title: Antioxidative activities of volatile extracts from green tea, oolong tea, and black tea.
abstract: Antioxidative activities of volatile extracts from six teas (one green tea, one oolong tea, one roasted green tea, and three black teas) were investigated using an aldehyde/carboxylic acid assay and a conjugated diene assay. The samples were tested at levels of 20, 50, 100, and 200 micrograms/mL of dichloromethane. The results obtained from the two assays were consistent. All extracts except roasted green tea exhibited dose-dependent inhibitory activity in the aldehyde/carboxylic acid assay. A volatile extract from green tea exhibited the most potent activity in both assays among the six extracts. It inhibited hexanal oxidation by almost 100% over 40 days at the level of 200 micrograms/mL. The extract from oolong tea inhibited hexanal oxidation by 50% in 15 days. In the case of the extract from roasted green tea, the lowest antioxidative activity was obtained at the level of 200 micrograms/mL, suggesting that the extract from roasted green tea contained some pro-oxidants. The extracts from the three black teas showed slight anti- or proactivities in both assays. The major volatile constituents of green tea and roasted green tea extracts, which exhibited significant antioxidative activities, were analyzed using gas chromatography-mass spectrometry. The major volatile chemicals with possible antioxidative activity identified were alkyl compounds with double bond(s), such as 3,7-dimethyl-1,6-octadien-3-ol (8.04 mg/kg), in the extract from green tea and heterocyclic compounds, such as furfural (7.67 mg/kg), in the extract from roasted green tea. Benzyl alcohol, which was proved to be an antioxidant, was identified both in a green tea extract (4.67 mg/kg) and in a roasted tea extract (1.35 mg/kg).
authors.affiliation: Department of Environmental Toxicology, University of California, Davis, California 95616.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Yanagimoto
authors.forename: Hirotomo
authors.initials: H
authors.lastname: Ochi
authors.forename: Kwang-Geun
authors.initials: KG
authors.lastname: Lee
authors.forename: Takayuki
authors.initials: T
authors.lastname: Shibamoto
mesh_terms: D000447:Aldehydes / Q000032:analysis / Q000737:chemistry; D000975:Antioxidants / Q000032:analysis*; D028241:Camellia sinensis / Q000737:chemistry*; D002264:Carboxylic Acids / Q000032:analysis / Q000737:chemistry; D006358:Hot Temperature; D008041:Linoleic Acids / Q000737:chemistry; D008752:Methylene Chloride; D010084:Oxidation-Reduction; D010936:Plant Extracts / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry*; D014835:Volatilization
chemical_list: D000447:Aldehydes; D000975:Antioxidants; D002264:Carboxylic Acids; D008041:Linoleic Acids; D010936:Plant Extracts; C005575:methyl linoleate; D008752:Methylene Chloride