No abstract

Samples of tea (Quingmao, steamed, black and Pu'er) produced in Yunnan Province, People's Republic of China, from the locally characteristic large-leaved Camellia sinensis, have been brewed and the brews analysed for their contents of flavonol glycosides, flavan-3-01s and their oxidation products. Several samples of Pu'er tea manufactured in the 192Os, 1930s and 1940s were also examined. The brews prepared from Quingmao tea and steamed green tea leaf were very similar containing primarily flavan-3-01s accompanied by flavonol glycosides, theogallin and gallic acid. The profile of flavanols was unusual, being dominated by (-)-epicatechingallate (rather than ( -)-epigallocatechingallate) and by an unusually large (+)-catechin content. The brew of the equivalent black tea retained significant amounts of residual flavanols (particularly (-)-epicatechingallate and ( +)-catechin), and contained significant amounts of thearubigins, theaflavic acids and theaflavins (including the less common analogues probably derived from the oxidation of ( + kcatechin). The brews prepared from the Pu'er teas were distinguishable from the black tea brew by the absence of theaflavins and theaflavic acids, and by much smaller residues of flavanols and flavonol glycosides. The contents of thearubigins varied considerably whereas those of gallic acid were similar.

A simutaneous distillation extraction (SDE) combined GC method was constructed for determination of volatile flavor components in Pu-erh tea samples. Dichloromethane and ethyl decylate was employed as organic phase in SDE and internal standard in determination, respectively. Weakly polar DB-5 column was used to separate the volatile flavor components in GC, 10 of the components were quantitatively analyzed, and further confirmed by GC-MS. The recovery covered from 66.4%–109%, and repeatability expressed as RSD was in range of 1.44%–12.6%. SDE was most suitable for the extraction of the anlytes by comparing with steam distillation-liquid/liquid extraction and Soxhlet extraction. Commercially available Pu-erh tea samples, including Pu-erh raw tea and ripe tea, were analyzed by the constructed method. the high-volatile components, such as benzyl alcohol, linalool oxide, and linalool, were greatly rich in Pu-erh raw teas, while the contents of 1,2,3-Trimethoxylbenzene and 1,2,4-Trimethoxylbenzene were much high in Pu-erh ripe teas.

No abstract

The possibility of using GC-ECD to determine glucosidically bound aroma precursors was investigated. Five b-D-glucopyranosides were derivatized with N-methylbis(trifluoroacetamide) (MBTFA) and then determined by GC-ECD, which showed these mono-glycosides (glucosides) could be separated and identified by GC. Repeatability, sensitivity and stability were tested, relative standard deviation (RSD) was in the range of 0.55-5.9%, the limit of detection (LOD) was lower than 10 -3 lg mL -1 , and the standard mixture was stable within 3 days (stored at 4°C, peak areas RSD \ 3%). Application of the developed derivatization and determination method to the fresh tea leaves showed that the glucosides could be accurately quantified (using phenyl b-D-glucopyranoside as internal standard). Because of its high sensitivity, the developed method was suitable for the determination of glucosides in fresh tea leaves.