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.