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Title: Thearubigins of black tea : manufacturing-based studies
Author: Temple, Catherine Mary
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1999
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Thearubigins are polyphenolic oligmers which contribute to the quality of black tea: it is necessary to learn more of their origin and structure in order to understand their function, and to utilise opportunities to influence their development during processing to meet market demand. Tea samples were manufactured under controlled conditions, by methods parallel to commercial production in Malawi. Leaf handling, withering, fermentation and drying were manipulated. Conditions selected could be used in current commercial tea factories with only minor modifications. Non-volatile water-soluble components of black tea were analysed in an attempt to identify the critical points in the process. Solvent partition, adsorption chromatography or caffeine precipitation followed by size..exclusion HPLC were used to further separate the thearubigins and estimate molecular mass. Reverse-phase HPLC was also used; both methods were monitored by UV-VIS spectroscopy. Eluate was collected and portions challenged with chemical probes to identify functional groups within the oligmers. Theafulvin was shown to be heterogeneous in both chemical composition and mass. Prolonged fennentation in the presence of air promoted the development of theafulvin, caffeine-precipitable thearubigin, and hump unresolved by reverse-phase HPLC. This is the first evidence that theafulvin is a product of fermentation rather than a plant artefact. Leaf handling and fermentation conditions have a greater impact on liquor colour and perceived quality than withering or well-controlled drying. Modified dryer operating conditions preserved product composition and quality. Opportunities to manipulate product composition to meet market demand were identified.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Tea quality Food