Sustainable ultrasound-assisted extraction of carotenoids from the seaweed Ulva lactuca: Performance of the green biosolvents 2-Methyltetrahydrofuran (2-methyl oxolane) and ethyl lactate and optimization using response surface methodology.

This study aimed to evaluate the efficiency of ultrasound-assisted extraction (UAE) combined with green solvents for recovering carotenoids from dehydrated Ulva lactuca. Two green solvents (ethyl lactate and 2-methyltetrahydrofuran (2-MeTHF) were compared with conventional food-grade solvents (acetone, ethyl acetate, ethanol, and hexane). UAE significantly outperformed conventional maceration in carotenoid yield, depending on the solvent and compound. Ethanol and 2-MeTHF showed the highest total carotenoid content (TCC), with 2-MeTHF demonstrating high extraction efficiency across multiple carotenoids, including (all-E)-lutein and (9Z)-fucoxanthin. Response surface methodology identified amplitude, extraction time, and solvent-to-sample ratio as key variables. Under optimal conditions (64.7 % amplitude, 10 min, 70 mL/g), the TCC reached 37.79 μg/g dw (dry weight)-3.4 times higher than the lowest tested condition. The comparative greenness assessment highlighted 2-MeTHF as a sustainable and effective alternative to petroleum-based solvents for carotenoid extraction using UAE.