Optimization of Antioxidant Recovery from Deep Eutectic Solvent Phase via Back-Extraction Using Taguchi Method

This study investigates the use of deep eutectic solvents (DESs) via ethyl acetate-mediated liquid–liquid extraction and the optimization of the process using the Taguchi method for the recovery of antioxidant compounds from tea industry waste. In the study, choline chloride was used as a hydrogen bond acceptor; lactic acid, glycerol, and ethanol were used as hydrogen bond donors; and different ratios of water (10–30%) were added to reduce the viscosity of the DESs. Ultrasound-assisted extraction results showed that lactic acid-based DESs provided the highest total phenolic content and antioxidant activity due to their ability to break down plant cell walls. However, in the recovery phase carried out with ethyl acetate, it was determined that ethanol-based DESs (ChCl:EtOH) were more effective in transferring antioxidants to the organic phase due to their looser molecular structure. Optimization using the Taguchi L9 orthogonal array revealed the following results: ChCl:EtOH solvent, 2:1 ethyl acetate/extract ratio, 20% water ratio, and 30-min shaking period were determined as the optimal conditions. Under these conditions, the model predicted a yield of 93.34%, and experimental validation revealed a recovery yield of 85.70 ± 1.13%. The results demonstrate that this developed green extraction method offers a sustainable alternative for converting tea waste into high value-added functional components.