Recovery of lipids and carotenoids from Dunaliella salina microalgae using deep eutectic solvents

Microalgae are natural sources of bioactive compounds used for numerous applications such as pharmaceutical, nutraceutical, cosmetic, and recently in the production of biofuels. Achieving sustainability in some biotechnological processes still requires overcoming important challenges including the fatty acid biomass extraction processes. Methanol and chloroform are generally used in the traditional extraction processes, which are toxic and present environmental risks. Thus, studies involving environmentally sustainable solvents which are less aggressive to health are necessary. In this context, deep eutectic solvents (DESs) have shown attractive characteristics. DESs stand out as adjuvants in cell disruption and biomolecule extraction stages, working as non-toxic, non-volatile, and renewable agents. This work aimed to evaluate the effect of different DESs (pure and aqueous based on choline chloride) on extracting lipids and carotenoids from Dunaliella salina. The best total lipid recovery was 67.41 % ± 6.07 achieved using a DES synthetized with choline chloride and urea (Ch-U treatment) from dry biomass by two-step extraction. On the other hand, a significant migration to the DES phase (pre-treatment) was observed for carotenoids, and consequently lower recovery values. Thus, the one-pot method was evaluated to solve this problem and reduce the process steps, and 84.06 ± 1.22 % of carotenoids were recovered from wet biomass with Ch-U treatment and ethyl acetate and ethanol (EAE) solvent. It was also observed that the treatment performed with choline chloride and oxalic acid (Ch-Ox treatment) presented one of the highest reductions in carbohydrate content among the evaluated treatments, and the most in protein content of the microalgal biomass. Finally, the strategies tested herein were validated by comparing the results with traditional methodologies (ultrasonic and ball mill). It was generally found that DESs enhanced the solvent permeability in the microalgae cell wall and the efficiency and sustainability of the extractive process can be increased depending on the chosen strategy.