Simultaneous extraction and stabilization of fucoxanthin using a hydrophobic antioxidant deep eutectic solvent

The recovery of labile marine bioactives such as fucoxanthin from Sargassum sp. is constrained by oxidative and thermal degradation during processing. Herein, a hydrophobic antioxidant deep eutectic solvent (DES) composed of thymol (Thy) and methyl salicylate (MeSA) was developed for the simultaneous extraction and stabilization of fucoxanthin. Under optimized ultrasound-assisted conditions, the DES afforded 7.59 mg/g fucoxanthin. Untargeted metabolomics showed that the DES extract was enriched in endogenous phenolic antioxidants and contained fewer oxidation-related byproducts, while FT-IR, ¹H NMR, and DFT analyses revealed a hydrogen-bonded supramolecular network that stabilized fucoxanthin through hydrogen bonding and dispersion interactions. Accordingly, the DES reduced the photodegradation rate constant from 0.74 to 0.065 h^-1 and extended the half-life from 0.94 to 10.64 h. The DES also exhibited cold-chain stability over 40 days and reusability over 10 cycles, supporting the Thy-MeSA DES as a promising green medium for extracting and stabilizing oxidation-sensitive marine carotenoids.