Process intensification of seaweed biorefinery using reusable natural deep eutectic solvents

Conventional alginate extraction methods from brown seaweed typically rely on harsh chemicals that are not reused, and valuable pigments are lost during this process. This study applied a novel approach utilising reusable natural deep eutectic solvents (DES) in three-phase partitioning (TPP) to simultaneously extract alginate and pigments from Saccharina latissima . The hydrophobic DES effectively released alginate from the algal cell wall in the aqueous phase and served as a solvent for pigment extraction. Computational screening confirmed that all selected DES had an affinity for pigments chlorophyll a and fucoxanthin, while alginate extraction confirmed their role in disrupting the algal cell wall. Extraction conditions were optimised, resulting in an alginate yield of 101.8 ± 3.1 mg/g DW compared to 55.3 ± 14.1 mg/g DW for conventional alkaline extraction. According to physicochemical characterisation through FT-IR and M/G ratio (mannuronic to guluronic) analysis, the extracted alginate was comparable to that obtained via alkaline extraction, exhibiting similar functional groups and M/G ratios. The DES was reused successfully, showing that it could be reused for up to seven extraction cycles, during which pigments accumulated. After the seventh cycle, alginate yield declined, likely due to partial transfer into the DES phase, possibly driven by reverse micelle formation in the system. This study highlights a novel, mild multiproduct approach of a DES-based TPP system, enhancing economic feasibility by employing gentler and quicker extraction conditions. It facilitates the concurrent recovery of alginate and pigments while allowing for the repeated reuse of the DES.