Extraction for profiling free and bound phenolic compounds in tea seed oil by deep eutectic solvents

Bound phenolic compounds have rarely been reported in vegetable oils and this may be due to little research about the extraction. Deep eutectic solvents (DESs), recently applied in the extraction of phenolic compounds as alternatives to organic solvents, were adopted in the extraction of free and bound phenolic compounds from tea seed oil in this work. First, the phenolic compounds were analyzed by ultra-high-performance liquid chromatography with quadrupole-time-of-flight and triple-quadrupole tandem mass spectrometry (UHPLC-Q-TOF-MS/MS) for characterization and UHPLC-QqQ-MS/MS for quantification and 25 phenolic compounds were found to exist in both free and bound forms. Then, DESs were screened for extraction of free and bound phenolic compounds from tea seed oil as the pretreatment for analysis and the results showed that hydrogen bond donors (HBDs) and temperature significantly affected the extraction efficiency of DESs. Finally, free phenolic compounds (83.91 µg/g) and bound phenolic compounds (25.71 µg/g), extracted by the DES with glycerol as HBD at 50 °C, were 51.0% and 93.2% higher than those extracted by methanol/water (60%, v/v), respectively. This work not only advanced the basic data of phenolic compounds in tea seed oil but also explored an efficient extraction method for scientific analysis of free and bound phenolic compounds.