Concurrent Accumulation of Myricetin and Gallic Acid Putatively Responsible for the Umami Taste of a Specialized Old Oolong Tea

Strong umami taste was perceived in a specialized old oolong tea reproducibly converted from a fresh oolong tea by fierce baking biannually for five years. Phenolic compounds in this umami tea and those in an initial fresh oolong tea were analyzed and compared. The results implied that the abundant catechin derivatives and flavonol glycosides were significantly reduced while three compounds were evidently accumulated after the tea conversion. These three compounds were chemically identified as gallic acid and two correlated flavonols, myricetin and quercetin. Molecular modeling suggested that myricetin and gallic acid might serve as ligand and enhancer to activate the umami receptor synergistically. Binary docking of myricetin and gallic acid induced the gate closure of the binding cavity in the umami receptor, in a manner similar to that of glutamate and its enhancer, inosine 5'- monophosphate. Regardless the induced fitness, the detailed molecular interactions between these two sets of binary components and the receptor were drastically different. In this binary docking modeling for umami taste, myricetin could not be equivalently replaced with any of the major tea phenolic compounds.