Isolation and identification of compounds from the ethanolic extract of flowers of the tea (Camellia sinensis) plant and their contribution to the antioxidant capacity

While beneficial health properties of tea leaves have been extensively studied, less attention has been given to that of flowers of the tea (Camellia sinensis) plant. In this work, the ethanolic extract and its ethyl acetate-soluble fraction (EEA) from the tea flowers were found to possess the potent antioxidant activity using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assay. The compounds present in EEA had comparatively strong DPPH scavenging activity and strongly contributed to the antioxidant activity of the tea flowers. From EEA, besides eight catechins, five flavonol glycosides were isolated and their structures were elucidated on the basis of mass spectrometry and nuclear magnetic resonance spectroscopy as myricetin 3-O-β-d-galactopyranoside, quercetin 3-O-β-d-galactopyranoside, kaempferol 3-O-β-d-galactopyranoside, kaempferol 3-O-β-d-glucopyranoside, and kaempferol 3-O-[α-l-rhamnopyranosyl-(1-6)-β-d-glucopyranoside]. In addition, epigallocatechin gallate and epicatechin gallate were found as the major active components responsible for the antioxidant activity of tea flowers through the use of a combination of preparative liquid chromatography separation and DPPH assay.