| Eustigmatos magnus is a soil microalga belonging to Eustigmatophyceae. Previousstudies have comfirmed that low nitrogen conditions promote the oil accumulation butinhibit the growth of microalga. So it is the most important job that choosing anoptimal concentration of sodium nitrate for the growth and oil production ofmicroalga. Otherwise, microalga polysaccharides have caused an emerging interest inthe biomedical area, due to their structural diversity and bioactivities.The cost of biodiesel production can be decreased through development andutilization of such high-value-added product from microalga. The effects of sodiumnitrate concentration on the morphology, biomass, total lipid content, lipid fraction,fatty acid composition, volumetric productivity of total lipid and netural lipid of E.magnus, which was cultured in the column photobioreactors (3cm in diameter) withthe BG-11medium were investigated with the purpose to reveal the laws of oilaccumulation. Using vertical flat plate glass photobioreactors (4cm in diameter) tocultivate E. magnus with the BG-11medium under the sodium nitrate concentrationof6mmol/L. Biomass, total lipid content, lipid fraction were also tested in order toknow whether the alga can keep the high oil productivity under the condition ofrelatively extensibe cultivation. Three polysaccharide fractions were separated fromthe extracts of the defatted algae residue. The physicochemical properties such asglucosidic bond and monosaccharides composition were investigated. The mainresults were as following:(1) The optimum sodium nitrate concentration for the growth of E. magnus was9mmol/L and the highest biomass was11.31g/L. Neutral lipid, glycolipid andphospholipid were partitioned from total lipid of this alga through C18cartridge.Under the sodium nitrate concentration of3.6mmol/L, the total lipid content reached60.21%(%dry weight) and the neutral lipid content reached55.98%(%dry weight)(92.99%,%total lipid). All of the values were higher than the other three groups. Inaddition, the main components of fatty acid were palmic acid, palmitoleic acid and oleic acid, while the sum of their contents achieved55%to87%(%total fatty acid).The optimal concentration of sodium nitrate for the volumetric productivity of totallipid was9mmol/L and the value was up to0.29g/L/d, meanwhile the maximumvolumetric productivity of neutral lipid ran up to0.26g/L/d under the concentrationof6mmol/L.(2) The biomass of E. magnus reached4.91g/L using vertical flat plate glassphotobioreactors under the sodium nitrate concentration of6mmol/L. Total lipidcontent was46.68%(%dry weight). The neutral lipid content was39.5%(%dryweight) and83.38%(%total fatty acid). The volumetric productivity of total lipidwas0.13g/L/d while the volumetric productivity of neutral lipid was just0.11g/L/d.(3) The crude polysaccharides were seperated and purified. Three main fractions,named EM-1, EM-2and EM-3respectively, were obtained. The characterizations,such as monosaccharides composition and infrared spectrum of the three fractionswere analyzed. The results indicated that all of the three fractions had a backbone ofα-conformation. EM-1consisted of ribose, rhamnose, arabinose, xylose, mannose,glucose and galactose. The content of xylose and galactose reached more than60%.EM-2contained arabinose, xylose, mannose, glucose and galactose, no ribose andrhamnose. Glucose, mannose and arabinose were top three monosaccharides. EM-3has the same monosaccharides composition as EM-1, but the content of xyloseachieved more than50%. |
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