Tailored natural deep eutectic solvents for selective extraction and long-term stabilization of Bixin from annatto seeds

This study investigated the use of Natural Deep Eutectic Solvents (NADES) for the selective extraction of bixin from Bixa orellana L. (annatto) seeds. For the first time, Hansen Solubility Parameters (HSPs) were systematically applied to predict bixin-solvent affinity, identifying a decanoic acid-menthol system at a 2:1 M ratio (DA:Men 2:1) as the optimal extraction medium mainly due to its solubility distance from bixin (R a = 2.61). Extraction kinetic experiments conducted at 50 °C with a solvent concentration of 0.1 g mL −1 revealed that the hydrophobic DA:Men 2:1 NADES achieved a bixin concentration of 2.09% ( w /w) in 30 min, while a conventional ethanol-water (1:1, v /v) solvent reached 0.0075% ( w /w) for bixin concentration under identical conditions. Response surface methodology (RSM) was employed to verify the influence of extraction temperature and solvent concentration on bixin concentration using the hydroalcoholic mixture and the DA:Men 2:1 NADES as solvents. Results of statistical analysis confirmed the greater bixin concentration in the extract with NADES than with the hydroalcoholic solvent at different extraction temperatures and seed-to-solvent ratios. The temperature was the most significant variable in the ethanol-water extraction, while the DA:Men 2:1 NADES extraction was primarily driven by the seed-to-solvent ratio, requiring only moderate thermal conditions. Chromatographic analyses of the extracts after 30 days of storage showed that the bixin concentration remained almost constant with the DA:Men 2:1 NADES, but complete bixin degradation occurred in the ethanolic extract. Furthermore, LC-MS analyses revealed that the ethanolic annatto extract comprised a wide range of phenolic and secondary compounds, and the DA:Men 2:1 NADES extract exhibited a distinctly higher bixin purity. These findings demonstrate the potential of the hydrophobic DA:Men 2:1 NADES as sustainable, high-performance solvents for the recovery of lipophilic bioactive compounds, yielding highly concentrated, pure, and stable extracts.