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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 504165
Title Oligomerization and hydroxylation of green tea catechins by oxidative enzymes
Author(s) Verloop, J.W.
Source University. Promotor(en): Harry Gruppen, co-promotor(en): Jean-Paul Vincken. - Wageningen : Wageningen University - ISBN 9789462577770 - 146 p.
Department(s) Food Chemistry Group
VLAG
Publication type Dissertation, internally prepared
Publication year 2016
Keyword(s) green tea - oxidation - theaflavine - peroxidase - oxygenases - flavanols - phenolic compounds - catechol oxidase - mass spectrometry - maldi-tof - process control - groene thee - oxidatie - oxygenasen - flavanolen - fenolverbindingen - massaspectrometrie - procesbewaking
Categories Food Chemistry
Abstract

Black teas are known for their characteristic brown colour, bitter taste and astringent mouth feel. These sensory characteristics are mainly influenced by the phenolic oxidation products present in black tea. The oxidation of phenolics from green tea leaves during black tea manufacturing is an uncontrolled process. With the objective to make tea oxidation a more controlled process, the aim of this thesis was to understand the enzymatic oxidation reactions occurring during tea oxidation, and to enable more rapid analysis of complex mixtures of phenolics. By incubating green tea catechins with an exogenous tyrosinase, a black tea-like phenolic profile was obtained, enriched in theaflavins, which are important for quality of tea. Further oxidation of theaflavins yielded theatridimensins, in which an epicatechin is coupled to the benzotropolone ring of theaflavin. By using MS/MS on selected ions these theatridimensins were shown to occur in black tea. This MS method could also be used to distinguish isomeric procyanidins and dehydrocatechins based on MS2 fragments, as well as the different interflavanic configurations occurring in dehydrodicatechins. The dehydrocatechins were shown to occur in black tea as well. Besides these oligomerization reactions mediated by tyrosinase, oxidation of tea phenolics also comprised hydroxylation. The enzymatic activity from tea leaves responsible for this hydroxylation reaction, was found to be peroxidase. All findings were condensed into a new version of the ‘oxidative cascade hypothesis’, describing the oxidation reactions towards formation of a black tea.

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