Abstract

Natural deep eutectic solvents (NADES) can integrate extraction, preservation and formulation of bioactive food constituents within a single liquid phase. Building on prior work identifying lactic acid-glucose NADES (LA:G, 5:1 molar ratio) as an efficient solvent for recovering hydroxytyrosol (HT) from olive leaves, this study tested whether LA:G can also act as a stabilization medium and characterized the physicochemical basis for this dual-function through density, heat capacity, water content, water activity, and temperature-dependent viscosity. Ultrasound-assisted extraction at 40 degrees C and a 1:7 solid-to-solvent ratio was rapid, reaching C-HT approximate to 70 ppm within 30 min and an apparent equilibrium of approximate to 75 ppm (0.525 mg HT per g dry leaf, mass basis) between 6 and 24 h; extraction kinetics were better described by Peleg's model (R-2 = 0.984) than by an apparent first-order model (R-2 = 0.61). COSMO-RS analysis, including activity coefficients at infinite dilution, indicated a strongly favorable HT-LA:G interaction (ln gamma = - 1.515) relative to water (ln gamma = 2.632), corresponding to an activity coefficient ratio of similar to 63, reflecting a strong relative thermodynamic preference of HT for the LA:G phase. The extract also contained a broader antioxidant phenolic fraction (312 mg GAE L-1; ORAC, 10,022 & micro;mol TE L-1). Despite retaining a measurable water content (4.1%), LA:G exhibited low water activity (a(w), 0.55-0.62), indicating reduced thermodynamic water availability relative to bulk water. Over 70 days of storage, LA:G retained substantially more HT in relative terms than a water-rich reference system (70% versus 14% retention at day 10; 17% versus approximate to 0% at day 70), particularly under refrigeration and light protection, although neither system achieved long-term chemical stability. These results support LA:G as a potential functional liquid matrix integrating extraction and partial stabilization of HT-rich olive leaf extracts, in addition to its role as a green extraction solvent, for the agri-food industry.