Rapid screening and identification of antioxidants in aqueous extracts of Houttuynia cordata using LC–ESI–MS coupled with DPPH assay

Houttuynia cordata Thunb. has been used traditionally as immune stimulant and anticancer agent. An aqueous extract of H. cordata tea showed high radical scavenging activity determined by off-line DPPH assays. Then, it was screened for its antioxidant components via an on-line DPPH radical scavenging technique coupled with a liquid chromatography–electrospray ionization mass spectrometer (LC–ESI–MS). Based on their mass spectra and fragmentation patterns; the antioxidant compounds were identified as quinic acid derivative, caffeic acid derivatives, procyanidin B, neo-chlorogenic acid, catechin, chlorogenic acid, crypto-chlorogenic acid and quercetin hexoside. LC–MS/MS in multiple reactions monitoring (MRM) mode was used to quantify these antioxidant compounds. Chlorogenic acid was found to be a major component in H. cordata tea.