Cultivation Of Scenedesmus Sp.-BH Separated From North Lake In Shihezi And Antioxidant Activities Of Its Polysaccharides

Microalgal polysaccharides, especially microalgal sulfated polysaccharides, have strong antioxidant,antiviral, antitumor, and improve immunity activities. Brown and red algae with characteristics of largevolume and ease of harvesting have been studied widely and deeply, while researches of green algae livingin the plant phylogenetic tree trunk status are relatively few. One miroalga named Scenedesmus sp.-BHwith the characteristic of self-flocculation was separated and isolated from lakes and rivers in Xinjiangfreshwaters. Then the culture medium and extraction teqnique of polysacchaeides from Scenedesmus sp.-BH were optimized and the antioxidant activities of crude polysaccharides were studied. Results are asfollows:The microalgae used in this research were isolated from freshwaters in Xinjiang, China with the spreadplate method. According to the morphological characteristics, including cell size, shape, and chloroplastcore protein number, they were named as Chlorella sp.-YL, Scenedesmus sp.-BH, Schroederia sp.-90andMicrocystis sp.-W, respectively. All cultures were unialgal and conducted in the basal BG11medium. Thebiomass and IPS production of Scenedesmus sp.-BH were approximately250.5and5.55mg/L, more thanthe other three microalgae. The flocculation efficiency could reach up to92.29%after12h standing.To improve the biomass and IPS production of Scenedesmus sp.-BH, uniform design was applied tooptimize the critical medium components of NaNO₃, K₂HPO₄·3H₂O, MgSO₄·7H₂O, ferric ammoniumcitrate, and NaHCO₃in a batch culture at laboratory scale. Using stepwise regression analysis, the modelpredicted the maximum biomass yield of579.75mg/L, appeared at NaNO₃0.77g/L,K₂HPO₄·3H₂O0.24g/L, MgSO₄·7H₂O0.24g/L, ferric ammonium citrate0.021g/L, and NaHCO₃3.85g/L, while a maximumIPS yield of14.58mg/L appeared at NaNO₃0.004g/L,K₂HPO₄·3H₂O0.24g/L, MgSO₄·7H₂O0.21g/L,ferric ammonium citrate0.024g/L, and NaHCO₃1.42g/L. When applying these optimal mediumcomponents, the maximum biomass556.7±16.97mg/L and WSIP production14.3±0.46mg/L weredemonstrated by confirmatory experiments. They were both more two fold than those cultured under theoriginal conditions.To improve the extraction yield of Scnedesmus sp.-BH polysaccharides, on the basis of single-factortests, alkali concentration, extraction temperature, and extraction time affecting the extraction yield ofScnedesmus sp.-BH polysaccharides were optimized by using response surface methodology （RSM）. Theresults showed that the optimum alkali concentration, extraction temperature, and extraction time ofScnedesmus sp.-BH polysaccharides extraction were0.175mol/L,80.8°C and2.1h, respectively. Underthese conditions, the experimental extraction yield of Scnedesmus sp.-BH polysaccharides was up to11.08%, which matched well with the predicted yield of10.91%. The extraction yield of Scnedesmus sp.-BH polysaccharides with the optimized alkali extraction was higher than the value with hot waterextraction by4.7times.In order to determine the antioxidant activity of Scenedesmus sp.-BH polysaccharide in vitro,Scenedesmus sp.-BH crude polysaccharides were used to scavenge free groups of OH· and DPPH· andcomplex ferrous ion. Within the given concentrations, the antioxidant activities of Scenedesmus sp.-BHpolysaccharides were enhanced with the increase of the concentration of the polysaccharides. When theconcentration of Scenedesmus sp.-BH was1000μg/mL, the scavenging effect of OH· and DPPH· were61.88%and58.42%, respectively; of the ferrous ion complex capacity was87.16%. It was demonstratedthat Scenedesmus sp.-BH polysaccharides had good antioxidant activities.