Isolation and structural characterization of sulfated polysaccharide from Spirulina platensis and its bioactive potential: In vitro antioxidant, antibacterial activity and Zebrafish growth and reproductive performance

In this study, the sulfated polysaccharide (SPs) was isolated from Spirulina platensis. The isolated SPs contains carbohydrate, sulfate, protein and uronic acid at 38.7 ± 0.30%, 21.3 ± 0.87%, 7.1 ± 0.15% and 7.9 ± 0.4% respectively. The elemental analysis confirmed the presence of carbon (18.01 ± 0.10%), hydrogen (1.83 ± 0.02%) and nitrogen (3.43 ± 0.01%). The monosaccharide composition and molecular weight of SPs were analyzed by high-performance liquid chromatography and size exclusion chromatography respectively. The monosaccharide composition analysis showed the existence of glucose, rhamnose, xylose, fucose, mannose, galactose and the molecular weight of SPs was 1016 kDa. Further, the characterization of SPs was done by UV–visible spectroscopy, X-ray diffraction, FT-IR, 1H NMR and 13C NMR analysis. The obtained SPs exhibited potent antioxidant activity in DPPH (76.45 ± 0.49%), reducing power (absorbance: 1.3 ± 0.02), hydrogen peroxide scavenging (66.3 ± 1.16%), hydroxyl scavenging (68.6 ± 3.2%), nitric oxide (81.36 ± 1.85%) and total antioxidant (absorbance:1.66 ± 0.02) activities at 5 mg/ml. In addition, SPs revealed the highest antibacterial efficacy against the pathogenic bacteria Vibrio vulnificus in disc diffusion, agar bioassay and protein leakage assays at 100 μg/ml. Furthermore, the supplementation of 2% SPs through a feed to the Danio rerio fish enhances the growth and reproductive performances. This finding confirmed that the isolated SPs from S. platensis possess pharmaceutical as well as nutritional properties.