- no.50, pp.475-480, 2008-09-01
Oolong tea is a semi-fermented tea, which has been manufactured from leaves of Camellia sinensis (L) O. Kuntze, same as non-fermented Japanese or Chinese green teas. Major components of fresh tea leaves are caffeine and catechins such as epigallocatechin-3-O-gallete (EGCG). During the fermentation process, polyphenol oxidase (PPO) in tea leaves oxidizes the catechins into theasinensin and oolongtheanin. In addition, oolonghomobisflavans are known as condensation products of catechins by heat treatment. The aim of this study is to quantify these minor polymerized polyphenols by LC-MS/MS, and address their biological activities. Quantification of polyphenols by LC-MS/MS Theasinensin (TSN), oolongtheanin gallate (OTNG), and oolonghomobisflavan (OHBF) were synthesized from EGCG. Two new trimers and tetramers of oolonghomobisflavan were synthesized along the previous synthesis method of OHBF, and then their structures were determined by MS and NMR spectroscopy. Quantification of these compounds was performed by LC-MS/MS in the mode of multiple reaction monitoring (MRM). Compounds other than TSN-A were of small quantities in oolong tea leaves. Quantification of polymerized polyphenols was not performed with HPLC UV monitoring, but by LC-MS/MS method. Nine kinds of oolong teas in different fermentation levels were extracted and analyzed. The very small amount of trimers and tetramers of OHBF were included in "Black oolong tea", therefore, it was necessary to make concentrated solutions of these by column separation, and quantified the real amount by analyzing them. Biological activities of polymerized polyphenols Pancreatic lipase inhibitory activity of oolong tea polymerized polyphenols (OTPP) and some catechin dimmers have been already reported. In this study, new trimers and tetramers also exhibited strong inhibitory activity. Besides OTPP, the polymerized polyphenols, TSN, OTNG, and OHBF also have α-glucosidase inhibitory activity. These results suggest that oolong tea prevents the elevations of triglyceride in blood from meal fat, as well as inhibit the absorption of sugars derived from carbohydrates.