Viola S. Y. Lee

Massive Accumulation of Gallic Acid and Unique Occurrence of Myricetin, Quercetin, and Kaempferol in Preparing Old Oolong Tea

Old oolong tea, tasting superior and empirically considered beneficial for human health, is prepared by long-term storage accompanied with periodic drying for refinement. Analyzing infusions of three old and one newly prepared oolong teas showed that significant lower (-)-epigallocatechin gallate (EGCG) but higher gallic acid contents were detected in the old teas compared to the new one. The possibility of releasing gallic acid from EGCG in old tea preparation was supported by an in vitro observation of gallic acid degraded from EGCG under heating conditions mimicking the drying process. Moreover, three minor flavonols, myricetin, quercetin, and kaempferol, that were undetectable in the new tea occurred in all of the three old teas. Converting the new oolong tea into an old one by periodic drying revealed the same characteristic observation, i.e., massive accumulation of gallic acid presumably released from EGCG and unique occurrence of flavonols putatively decomposed from flavonol glycosides.

Study of the release of gallic acid from (–)‐epigallocatechin gallate in old oolong tea by mass spectrometry

Liquid chromatography combined with multiple-stage mass spectrometry (LC/MS(n)) was used to study the pathway of the release of gallic acid (GA) from epigallocatechin gallate (EGCG) in infusion of old oolong tea. The possibility of releasing GA from EGCG in old tea preparations was supported by an in vitro observation of GA degraded from EGCG under heating conditions mimicking the drying process. Negative electrospray ionization with the data-dependent mode of MS(n) was used to study the formation pathway of GA in old oolong tea. The MS(n) data show that GA was released from the dimer of EGCG, not directly degraded from EGCG.

Teaghrelins, Unique Acylated Flavonoid Tetraglycosides in Chin-Shin Oolong Tea, Are Putative Oral Agonists of the Ghrelin Receptor

Chin-shin oolong tea, a popular tea in Taiwan, was empirically perceived to induce hunger and accelerate gastric emptying in a manner similar to the physiological effects of ghrelin, an endogenous acylated peptide known as the hunger hormone. Two unique acylated flavonoid tetraglycosides previously identified in Chin-shin oolong tea were demonstrated to induce hunger of rats in a food intake assay and, thus, named teaghrelin-1 and teaghrelin-2. Similar to GHRP-6, a synthetic analogue of ghrelin, teaghrelin-1 stimulated growth hormone secretion of rat primary anterior pituitary cells in a dose-dependent manner, and the stimulation was inhibited by [D-Arg(1),D-Phe(5),D-Trp(7,9),Leu(11)]-substance P, an antagonist of the ghrelin receptor. While teaghrelin-2 remained unmodified, a meta-O-methylated metabolite of teaghrelin-1 was detected in bile of rats after intravenous injection. Presumably, teaghrelins are promising oral agonists of the ghrelin receptor.

Gallic Acid in Old Oolong Tea

Due to the semi-fermentation process, the taste and color of oolong tea are between those of green and black teas. The notation ‘ old oolong tea ’ is used if the oolong tea has been stored for more than five years and refined annually by a drying process in an oven at various temperatures. After such long storage conditions, and undergoing chemical changes induced by the repeated drying processes, old oolong teas are considered to have a better taste and greater beneficial effects on human health than normal oolong teas (i.e. those not stored nor subjected to annual processing). Infusions of new and old oolong teas have been analyzed by liquid chromatography coupled to ultraviolet visible detection and tandem mass spectrometry. These studies show that there is less epigallocatechin gallate and more gallic acid in old oolong tea compared to newer oolong tea. Studies on the release of gallic acid from epigallocatechin gallate have been characterized by analyzing heated epigallocatechin gallate solutions via liquid chromatography coupled to multiple-stage tandem mass spectrometry. The results show that the gallic acid in old oolong tea is not only directly degraded from epigallocatechin gallate but also released from the dimer of epigallocatechin gallate.