Fenchol- and alpha-terpineol-based eutectic solvents: antimicrobial activities and bixin extraction from annatto mixture

This study explores the development and characterization of fourteen eutectic solvents (ES) derived from natural terpenes (fenchol and α-terpineol) and fatty acids or alcohols. These ES were characterized in terms of their thermophysical (density and viscosity), thermochemical (melting behavior via DSC), and hygroscopic properties, as well as their potential antifungal activity against Fusarium graminearum and Fusarium oxysporum. Solid–liquid equilibrium diagrams confirmed the formation of eutectic mixtures with significant melting point depression, mainly due to hydrogen bond formation. The ES displayed low viscosity ranges (19.00–43.30 mPa s at 298 K) and tunable density and water absorption behavior, influenced by molecular structure and component ratios. The water content was very low, showing a range of 1.145–2.821 mg g−1 of water for the dried ES and 22.936–62.409 mg g−1 for water-saturated ES. Notably, several ES demonstrated potent antifungal effects at low concentrations (100–600 mg L−1), especially those based on short- and medium-chain fatty acids or alcohols, achieving complete growth inhibition of target fungi. Moreover, the ES were evaluated as extraction media for bixin from annatto seeds, with certain combinations outperforming conventional solvents in both yield and efficiency, reaching values as high as 1106 μg g−1 and an extraction efficiency (EE%) of 155.4 % for the Fen:C10OH-based ES. These findings suggest that terpene-based ES are promising sustainable alternatives for agrochemical applications and natural product extraction.