Compositional and biochemical activity evaluation of highly polymerized tea pigments in black tea based on natural deep eutectic solvent extraction

Highly polymeric tea pigments (HPTPs) in black tea have not been comprehensively analyzed because of the complex composition of their structural components. 14 natural deep eutectic solvents (NADESs) were evaluated for extracting HPTPs from black tea, and choline chloride-urea (ChCl-UA) was selected as the best candidate. The HPTPs were separated from the NADES using a dialysis membrane. Microstructural analysis was conducted by XRD, SEM, and AFM, combined with thermal property analysis using TG-DSC and Py-GC-MS determination of biochemical components, and structural analysis through UV-visible, FT-IR, NMR, and SERS spectroscopies. The antioxidant activity analyzed using ABTS, DPPH, and FRAP assays. The results revealed that the extract obtained using the ChCl-UA has a higher tea pigment content, greater polymerization degree, and simpler impurities. The extraction of HPTPs using a NADES and the analysis of the chemical composition and structural characteristics of the extract are helpful for understanding the macromolecular pigments in tea.