Biorefinery approach to valorize Sargassum muticum: Autohydrolysis pretreatment for oligosaccharides, bioethanol, and biosuccinic acid production

The brown macroalga Sargassum muticum (Sm) is an invasive species originating from Japan and China which has spread extensively across the globe since the 19 th century. This work evaluates autohydrolysis as a pretreatment strategy to obtain a liquor rich in oligosaccharides and antioxidant compounds, along with a solid fraction with high enzymatic susceptibility suitable for fermentative valorization. The highest oligosaccharide yield in the liquor was 8.38 g per 100 g of dry Sm at severity of 2.67 (maximum temperature of 170 °C), with approximately 50% derived from fucoidan hydrolysis. Under these conditions, the phenolic and flavonoid content was found to be 14.46 mg GAE/g Sm and 16.16 mg QE/g Sm, respectively. The antioxidant capacity was evaluated using various assays, yielding 27.75, 6.80, and 18.46 mg TE/g Sm for ABTS, DPPH, and FRAP, respectively, while total antioxidant capacity (TAC) assay reached 47.35 mg AAE/g Sm. Enzymatic hydrolysis of the recovered solid at the same severity, performed in fed-batch mode, produced 47.65 g/L of glucose. This hydrolysate was used in two separate fermentation processes: one producing 21.48 g of bioethanol/L and another yielding 22.75 g of biosuccinic acid/L. These results support the potential of Sm as a promising feedstock in a biorefinery context. Its valorization not only enables the production of bio-based chemicals but also offers an opportunity to economically exploit an invasive and underutilized species. • Autohydrolysis was applied to valorize the invasive macroalga Sargassum muticum. • Oligosaccharide yield reached 8.38 g/100 g at optimal severity (S₀ = 2.67). • Antioxidant capacity, TPC and TFC were evaluated in the solubilized liquor. • Fed-batch enzymatic hydrolysis yielded 47.65 g/L of glucose. • Bioethanol (21.48 g/L) and biosuccinic acid (22.75 g/L) were obtained via fermentation.