Effects of baking and aging on the changes of phenolic and volatile compounds in the preparation of old Tieguanyin oolong teas

A series of old oolong teas was prepared by baking fresh Tieguanyin oolong teas at 120-140 °C for 72 h, followed by a long-term storage of 5, 10 and 20 years. To monitor the chemical changes of the tea preparation, phenolic and volatile compounds in a fresh or its newly baked tea were analyzed and compared with those in the three aged teas. The contents of phenolic compounds in the teas were apparently altered by the baking, but remained relatively stable thereafter in the aging process. The contents of major catechin derivatives and flavonol glycosides presumably responsible for astringency and bitterness of teas were reduced while those of gallic acid and gallocatechin gallate, putatively originated from the decomposition and isomerization of (−)-epigallocatechin gallate, were elevated after baking. In contrast, linear and branched hydrocarbons, the abundant volatile compounds in the fresh tea, were relatively stable in the baking process, but nearly diminished during the long-term storage. Relatively minor contents of substituted benzaldehydes and pyrrole derivatives probably rendering the unique flavor of old oolong teas were generated after the baking and aging processes.

► A series of old Tieguanyin oolong teas was prepared by aging after baking. ► Phenolic compounds in the teas were apparently altered by baking, but not aging. ► Volatile linear hydrocarbons in the teas were altered by aging, but not baking. ► Baking and aging are vital processes for the preparation of old oolong teas.