Ultrasound-assisted valorization of posidonia oceanica polysaccharides; discovery of novel monosaccharides and enhanced multifunctional bioactivity

Posidonia oceanica, a Mediterranean seagrass, represents a promising marine resource for the production of highvalue 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 sizeexclusion 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.