Progress of Tea Aroma Chemistry

Over 60% (w/w), of the components of essential oils from tea were identified before 1960 by classical chemical methods. With the advent of GC and GC-MS, many new compounds were identified, compounds important in contributing to characteristic tea aromas even though present in small concentrations. Now 99.9% (w/w) of the components of essential oils from tea have been determined. With the identification of components and with further improvements in analytical methods, differences in different types of teas and detailed changes in the processing of teas were elucidated. Advanced analytical methods have also made possible the study of stereochemistry of tea aroma compounds. Some of the important optical isomers, such as the structures of linalool, linalool oxides and methyl jasmonate are discussed. Enzymatic studies showed that the main aroma components precursors of black tea are present as glycosides, some of which were separated and identified by the use of HPLC, NMR and FABMS. Synthetic glycosides are used as substrate of glycosidase prepared from fresh tea leaves and primeverosides are hydrolyzable by this enzyme system.