Abstract: The contents of total phenolics (TPC) and total flavonoids (TFC) and antioxidant activities (1,1-diphenyl-2- picrylhydrazyl (DPPH) radical scavenging activity, reducing power and total antioxidant capacity) in different solvent extracts from Cyclocarya paliurus leaves (CPL) obtained with water, 70% ethanol, ethyl acetate and n-hexane were determined by the 96-well plate method. The correlation between phenolics contents and antioxidant activities was investigated and the main bioactive constituents were identified by using ultra performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC-QTOF-MS/MS). There were significant differences in the contents of total phenolics and total flavonoids and antioxidant activities among different extracts. The 70% ethanol extract showed the highest contents of total phenolics (219.01 mg GAE/g) and total flavonoids (7.23 mg CE/g), and the strongest DPPH radical scavenging activity (35.46 mg TE/g) and reducing power (1.89 mmol FeSO4/g). Each bioactive component demonstrated positive correlations with DPPH radical scavenging ability and reducing power and negative correlations with total antioxidant capacity, indicating that polyphenols mainly account for the antioxidant activities of CPL extracts. The 70% ethanol extract was analyzed by UPLC-QTOF-MS/MS, and a total of 22 compounds, including 2 organic acids, 4 phenolic acids, 5 flavonoids, 8 triterpenoid saponins and 3 esters, were identified, among which, phenolic acids and flavonoids were the major antioxidant constituents, while organic acids, triterpenoid saponins and esters might be potential antioxidant components.

Key words: Cyclocarya paliurus leaves, antioxidant activity, UPLC-Q-TOF-MS/MS, bioactive component