Tuning bio-derived solvents for the rapid solubilization of astaxanthin-rich extracts from non-conventional bacterium Paracoccus carotinifaciens

Abstract

Astaxanthin (AXT) is a ketocarotenoid widely used in food, feed, and pharmaceutical industries. Its biological sourcing is preferred over chemical methods due to higher physiological and commercial value. Paracoccus carotinifaciens, an aerobic marine Gram-negative bacterium, is known for producing a carotenoid mixture with AXT as the main component. This study explores the use of bio-based solvents, both pure and mixed, for extracting AXT-rich extracts (ARE). Using COSMO-SAC, a quantum chemistry-based thermodynamic model, we assessed the AXT-solvent affinity. The ethyl acetate: acetic acid mixture (EtOAc:AA) gave the best results, with 1.41 mg/mL of ARE. The solvent selection process was evaluated through the Eco Scale to compare with conventional methods. Next, optimization of extraction conditions resulted in 3.28 mg/mL of ARE at 78 °C, 10 min, and a solid-to-liquid ratio of 0.5 g/mL. Ultrasound-assisted extraction (UAE) was employed to tuning the mass-transfer process, leading to an increase of ARE (18.9 %) in reduced processing time. Concerning the stability of ARE in the EtOAc:AA mixture, the half-life (t1/2) reached 18 and 26 days under the light and dark conditions, respectively at 25 °C. In both light and dark conditions, positive enthalpy (ΔH) values revealed an endothermic process and both entropy (ΔS) and Gibbs free energy (ΔG) values suggest that the degradation of ARE is less disordered and non-spontaneous process. The solvent mixture was effectively reused for three cycles under optimally tuned conditions without a significant decline of ARE extraction efficiency.