Formation and isomerization of (Z)-methyl epijasmonate, the key contributor of the orchid-like aroma, during tea processing.

The elegant orchid-like fragrance of tea has always been tea processors and consumers' top priority. Controlling the production process is very important for tea aroma formation. This study aims to investigate the synthesis of (Z)-methyl epijasmonate (epi-MeJA), a key contributor to orchid-like aroma properties in tea, during tea processing. The changes in content of epi-MeJA were analysed during the processing of two tea varieties (Anxi Tieguanyin and Taiping Houkui) with typical orchid-like fragrance. It was found to be mainly synthesized and accumulated during tea processing, as fresh tea leaves contained little or even no epi-MeJA. Its content was positively correlated with the processing time in the enzyme active stages (before fixation). During the fixation stages, isomerization occurred due to high temperatures, with a degree of epimerization to the much less odor active isomer (Z)-methyl jasmonate. Isomerization could also occurred during the drying process, which is dominated by the drying temperature.