Green extraction of pigment from astaxanthin-producing algae using natural deep eutectic solvents

The high-value carotenoid astaxanthin is a powerful antioxidant with various purported health benefits. The alga Haematococcus lacustris (formerly pluvialis) represents the main natural (farmed) source of astaxanthin. Additionally, Chlamydomonas reinhardtii has been engineered to produce ketocarotenoids including canthaxanthin, astaxanthin, and intermediates that accumulate with its native carotenoids and chlorophylls. Carotenoid extraction from biomass conventionally employs organic solvents such as acetone and ethanol. Here, the use of natural deep eutectic solvents (NADES), composed of food-grade components, was explored as green alternative for the extraction of total pigments, including astaxanthin, from engineered C. reinhardtii and wild-type H. lacustris. Hydrophobic menthol-based NADES extracted up to 2.0 mg of astaxanthin g⁻¹ of dry algal biomass from engineered C. reinhardtii and 13.4 mg g⁻¹ of wildtype H. lacustris, respectively, in single two-hour extractions, giving an extraction efficiency of 79 % and 204 % compared to organic-solvents, respectively. The extractions were carried out at room temperature without necessitating additional energy inputs like heating or sonication and without any pretreatments. The food-grade nature of NADES suggests the feasibility of utilizing the extracted materials in supplements and health applications, offering a cost-effective and sustainable means of converting waste biomass into valuable products.