Annotation of Different Dehydrocatechin Oligomers by MS/MS and Their Occurrence in Black Tea

Abstract

Dehydrocatechins (DhC's), oligomeric oxidation products of (epi)catechins, were formed in model incubations of epicatechin with mushroom tyrosinase. DhC oligomers up to tetramers were detected by reversed-phase ultrahigh-performance liquid chromatography mass spectrometry (RP-UHPLC-MS) analysis. Measurements with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) showed formation of oligomers up to at least 15 catechin subunits. Isomeric DhC's were obtained, and a method based on MS(2) fragment ratios was set up to distinguish between the different interflavanic configurations of the isomers. In the model incubation, 8 dehydrodicatechins (DhC2's) and 22 dehydrotricatechins (DhC3's) were tentatively annotated by their MS(2) signature fragments. Three different interflavanic configuration types were determined for the DhC2's. DhC2's and DhC3's were shown to occur in a black tea extract for the first time. For the DhC2's, at least two isomeric types, i.e., DhC β and DhC ε, could be annotated in black tea.

Browning of Epicatechin (EC) and Epigallocatechin (EGC) by Auto-Oxidation

“…Besides the brown δ-type DhC 2 s, several peaks with m / z 577 (Figure S1B), which possessed no absorbance in the range of 400–500 nm, were prominent in the full MS chromatograms. Based on a comparison of their CID fragmentation spectra (Figure S2) with the MS 2 -based decision tree, these colorless dimers were tentatively identified as β-type DhC 2 s. These β-type DhC 2 s also possess an A–B ring interflavanic linkage between two EC subunits. These results suggested that the auto-oxidation process may be a multistep oxidation process, similar to the oxidative cascade during the enzymatic oxidation. , The colorless β-type DhC 2 s are potential intermediates for the formation of the brown δ-type DhC 2 s.…”

Peroxidase Can Perform the Hydroxylation Step in the “Oxidative Cascade” during Oxidation of Tea Catechins

“…PPO is mainly responsible for the first oligomerization of the catechins. This involves a basic oligomerization step, resulting in either the dimers TF, TS, TC, or DhCs β AB /ε AB . , Simultaneous with these oxidation reactions, limited amounts of H 2 O 2 are formed by PPO. , For the subsequent oxidation steps, both PPO and POD can be responsible. The subsequent oxidation steps can be either another oligomerization or an intramolecular rearrangement.…”

“…This involves a basic oligomerization step, resulting in either the dimers TF, TS, TC, or DhCs β AB /ε AB . 1,11 Simultaneous with these oxidation reactions, limited amounts of H 2 O 2 are formed by PPO. 21,29 For the subsequent oxidation steps, both PPO and POD can be responsible.…”

“…The oligomerization and rearrangement levels have been extensively studied, and the substrates and products involved are largely known (Figure ). The level of oligomerization can be divided into two types of oligomerization: (i) basic oligomerization types, which can be formed from two subunits in one oxidation step: the theaflavin (TF) type, , the theasinensin (TS) type, − the theacitrin (TC) type, , and the dehydrocatechins (DhCs) β AB and ε AB types, , and (ii) tripartite oligomerization types, which require a preformed basic oligomerization between two catechin subunits serving as a scaffold onto which a third catechin is superimposed. An example of the latter is the theatridimensin (T3D) type. , Both types of oligomers can also undergo intramolecular rearrangements when oxidized, in which the interflavanic configuration is altered.…”

Stereochemistry of a Cyclic Epicatechin Trimer with C3 Symmetry Produced by Oxidative Coupling

“…However, dehydrodi‐(epi)‐catechins were produced by the enzymatic oxidative coupling of catechol‐type flavan‐3‐ols between A‐ring and B‐ring (Scheme 1). [3] Dehydrodi(epi)catechins and their related oligomers are found in not only black tea [3l] but also grape pomace, [4] cocoa, [5] and beer [6] . Dehydrodi(epi)catechins are also produced nonenzymatically by autoxidation, [7] radical oxidation, [8] photooxidation, [9] oxidation with CuCl 2 , [10] oxidation with FeSO 4 , [11] and heat treatment [12] .…”