Bioactive Potential of the Sulfated Exopolysaccharides From the Brown Microalga <i>Halamphora</i> sp.: Antioxidant, Antimicrobial, and Antiapoptotic Profiles

This study aims to investigate the physicochemical characteristics of the exopolysaccharides (EPS) extracted from the microalgae species <i>Halamphora</i> sp., as well as to evaluate their antioxidant, antibacterial, and anti-apoptotic activities. The crude extracellular polysaccharides from the halophilic diatom <i>Halamphora</i> sp. were found to be extracellular heterosulfated anionic polysaccharides containing carbohydrates (76.33 ± 1.80%), proteins (0.15 ± 0.02%), uronic acids (5.44 ± 0.08%) and sulfate (7.56 ± 0.86%). The lowest protein (0.24%) and lipid (0.15%) contents suggested that EPS was highly pure. Gas chromatography-mass spectrometry analysis revealed that the carbohydrate fraction consisted of xylose, l-galactose, d-galactose, glucose, ribitol, mannose, and inositol with corresponding mole percentages of 40.55, 13.25, 13.00, 9.95, 9.82, 2.90, and 2.28, respectively. In vitro, tests showed a high total antioxidant capacity probably related to l-galactose followed by d-galactose, uronic acid, and ribitol. In addition, extracellular polysaccharides (EPS) demonstrated effective antimicrobial Gram + properties with inhibition zones ranging from 10 to 12 mm. Molecular docking showed an antiapoptotic effect, as the best docking score was generated due to the interaction of xylose and caspase 3 (-6.9 kcal/mol) and l-galactose and caspase 3 (-5 kcal/mol). Overall, the findings of this study suggest the possibility of using the EPS extract of <i>Halamphora</i> sp. as an additive for nutraceutical and cosmetic purposes.