COSMO-SAC-supported evaluation of natural deep eutectic solvents for the extraction of tea polyphenols and process optimization

To reduce the environmental pollution caused by organic solvents and improve the extraction efficiency, a range of natural deep eutectic solvents (NADESs) was explored for the extraction of green tea polyphenols (TPs). The use of the NADESs, especially ChCl/EG (Choline chloride/Ethylene glycol, molar ratio 1:2), can increase extraction efficiency when comparing with the traditional solvents. Then response surface methodology (RSM) was used for the optimization of TPs extraction with ChCl/EG. The perfect regression prediction model was generated and the highest TPs extraction yield of 20.12% was achieved, highlighting the potential of NADES for TPs extraction. Meanwhile, the applicability of COSMO-SAC (Conductor-like screening model for segment activity coefficient) for evaluation of TPs extractability in different solvents was investigated. Epigallocatechin gallate (EGCG) was employed as the TPs model solute. Geometry optimization and energy optimization of EGCG and these solvents were performed via COSMO-SAC. The extraction performance of the solvents was interpreted by the analysis of activity coefficient at infinite dilution (γ∞). The result showed that the higher the extraction yield, the lower the lnγ∞. The σ-profile and the interaction energy (EINT) were generated to analyse the molecular interaction between solvent and solute. It was demonstrated that the combination of a strong hydrogen bond acceptor (HBA) - ChCl, with a relatively weaker hydrogen bond donor (HBD) - EG, resulted in a NADES (ChCl/EG) with a stronger affinity to TPs. This work provided both experimental and intermolecular insight to help choose effective solvent for bioactive components extraction in further research.