Study On The Isolation And Purification Of Polysialic Acid And Sialic Acid From Fermentation Broth

Sialic acid (SA) is a kind of carbohydrate compounds that consist in biological system widely. Sialic acids play an important role in the process of biochemical and physiological processes of many organisms. Polysialic acid (PSA) is a bacterial capsular homopolysaccharide of N-acetylneuraminic acid (NeuAc) withα-(2, 8) and / orα-(2, 9) ketosidic linkages. Polysialic acid can be produced by fermentation, and polysialic acid can be hydrolyzed into sialic acid. Sialic acids and its derivatives were obtained after purification and conversion by chemical and enzymatic methods.Fed-batch fermentation of polysialic in 50L semi-automatic fermentor acid was investigated. The polysialic acid yield reached 2800 mg/L finally.Extraction process of polysialic acid from fermentation broth was optimized. Ethanol precipitation was combined with alkaline filtration. The processes were as follows: 4%NaCl was dissolved into fermentation broth before precipitation with ethanol that was 3 times of liquid volume. The precipitate was dissolved with distilled water. The PSA solution was filtered with perlite as filtration aid. The filtration was repeated with perlite after pH of filtrate was adjusted to 10.0. The filtrate was adjusted to 7.0 at last. As a result, the removal of protein was 91.2% and the recovery was about 85.4%.Polysialic acid (PSA) could form complex with cetyl pidinium chloride (CPC) specifically and was thus used for the separation of PSA from E. coli fermentation broth. The optimal conditions of completely complex reaction between CPC and PSA were obtained by single-factor experiment: NaCl 0.05mol/L, pH 6.0 and CPC/PSA (w/w) =3. And the optimal conditions for PSA-CPC complex dissociation were as follows: NaCl≤0.1mol/L and 50℃in water bath. The purity of PSA recovered by CPC treatment was higher than 95% and the yield of PSA was above 80%. The PSA purity and structure was also confirmed by FT-IR analysis.High-purity polysialic acid was hydrolyzed into sialic acid, after decolorization and crystallization, the purity of the sialic acid product was above 90%.