Evaluation of sustainable technologies for the processing of Sargassum muticum: cascade biorefinery schemes

Abstract

The leverage of invasive macroalgae, which represent a serious threat for autochthonous biodiversity, may smooth and mitigate their risk from an environmental point of view while providing an economic benefit. This work proposes the suitability of a closed loop biorefinery employing sustainable technologies (namely autohydrolysis, ultrasound assisted extraction, and microwave hydrodiffusion and gravity) for the complete exploitation of the invasive brown macroalgae Sargassum muticum. In particular, sequential extraction methods allowed recovery up to 85% of fucoidan in the form of sulfated fucooligosaccharides in the liquid phase, besides increasing the phloroglucinol and Trolox equivalent antioxidant capacity (TEAC) content up to 9.73 g per 100 g of extract and 31.1 g per 100 g of extract, respectively. Additionally, extract-free Sargassum muticum presented a high enzymatic susceptibility at a high solid loading, implying a production of 15.6 g ethanol per L (91.9% of ethanol yield) in SHF, while the resulting spent solid provided a calorific power of 10.0 MJ kg⁻¹. This work verified the cascade biorefinery employing sustainable technologies as an appropriate strategy for the integral valorization of Sargassum muticum.