Quantitative methods for transforming macroalgal polysaccharides into fermentable sugars: Composition and insights for industrial algal bioprocessing

Macroalgae represent a sustainable marine bioresource with significant potential as renewable feedstocks for bioprocessing applications, including pharmaceuticals, food additives, and biofuels. However, most studies focus on single species or hydrolysis routes without linking composition to fermentation-ready sugar concentrations. This study presents a comprehensive compositional analysis of nine European seaweed species (eight brown and one red alga) selected for their industrial relevance, and evaluates optimized hydrolysis strategies to maximize fermentable monosaccharide yields, using L. hyperborea as the model species for bioprocessing applications. Total monosaccharide yield reached 64.59 % DW in L. digitata and 63.81 % in L. hyperborea . Monosaccharide profiles revealed distinct, species-dependent patterns, with kelp species enriched in uronic acids and glucose, Fucus spp . characterized by elevated mannitol and fucose levels, and the red alga Gelidium corneum is dominated by galactose. Hydrolysates achieved glucose concentrations of up to 17 g/L, surpassing typical thresholds required for efficient microbial fermentation and bioprocessing. Elemental analysis with ICP-MS indicated low toxic metal content (arsenic, lead, cadmium), supporting the suitability of these hydrolysates as substrates for microbial cultivation. Mass balance analysis accounted for 60%–90% of biomass components, indicating the presence of unquantified compounds that may affect process efficiency. Collectively, this study presents the first cross-species, process-oriented compositional dataset that integrates carbohydrate and elemental analyses, providing a quantitative foundation for selecting seaweed feedstocks and hydrolysis strategies in industrial bioprocessing. • Compositional analysis of nine seaweed species with monosaccharide and elemental compositions among others. • Hydrolysis optimisation achieved bioprocessing-grade glucose concentrations. • Seaweed hydrolysates directly usable in industrial bioreactors. • Scalable method proposed for industrial seaweed biomass valorisation. • Seaweed positioned as sustainable second-generation bioprocessing feedstock.