Potential of microalgae biomass as carotenoids source using natural deep eutectic solvents

The potential of microalgae Chlorella vulgaris as a carotenoid source was explored using a novel class of solvents known as Natural Hydrophobic Deep Eutectic Solvents (NaHDESs). Seven lowviscosity NaHDESs, composed exclusively of fatty acids that act as hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) simultaneously, were characterized and assessed for their ability to extract carotenoids from Chlorella vulgaris. Through screening, nonanoic/dodecanoic acid (3:1) was identified as the most effective NaHDES. Its HBA:HBD molar ratio was optimized using Box-Behnken Design. Additionally, the optimization process considered solvent:sample ratio and extraction time, evaluating their impact on carotenoid recovery, specifically focusing on lutein, zeaxanthin, and β-carotene, and antioxidant activity, through ABTS, and DPPH assays. Under the optimized extraction conditions, the recovered amounts of total carotenoids, lutein, zeaxanthin, and β-carotene were 2.00 ± 0.31, 1.42 ± 0.01, 0.16 ± 0.01, 0.70 ± 0.01 mg/mL of extract, respectively. The extract also demonstrated significant antioxidant capability, with an inhibition level of 9.13 ± 0.18 % per mL of extract. These findings highlight the superior performance of nonanoic acid/dodecanoic acid (1:1) over acetone and underscore the potential of NaHDESs as a promising alternative to traditional solvents for extracting bioactive compounds from microalgae such as Chlorella vulgaris.