Optimisation of sulfate polysaccharide extraction from Ulva lactuca using natural deep eutectic solvent with ultrasound assistance

Background: Ulva lactuca, or sea lettuce, is a green macroalgae found in the Indonesian Sea, containing the active component Ulvan sulfated polysaccharide. Objective: This study aims to investigate the impact of extraction-free variables on ulvan yield and its corresponding metabolomic profile. Methods: Ulvan was extracted using three choline chloride-based NADES (KKG, KKL, KKT) with ultrasonic waves, optimising variables such as temperature, solution-to-solid ratio, and power. Total polysaccharides were measured using the phenol-sulfuric acid method, while total sulfates were measured by BaCl2 absorption turbidimetry at 490 nm and 420 nm. Ulvan metabolomic profiles were assessed via FTIR, XRD, and LC-HRMS. Results: The independent variables consisted of 3 factors and 3 levels, resulting in 51 test points with optimum parameters: temperature at 78.27°C, L/P ratio at 39.62, and ultrasonic power at 139.23 watts. KKG achieved the highest yield at 11.7% ± 0.706, with sulphate levels ranging from 6.37% to 10.4% across all NADES. Extraction results were influenced by both single and combined independent variables. FTIR metabolomics revealed -CH, -S=O, -C=O, and -SO₄ groups, while LC-HRMS identified Rhamnosa 3-sulphate and DI-Xylosa compounds. UHD contains the Xylose-Rhamnosa 3-sulphate chain, part of Ulvanobiosis U3s. Conclusion: Choline chloride-based NADES, with ultrasound assistance, shows potential as a method for isolating active compounds from marine biota.