Valorization of Beach-Cast Biomass from the Invasive Seaweed Rugulopteryx okamurae on the Moroccan Coast: A Comparative Assessment of Extraction Conditions for Sodium Alginate Recovery

Rugulopteryx okamurae is an aggressively invasive seaweed whose proliferation along the Moroccan coastline represents both an ecological problem and an underexploited source of biomass. This work highlights the isolation of sodium alginate from R. okamurae under four combinations of acid pretreatment and alkaline (carbonate) extraction conditions. The extracted alginates were characterized by determining the extraction yield and analyzing their structural features using Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). Alginate yields ranged from 11 to ~16% (dry weight), and the highest yield 15.85 ± 0.66% dw was obtained with acidification treatments of 2 h at 40 °C and alkaline extraction at 60 °C over 5 h. FTIR analysis confirmed the sodium alginate structure and suggested the absence of detectable sulfate polysaccharide (fucoidan) contamination, as evidenced by the absence of a S=O band. 1H NMR analysis revealed a guluronate rich polymer within the four used protocols, highlighting its potential to form a strong and rigid gel. The present study highlights the alien R. okamurae as a viable source of high guluronate sodium alginate and clarifies how extraction conditions might shape its yields.