Deep eutectic solvents for green extraction of plant essential oils: mechanisms, critical review, and future...

This review critically evaluates the mechanistic insights, technical controversies, and industrialization challenges of deep eutectic solvents (DESs) in the green extraction of plant essential oils (EOs), moving beyond the descriptive case enumeration that dominates the existing literature. First, a quantitative causal framework is established linking molecular hydrogen-bond interactions (molecular dynamics simulations, -25 to -35 kJ/mol) to macroscopic extraction kinetics (washing rate constant enhanced 2.6-14-fold) and oxygenated terpene enrichment (median increase 18-35%; maximum 3.45-fold). Second, two long-standing contradictions are resolved, namely, optimal water content (38.6% vs. 87.5%) and conflicting attributions of oxygenated terpene enrichment, through a unified DES type × matrix lignification interaction model and a temperature‑dependent hydrogen‑bond protection mechanism with falsifiable predictions. Third, widespread experimental flaws are quantified: 72.7% of studies lack proper controls, 81.8% present mechanistic claims without falsification tests, and 95.5% claim greenness without energy or CO₂ data. Key challenges (viscosity-mass transfer trade‑off, insufficient toxicological data, scale‑up difficulties, and regulatory barriers) and industrial solutions are critically assessed. This forward‑looking review guides the field from descriptive reporting to mechanistic understanding and practical application.