Valorization of tea (Camellia sinensis) waste: Extraction of bioactive compounds using ionic liquids and evaluation of their stability, efficiency, and volatile profiles during the process

This study explored 50 % 1-butyl-3-methylimidazolium chloride (BMIMCL) and 50 % 1-ethyl-3-methylimidazolium chloride (EMIMCL) as alternative solvents for extracting bioactives from tea waste (TW) of Camellia sinensis. As both release and degradation of catechins occur during extraction, the stability of the compounds was assessed under relevant time-temperature conditions to determine its influence on extraction. Ionic liquids (ILs) preserved catechins better than other solvents. Epigallocatechin gallate (EGCG) degradation in water was six times higher than in 50 %BMIMCL at high temperatures, while Epicatechin (EC) degradation remained under 15 %. At 70 °C and a 1:10 solute-to-solvent ratio, ILs achieved the highest EC yield, with 50 %BMIMCL yielding over 15 mg per gram of TW, whereas ethanol and water extracted none. Scanning Electron Microscopy (SEM) revealed TW structural changes supporting enhanced extraction. Additionally, volatile organic compounds (VOCs), including indicator compounds, were tracked by PTR-TOF MS (Proton Transfer Reaction - Time of Flight Mass Spectrometry) as potential real-time extraction markers.