Identification of trimeric and tetrameric flavan-3-ol derivatives in the SII black tea thearubigin fraction of black tea using ESI-tandem and MALDI-TOF mass spectrometry

• Black tea is chemically a complex mixture comprising an estimated 30 000 individual compounds with thearubigins as their main components.
• A series of complementary mass spectrometry were employed for structural elucidation of thearubigins constituents exceeding 1000 Da.
• Results revealed for the first time the presence of oligomeric components formed from oxidative coupling between flavan-3-ols and their dimers
• This study comprised a key step forward for unraveling the mystery of black tea thearubigins.

Direct infusion MSn and MALDI-TOF-mass spectrometry were applied for characterizing thearubigins isolated from black tea. Components of the so-called SII fraction of thearubigins obtained through caffeine precipitation were studied exclusively. New components with molecular weights higher than 1000 Da were analyzed and structurally characterized. The data generated revealed clearly the presence of different trimeric and tetrameric flavan-3-ols formed through oxidative coupling between flavan-3-ols and their dimers, most notably theaflavin and theasinensin within the black tea thearubigins. Our data are fully consistent with the oxidative cascade hypothesis of thearubigin formation and provide for the first time experimental evidence on oxidative oligomerization of flavan-3-ols and their dimers to form oligomeric flavan-3-ols.