CN109776626B - Method for preventing sialic acid aqueous solution from discoloring - Google Patents
Method for preventing sialic acid aqueous solution from discoloring Download PDFInfo
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Abstract
The invention provides a method for preventing discoloration of an aqueous sialic acid solution. The method comprises the following steps: adjusting the pH of the sialic acid aqueous solution to 5.0-12.0. After the method is used, the processed sialic acid aqueous solution is placed in a low-temperature environment, a normal-temperature environment or a high-temperature environment, the sialic acid aqueous solution is always kept as a colorless solution and is very stable, and the sialic acid aqueous solution is kept for at least two years in the normal-temperature environment.
Description
Technical Field
The invention relates to the field of industrial production, in particular to a method for preventing sialic acid aqueous solution from discoloring.
Background
Sialic acid has the functions of improving intelligence and memory, resisting bacteria and killing viruses and the like, and is widely applied to medicines, foods and cosmetics. In these applications, sialic acid samples are often used in the form of aqueous solutions, which requires that the aqueous sialic acid samples must be stable, not only in terms of content, but also in other aspects, such as appearance, colour, etc. The sialic acid aqueous solution is colorless and transparent, but the sialic acid aqueous solution is unstable, and the color of the aqueous solution gradually changes from colorless to light yellow along with the prolonging of time if the storage condition is not proper, and then gradually deepens, so that the application of the sialic acid is seriously influenced.
Disclosure of Invention
In view of the above problems, a first object of the present invention is to provide a method for preventing discoloration of an aqueous sialic acid solution, the method comprising the steps of:
adjusting the pH of the sialic acid aqueous solution to 5.0-12.0.
After the method is used, the processed sialic acid aqueous solution is placed in a low-temperature environment, a normal-temperature environment or a high-temperature environment, the sialic acid aqueous solution is always kept as a colorless solution and is very stable, and the sialic acid aqueous solution is kept for at least two years in the normal-temperature environment.
In a preferred embodiment of the present invention, the pH of the aqueous sialic acid solution is adjusted to 6.0 to 8.0.
In a preferred embodiment of the invention, the aqueous sialic acid solution is prepared by dissolving sialic acid in water; the purity of the sialic acid is 80-99%.
In the present invention, the sialic acid is preferably sialic acid obtained by the extraction method disclosed in CN 201811372637.8. All solutions disclosed in CN201811372637.8 are included in the present invention.
The sialic acid is preferably extracted by a sialic acid solution obtained by pretreating a sialic acid monomer source, and the sialic acid solution is obtained by adjusting the pH, concentrating, purifying, heating, concentrating, acidifying and crystallizing; the sialic acid monomer source is polysialic acid or cubilose.
The sialic acid monomer is preferably polysialic acid, and the pretreatment is hydrolysis. The hydrolysis reaction of the polysialic acid further comprises: adding an acid substance into the polysialic acid until the pH of the solution is 1-2, and reacting for 2-4 hours at the temperature of 80-90 ℃. Wherein, 10-30g/L polysialic acid fermentation liquor is filtered by adopting a 50-300nm ceramic membrane, and then filtered by adopting an ultrafiltration membrane with the specification of 8-12KDa until the solid content of the solution is less than 3 times of the content of the polysialic acid, so as to obtain the polysialic acid solution. Among them, the pH adjustment is particularly preferably: sodium hydroxide is added to the solution to a pH of 5-7 and a sialic acid salt solution is obtained. The concentration and purification specifically comprises the following steps: ultrafiltration treatment and nanofiltration treatment. The ultrafiltration treatment comprises: filtering the decolorized solution with 0.5-2KDa ultrafiltration membrane to remove unhydrolyzed polysialic acid. The nanofiltration treatment comprises the following steps: desalting the sialic acid salt solution by using a 200-400Da nanofiltration membrane to ensure that the solid content of the sialic acid salt solution is less than 3 times of the sialic acid content. The concentration by heating preferably comprises: the nanofiltration solution was concentrated 8-12 times under vacuum with heating to achieve a concentration of about 200-500g/L sodium sialylate in the concentrated solution. Acidifying crystallization and drying include: adding acidic substance into the concentrated solution after heating and concentrating until the pH of the solution is 1-2, crystallizing at 0-10 deg.C for 5-10 hr to obtain crystal, filtering the crystal, washing, and vacuum drying to obtain sialic acid.
In a preferred embodiment of the invention, the concentration of the aqueous sialic acid solution is between 1% and 20%, preferably between 2% and 5%. In a preferred embodiment of the present invention, the aqueous sialic acid solution is adjusted to a pH of 5.0 to 12.0 using an alkaline solution. Wherein the alkaline solution is sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.
According to the invention, the pH value of the sialic acid aqueous solution is 5.0-12.0, the sialic acid aqueous solution can not change color after being placed in a low-temperature or normal-temperature environment for at least 2 years, and meanwhile, the sialic acid aqueous solution can not change color after being hermetically placed in an environment at 80 ℃ for at least 6 months, and can not change color after being hermetically placed in an environment at 60 ℃ for at least 12 months.
Drawings
FIG. 1 shows the sialic acid aqueous solution treated in Experimental example 1 of the present invention after being left at room temperature for 2 years;
FIG. 2 shows the sialic acid aqueous solution treated in comparative example 1 of the present invention after storage at room temperature for 2 years
FIG. 3 shows the sialic acid solution treated in example 2 of the present invention after being hermetically placed at 80 ℃;
FIG. 4 shows the sialic acid solution of comparative example 2 after treatment at 80 ℃ in a sealed state;
FIG. 5 shows the sialic acid solution treated in example 3 of the present invention after being hermetically placed at 60 ℃
FIG. 6 shows the sialic acid solution treated in comparative example 3 of the present invention, which was hermetically placed at 60 ℃.
