title: A novel black tea pigment and two new oxidation products of epigallocatechin-3-O-gallate.
abstract: During tea fermentation, oxidation-reduction dismutation of a number of quinone metabolites of tea catechins yields numerous minor products, which make it difficult to separate and purify black tea polyphenols. In this study, epigallocatechin-3-O-gallate was enzymatically oxidized and then the unstable quinone metabolites in the oxidation mixture were hydrogenated with 2-mercaptoethanol to reduce production of inseparable minor dismutation products. As a result, three new oxidation products including a new black tea pigment were isolated, and their structures were determined based on chemical and spectroscopic data. Dehydrotheasinensin AQ is a new reddish-orange pigment with a 1,2-diketone structure, and its presence in commercial black tea was confirmed. In addition, a new quinone dimer with a complex caged structure and a trimer of epigallocatechin-3-O-gallate were also isolated and their production mechanisms are proposed. The presence of this trimer suggested participation of galloyl quinones in production of minor polyphenols in black tea.
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University, Japan. t-tanaka@net.nagasaki-u.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Isao
authors.initials: I
authors.lastname: Kouno
mesh_terms: D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010860:Pigments, Biological / Q000032:analysis* / Q000737:chemistry; D011809:Quinones / Q000737:chemistry; D013662:Tea / Q000737:chemistry*
chemical_list: D010860:Pigments, Biological; D011809:Quinones; D013662:Tea; C417940:gallocatechin gallate; D002392:Catechin