Optimization of a Switchable Fatty Acid-Based NADES for Sustainable Recovery of Astaxanthin from Haematococcus pluvialis

Abstract

In this study, astaxanthin was extracted from the microalgae Haematococcus pluvlias using natural deep eutectic solvents (NADES). Seven NADES, based on fatty acids and menthol, were prepared and evaluated. NADES composed solely of fatty acids (caprylic:pelargonic acid, 1:1) was selected for further optimization. Optimization was performed using Box-Behnken design within response surface methodology, with total carotenoid content, astaxanthin content and energy consumption set as response variables. Optimal conditions were temperature of 31°C, extraction time of 45 minutes and an algae/NADES ratio of 1.5:10 (w/w). The selected NADES demonstrated comparable performance to acetone (14.10 ± 3.23 compared to 14.23 ± 6.53 mg astaxanthin/g algae). Astaxanthin was successfully recovered via polarity switching, enabling in situ precipitation of over 90% astaxanthin within 1 hour. This recovery step relied on the switchable nature of the NADES used, whose hydrophobic character can be reversibly transformed into a hydrophilic form upon application of polyetheramine, thereby facilitating astaxanthin separation from the solvent phase. This method offers a simple, scalable, and sustainable alternative for astaxanthin extraction, with potential application in the food, nutraceutical, pharmaceutical, and cosmetic formulations.