Disruption or partitioning? Deep eutectic solvent biphasic systems for integrated seaweed biorefineries

In this study, a DES-based biphasic system (FABU) was evaluated for the multiproduct extraction of compounds from Saccharina latissima. The system combined a hydrophobic fatty-acid phase (dodecanoic acid-octanoic acid, FA) for fucoxanthin extraction with a hydrophilic betaine-urea-phase (BU) for alginate recovery, together with citric acid pretreatment for fucoidan and mannitol recovery. While fucoxanthin partitioning into the FA phase was limited (41-58 µg g^- 1), a substantially higher fucoxanthin concentration (563 ± 8 µg g^- 1) was recovered during the subsequent alkaline extraction step. This behaviour indicates that the DES-based system likely acts as a medium that enhances biomass permeability rather than directly promoting partitioning. Chromatographic profiles further showed enhanced fucoxanthin preservation relative to conventional pigment extraction, suggesting a protective role of the DES matrix. These findings highlight a decoupling between biomass disruption and solubilisation in DES-based systems. Our research shows new opportunities to deploy biphasic DES systems as powerful pretreatment platforms within integrated seaweed biorefineries, thereby offering a new strategy for preserving and recovering sensitive compounds.