Separation And Purification Of Water-Soluble Polysaccharides From Cyanobacteria In Tai Lake

Cyanobacteria in Tai Lake, mainly composed of Microcystis aeruginosa, Anabaena flos-aquae and Aphanizomenon flos-aquae, is one of the main pollutants in Tai Lake in summer. However, the polysaccharides, proteins and other components contained in cyanobacteria are valuable bio-active components. The successful separation of them from cyanobacteria is therefore significant for changing the waste to valuable materials. In this study, the separation of water-soluble polysaccharides from cyanobacteria in Tai Lake has been investigated systematically and the following conclusions could be drawn:1. The extraction efficiency of total sugar content was studied using mixture of concentrated hydrochloric acid(HCl) with water(H2O) as digestion reagent. It is demonstrated that when digested for 4 hr at 100℃in a mixture of H2O/HCl(volume ratio)=33:1 the total sugar content in dry Cyanobacteria is measured to be 10.79%. Further analysis using thin layer chromatography(TLC) showed that the monosaccharide components in hydrolyzed product were glucose, rhamnose, arabinose or mannose, etc.2. Compared with the extratiion using hot water and via freeze-thaw method, the yield of polysaccharides is approximately equal, but using hot water extraction could reduce extraction time and use sinple equipments. By means of orthogonal tests the optimal extracting conditions using hot water to extracte water-soluble polysaccharides from cyanobacteria were obtained: solution(mL)/material(g)=30:1, extracting temperature 80℃, extracting time 4 h. The yield of polysaccharides at this condition was 56.24%.3. The hot water extract, water-soluble polysaccharides, from cyanobacteria was separated and purified by removing impurities via flocculation. As flocculation agents, PAC, WCK, and PFS were found to be effective while polypropylene amine shuch as cPAM, nPAM, aPAM were ineffective. Moreover the combination of PFS and PAMs can not enhance flocculation efficiency. With PFS as flocculant at an addition amount of 500 mg/L the viscosity of extract can be reduced by 41.10%. The flocculation rate, decolorization rate, protein removal rate, as well as the total sugar recovery were 80.32%, 75.48%, 50.30% and 85.40%, respectively. The pH value as well as temperature shows no influence. The purified polysaccharides were obtained as precipiteates from the flocculated aqueous solution by adding alcohol three times volume of solution. The purity of redissolved polysaccharides reaches 86.01%. HPGPC test indicates that there are three kinds of sugars in this solution, the relative molecular mass(Mp) respectively for 1.46 million, 0.43 million and 1,767. The investigation of Zeta potential found that PFS can neutralize the surface charge on the impurities and stimulate the agglomeration of floc. The morphology revealed that the formation and agglomeration of floc normally finishes in 5 min.4. The impurities in the precipitate were removed further by dissolving the precipitate in water followed by adsorption using resins. The study indicats that ADS-7 resin shows a higher adsorption capacity and selectivity to protein and other impurities than AB-8, D101, D315, HPD100, and S-8 resins, and the recovery of polysaccharide is high. The optimized static adsorption condition is adding 1 g resin to 40 mL of aqueous solution of the precipitate containg 5 mg/mL polysaccharide at pH=6 followed by vibrating the mixture at 35℃for 6 hr. In this condition, 73.17% of the impurities can be removed and a polysaccharide recovery as high as 91.90% can be reached. The purity of polysaccharides finally obtained reaches 95.46%. The optimized dynamic adsorption conditions were: 16 BV of 5 mg/mL polysaccharide aqueous solution at pH=6, at a flow rate of 2BV/h. In this condition the protein removal rate, adsorption ratio of impurities, polysaccharide recovery and the purity of polysaccharides are 85.01%, 82.33%, 98.10% and 97.14%%, respectively. The ADS-7 resin shows a high adsorption and selectivity. Moreover, the ADS-7 resin has a steady performance and a good reusability, which is suitable for large-scale of production. HPGPC test indicates that there are two kinds of solution of sugars, the relative molecular mass(Mp) respectively for 1.44 million and 0.42 million.