Potential use of Sargassum muticum as source of plant biostimulants after three different drying methods

Seaweed derived biostimulants are gaining attention as an important tool in sustainable agriculture. This offers a unique opportunity to alleviate the environmental impact of Sargassum muticum (Ochrophyta, Phaeophyceae) as an invasive species by finding new applications for its biomass. In this sense, incorporating green extraction technologies is fundamental to ensure environmental-friendly goals. This research was initiated in an attempt to contribute to an integral valorization system of S. muticum biomass, exploring the biostimulant potential of the solubles obtained from pressed solids, through an autohydrolysis treatment. In addition, we compared the effect of three different liquid phase drying techniques (spray-drying, freeze-drying and convective air-drying). Low stress drying techniques as spray-drying showed better conservation of bioactive compounds and biostimulant potential. A bioassay with Nastrium officinale showed no phytotoxic effects despite high electric conductivity in most of the extracts and concentrations. Dried extracts showed mainly an amorphous structure but occasional crystal formation when spray-dried at low temperatures (T-out = 50 oC) and after convective air drying (T = 40 oC). Significant increases in root development were achieved at a concentration of 5 mg L-1 of spray-dried extracts and 50 mg L-1 in case of freeze-dried extracts. Munoo-Liisa vitality index showed best results with 50 mg L-1 of freeze-dried extracts. This study provides important information about the influence of different drying techniques on the physicochemical properties and biostimulant potential of S. muticum aqueous extracts and contributes to the integral valorization of its biomass.