Physicochemical properties and bioactivity of polysaccharides from Sargassum pallidum by fractional ethanol precipitation

Summary Three polysaccharides (SPP‐30, SPP‐60 and SPP‐90) were fractionated from Sargassum pallidum by 30%, 60% and 90% (v/v) ethanol, successively. Their physicochemical properties, antioxidant and antibacterial activities of SPP‐30, SPP‐60 and SPP‐90 were comparatively investigated. The results showed that three polysaccharide fractions contained different neutral sugar, protein, uronic acid and sulphate contents. SPP‐30 had the highest molecular weight (3.77–206.73 kDa), followed by SPP‐60 (5.55–189.44 kDa) and SPP‐90 (4.92 kDa). SPP‐30, SPP‐60 and SPP‐90 were composed of fucose, arabinose, galactose, glucose, xylose and mannose but with different molar ratios. Scanning electron microscopy analysis suggested that they had different surface morphology and sizes of fragmentation. In vitro antioxidant assays suggested that SPP‐30 and SPP‐90 exhibited stronger scavenging activities against DPPH, ABTS and hydroxyl radicals than SPP‐60. Moreover, SPP‐30 and SPP‐60 exhibited antibacterial activities against Staphylococcus aureus , while SPP‐90 exhibited moderate antibacterial activity against both Staphylococcus aureus and Escherichia coli .