Ultrasonic-Assisted Deep Eutectic Solvent Extraction of Polyphenols From Tea Parts: A Green Assessment

Deep eutectic solvents (DESs) have emerged as green alternatives to conventional solvents for extracting bioactive compounds from plants. This study evaluated nine choline chloride–based DESs for recovering antioxidant polyphenols from four parts of the tea plant (Camellia sinensis): seed, bud, leaf, and flower. Total phenolic content, antioxidant activity, and individual polyphenolic profiles were determined, and the greenness of the sample preparation was assessed using AGREEprep. The highest total phenolic content (53.28 mg GAE/g) and antioxidant activity (141.17 mg TE/g) were obtained from leaves using ChCl:formic acid, outperforming ethanol and methanol. Leaves also exhibited the highest total quantified polyphenolic content (up to 95,813 mg/kg DW, corresponding to the sum of the quantified polyphenols), with epicatechin gallate and gallocatechin + epigallocatechin being the major contributors. Flowers and buds showed notable polyphenolic diversity, while seeds contained the lowest levels. Statistical analysis confirmed clear clustering patterns according to plant part and solvent type. AGREEprep evaluation yielded scores up to 0.54, highlighting the environmental benefits of DES-based extraction. We demonstrated that tea leaves were the richest source of bioactive polyphenols, and selected DESs, particularly formic acid–based and ethylene glycol–based, exhibited superior efficiency and sustainability compared to conventional solvents. These findings support the wider adoption of DESs for green, high-yield extraction of pharmacologically important compounds from tea and other medicinal plants.