Enrichment, analysis, identification and mechanism of antioxidant components in Toona sinensis

The tender leaves of Toona sinensis not only taste delicious, but also have a wide range of biological activities, including strong antioxidant activity. In this study, a method based on liquid-liquid-refining extraction and bioassay-guided separation were established and developed for enrichment, analysis and identification of antioxidant components in T. sinensis. Two main antioxidants, 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PGG) and ethyl gallate (EG) with strong antioxidant capacity were responsible for the antioxidant activity of T. sinensis. The EC₅₀ of EG scavenging ABTS·⁺ and DPPH· were 22.53 ± 0.25 µM and 38.43 ± 0.66 µM, and the EC₅₀ of PGG were 13.72 ± 0.17 µM and 17.33 ± 0.21 µM. The thermodynamic parameters of various pathways indicated that single electron transfer followed by proton transfer (SET-PT) was the main antioxidant mechanism of PGG and EG. Furthermore, the results of frontier molecular orbital theory and reaction kinetics showed that PGG had low energy gap and reaction energy barrier, which was the fundamental reason why its antioxidant activity was better than EG.