Optimization of an Eco-Friendly Extraction to Obtain Monosaccharides from the Invasive Macroalga Rugulopteryx okamurae

Background: The invasive macroalga Rugulopteryx okamurae poses severe environmental challenges but presents an opportunity as a sustainable source of valuable carbohydrates. This study develops an eco-friendly method to extract monosaccharides from this biomass. Methods: Ultrasound-assisted extraction (with sonotrode) using water as the solvent was optimized with Design of Experiments, and the time, power and mass:solvent ratios were evaluated. The monosaccharide composition was evaluated by gas chromatography coupled to high-resolution mass spectrometry (GC-QTOF). Results: The analytical method was validated for accurate monosaccharide quantification using oximes and silylation, achieving a fast time of analysis (<20 min). The optimized UAE (1:15 mass:solvent ratio, 70% power, 30 min) yielded a total monosaccharide concentration of 210 mg mL−1, significantly outperforming traditional acidic hydrolysis. Compared to the extraction of monosaccharides from the well-known seaweed Ulva ohnoi (31 mg mL−1), it is far superior. Mannitol comprised 95% of the total extract. Conclusions: This scalable and green UAE methodology valorizes this seaweed by achieving high yields of simple sugars, offering a sustainable resource for industrial applications while mitigating the environmental impact of this invasive species.