Polyphenole in schwarzem Tee (Camellia sinensis)

Up to today, there are wide gaps in knowledge concerning the composition of black tea. This is, however, not due to a lack of scientific interest but rather the result of the high complexity of its constituents, in particular of the thearubigins (TRs), which bring conventional analytical tools to their limits. The term thearubigins refers to a group of compounds, which are formed during black tea manufacture through an enzymatically catalysed oxidation of flavanols and possess similar chemical, sensorial and chromatographic properties. This thesis deals with the investigation of processes during tea production, the evaluation and optimisation of different methods for the fractionation of thearubigins, and the examination of storage properties of a black tea extract. In the first part of this work model fermentations using a polyphenol-free tea-leaf-powder with active endogenous enzymes were conducted. By variation of the experimental conditions it was possible to select which of the relevant enzymes (polyphenol oxidase, PPO and/or peroxidase, POD) was active during the model oxidations. Different combinations of flavanols were used as substrates. Thus, the impact of each enzyme as well as the behaviour of the flavanols could be analysed in the course of the experiments. As a result the formation of numerous characteristic black tea constituents with different structural backbones (di- and trihydroxylated benzotropolones and -derivates, 2',2'-bisflavanols and various dehydrodicatechins) was observed. Through data obtained by HPLC-DAD-ESI-MSn several fragmentation reactions for oxidation products, such as theaflavate B, theacitrin and epitheaflagallin-3-gallate, were suggested. The results confirm the B ring to be the most reactive part of flavanols, followed by the galloyl moiety. Via qualitative and quantitative measurements of educts and products it was shown that PPO und POD catalyse the same reactions but have clearly different preferences. Despite the simplified reaction conditions the processes remained complex and led to a wide range of low-concentrated compounds. In an additional approach an oxidation system employing horseradish-POD was established and a non-enzymatic matrix effect of tea leaves was reported for the first time. The second part takes a look at three different methods for the fractionation and isolation of thearubigins (Roberts'-fractionation, precipitation with caffeine, and separation by high-speed countercurrent chromatography, HSCCC, after column chromatography with XAD-7). Based on the results the procedure using HSCCC was selected for further optimisation and the feasibility of its transfer to other techniques, namely high-performance CCC and spiral-coil CCC, was demonstrated in order to reduce the separation time or to work in a larger scale. By means of a TR-enriched solution, stability tests were carried-out in the final part of the thesis. Subject to possible differences in the matrix it was observed that the adjustment of an acidic pH value as well as continuous cooling seem to be key to maintain long storage stability.