In vitro antioxidant activity and cytotoxic effects of sulfated galactan polysaccharides from Gracilaria spinulosa

This study investigated the extraction, chemical composition, structural characteristics, antioxidant activity, and in vitro cytotoxic potential of sulfated galactan polysaccharides (SGP) isolated from the red seaweed Gracilaria spinulosa collected from the Gulf of Mannar, Tamil Nadu, India. SGP was extracted using an acidic hot-water extraction method with a yield of 7.2%. Chemical characterization revealed that the polysaccharide contained 68.2% total carbohydrates, 20.6% sulfate, and 4.0% ash, with galactose (78.2%) as the predominant monosaccharide. Fourier-transform infrared (FTIR) spectroscopy confirmed the presence of characteristic sulfate ester functional groups, while scanning electron microscopy (SEM) revealed irregular particles with well-defined rectangular microstructures. The extracted SGP exhibited moderate antioxidant activity in DPPH and superoxide radical scavenging assays. Cytotoxicity evaluation demonstrated that SGP produced concentration-dependent inhibition of HT-29 human colon adenocarcinoma cells with an IC₅₀ value of 64.22 ± 0.67 µg/mL, while showing no significant cytotoxicity toward normal human colon epithelial cells (CCD-841) under the tested conditions. These findings demonstrate that G. spinulosa -derived SGP possesses in vitro antioxidant and selective cytotoxic potential.