Clarification of Molecular Basis of the Characteristic Aroma Formation in the Formosa Oolong Ted Produced from Tea leaves Infested by the Tea Green Leafhopper

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Oriental Beauty is a flavor-rich oolong tea produced from tea leaves infested by the tea green leafhopper (Jacobiasca formosana) in Taiwan. We have studied to clarify the molecular basis of the characteristic aroma formation of the tea by various approaches such as natural product chemistry, biochemistry, and molecular biology. Oolong tea samples were prepared from tea leaves infeted/noninfested by the insects. Samples were obtained at each step of the manufacturing process and subjected to evaluation tests by professional tea tasters and to GC-MS analysis. The tea produced from tea leaves infested by the insects was found to be superior in the quality and quantity of aroma to that from tea leaves without or with much less the insect attack. Hotrienol and its related compound, 2,6-dimethyl-3.7-octadiene-2,6-diol, were confirmed to be responsible for the insect attack. Genes induced in response to the insect attack and the tea manufacturing processes were identified by the differential screening based on the Megasort analysis. Among them our interests were focused into the genes encoding the stress-responded ones and the amounts of the stress-responded compounds such as raffinose and abscisic acid in tea samples obtained at each step of the tea processing were quantitatively analyzed by HPLC. Both compounds were found to increase dramatically at the solar withering step in good correlation with the expression of the genes responsible for their biosynthesis at the step. These results have revealed that the tea leaves of Oriental Beauty are greatly affected by the stresses of the insect attack and the tea manufacturing processes such as solar withering and turning-over, and these stresses are important factors to increase the production of the aroma compounds characteristic to this characteristic oolong tea.