection flow rate is 0.5-2BV / h. After adsorption saturation, 8%±1% formic acid solution is used for elution, and the elution flow rate is 0.5-2BV / h. The sialic acid eluate with a purity of more than 70% is collected.

8. The method for separating and extracting sialic acid from a fermentation broth according to any one of claims 1 to 7, characterized in that: The decolorizing resin uses a cationic decolorizing resin with an injection flow rate of 1-2BV / h. After adsorption saturation, it is eluted with pure water at an elution flow rate of 3-5BV / h. The eluate is collected until the conductivity is less than 1000μs / cm, and the collection of the decolorized solution is stopped to obtain a decolorized solution.

9. The method for separating and extracting sialic acid from a fermentation broth according to claim 8, characterized in that: The collected decolorized liquid is concentrated under reduced pressure to a solid content of 60-70%, and then freeze-dried.

10. Use of the method according to any one of claims 1 to 9 in the industrial production of sialic acid.

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