Abstract: Different fractions S1 ,S2 and S3 of Spirulina platensis raw polysaccharides were got by fractionation with cetyltrimethylammonium bromide (CTMAB) and ethanol. The SL1 SL2 and SL3 of sulfated polysaccharides were synthesized by modification with sulfuryl chloride. Sulfuric group content was determined by means of BaCl2-glutin turbidimetry. Some strong characteristic absorption peaks of ester sulphate bonds were observed at 1 240 cm-1, 810 cm-1 and 620 cm-1 respectively by FTIR. Fenton reaction was used as a producing hydroxyl radical model and the capacities of different fractions of sulfated polysaccharides for scavenging OH were compared with those of the unsulfated. Results demonstrated that there was a great difference for the scavenging OH capacities due to the differences of fraction, composition, polarity and acidity of polysaccharides. The order of capacity for scavenging hydroxyl radical was as follows; S1 > S3 > S2. The capacities of sulfated fractions SL2 and SL3 for scavenging OH were much stronger than those of the unesterified Spirulina platensis polysaccharides S2 and S3.

Key words: Spirulina platensis, polysaccharide, chemical modification, hydroxyl radical