Posidonia oceanica , a Mediterranean seagrass, represents a promising marine resource for the production of high-value polysaccharides with potential industrial and biomedical applications. In this study, ultrasound-assisted extraction (UAE) was deliberately applied under non-optimized conditions to investigate its impact on the structure of polysaccharides obtained from P. oceanica leaves (MKF) and rhizomes (MKR), yielding 0.63% and 0.43% ( w /w), respectively. GC–MS analysis of MKF revealed a diverse monosaccharide profile, including xylose (22.7%), arabinose (21.7%), glucose (16.3%), rhamnose (13.2%), and, for the first time in Posidonia oceanica , tentatively identified talose (7.2%), lyxose (7.7%), and fucose (4.0%). Molecular weight determination via size-exclusion Chromatography showed 394,000 g·mol −1 for MKF and 180,000 g·mol −1 for MKR. Leaf-derived polysaccharides exhibited significantly stronger antioxidant activity (DPPH IC₅₀ = 10.91 ± 0.70 μg/mL; ABTS IC₅₀ = 6.78 ± 0.07 μg/mL) compared to rhizome extracts. Both extracts demonstrated high photoprotective potential (SPF = 42.3 and 39.3 for MKF and MKR, respectively) and substantial antiviral potency toward type 2 herpes simplex virus, with selectivity indices of 750–850 and no detectable cytotoxicity up to 2500 μg/mL. These results suggest that ultrasound-induced structural modifications enhance the bioactivity of P. oceanica polysaccharides, positioning them as multifunctional biomolecules with potential applications in pharmaceuticals, cosmeceuticals, and other industrial sectors.
Malaoui et al. (Fri,) studied this question.