Detailed Description
The following examples are given to further illustrate the embodiments of the present invention. The following examples are provided to illustrate the present invention, but are not intended to limit the scope of the present invention.
The raw material components used in the invention can be obtained commercially, and the reagents used in the embodiment of the invention are all chemically pure.
The preparation method of sialic acid used in the embodiment of the invention is the method disclosed in embodiment 4 of CN201811372637.8, and specifically comprises the following steps:
filtering 25g/L polysialic acid fermentation liquor by using a 200nm ceramic membrane, and then filtering by using an ultrafiltration membrane with the specification of 11KDa until the solid content of the solution is less than 3 times of the content of the polysialic acid to obtain a polysialic acid solution. Adding sulfuric acid into the polysialic acid solution until the pH value of the solution is 1, and reacting for 3.0h at the temperature of 86 ℃ to obtain the sialic acid solution. Adding activated carbon with the mass ratio of 2% to the sialic acid solution into the sialic acid solution for decolorization to obtain a decolorized solution, adding sodium hydroxide until the pH of the solution is 5 to obtain a sialic acid salt solution, and filtering the decolorized solution by using an ultrafiltration membrane of 1.2KDa to remove unhydrolyzed polysialic acid. And filtering the sialic acid salt solution by adopting a 350Da nanofiltration membrane to obtain a nano-filtrate, wherein the solid content in the nano-filtrate is less than 3 times of the sialic acid content. And (3) concentrating the nanofiltration liquid by vacuum heating, adding 33% perchloric acid until the pH value of the solution is 2, crystallizing at 6 ℃ for 8 hours to obtain crystals, and filtering and vacuum drying the crystals to obtain the sialic acid.
The invention is described in detail with respect to the sialic acid obtained in example 4 in CN201811372637.8, and the sialic acids obtained in other embodiments disclosed in CN201811372637.8 are consistent with the results of the sialic acid obtained in example 4, and are not described in detail in the invention.
The obtained sialic acid was dissolved in water to prepare aqueous sialic acid solutions having different concentrations in the following examples.
Example 1
Preparing a 2% sialic acid aqueous solution, adjusting the pH value to 2.0, then adjusting the pH value of the sialic acid aqueous solution to 7.0 by using sodium hydroxide, and sealing and placing in a normal-temperature environment. The color of the product is not changed after the product is placed for 2 years.
Example 2
Preparing 5% sialic acid water solution with pH of 1.8, adjusting the pH value of the sialic acid water solution to 8.0 with potassium hydroxide, and sealing and placing in an environment at 80 ℃.
Example 3
Adjusting pH of N-acetylneuraminic acid aqueous solution to 9.0 with alkaline substance such as sodium hydroxide or sodium carbonate, sealing and standing at 60 deg.C.
Comparative example 1
Comparative example 1 is the same as example 1 except that sodium hydroxide was not used to adjust the pH of the aqueous sialic acid solution.
Comparative example 2
Comparative example 2 is the same as example 2 except that potassium hydroxide was not used to adjust the pH of the aqueous sialic acid solution.
Comparative example 2
Comparative example 3 is the same as example 3 except that an alkaline substance such as sodium hydroxide or sodium carbonate is not used to adjust the pH of the aqueous sialic acid solution.
The aqueous sialic acid solution of example 1 was left for 2 years without discoloration as shown in fig. 1, whereas the aqueous sialic acid solution of comparative example 1 became pale yellow at about 6 months of standing as shown in fig. 2.
The aqueous sialic acid solution of example 2 was left for 6 months without changing color as shown in FIG. 3, whereas the aqueous sialic acid solution of comparative example 2 changed to light yellow at day 5, and then gradually deepened color as shown in FIG. 4.
The aqueous sialic acid solution of example 3 was left for 12 months without changing color as shown in FIG. 5, whereas the aqueous sialic acid solution of comparative example 2 changed to light yellow at day 15, and then gradually deepened color as shown in FIG. 6.
Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A method for preventing discoloration of an aqueous sialic acid solution, comprising the steps of:
adjusting the pH value of a sialic acid aqueous solution to 6.0-8.0, wherein the sialic acid aqueous solution is prepared by dissolving sialic acid in water; the sialic acid is at least 80% pure.
2. The method of claim 1, wherein the sialic acid is extracted by adjusting the pH of a sialic acid solution obtained by pretreating a sialic acid monomer source, concentrating and purifying, heating and concentrating, and performing acidification and crystallization; the sialic acid monomer source is polysialic acid or cubilose.
3. The method of claim 2, wherein the source of sialic acid monomers is polysialic acid and the pre-treatment is hydrolysis; the hydrolysis reaction of the polysialic acid comprises the following steps: and adding an acid substance into the polysialic acid until the pH value of the solution is 1-2, and reacting for 2-4 hours at the temperature of 80-90 ℃.
4. The method of claim 1, wherein the aqueous sialic acid solution has a concentration of 1% to 20%.
5. The method of claim 4, wherein the aqueous sialic acid solution has a concentration of 2% to 5%.
6. The method according to any one of claims 1 to 5, wherein the aqueous sialic acid solution is adjusted to a pH of 6.0 to 8.0 using an alkaline reagent; the alkaline reagent is sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.
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