Tea Science | Where does the "orchid fragrance" in tea come from? Uncover the mystery of tea aroma

01 What is orchid fragrance?

Orchids, a species of orchidaceae, are known for their gorgeous shapes and attractive aromas. Oriental orchids from subtropical regions, in particular, have been regarded as symbols of traditional virtues throughout the ages for their elegant floral fragrance. However, if a cup of tea could give people an orchid-like aroma, it would greatly enhance consumers' sensory experience and thus increase the economic value of tea. For example, the high-quality oolong tea variety "Anxi Tieguanyin" is known for its distinct orchid aroma [1,2]. Some researchers describe this aroma as similar to the floral scent of jasmine and magnolia, with a hint of fruitiness, and found that this aroma is closely related to the floral scent of orchids [3].

02 Which teas have orchid scent?

For some high-quality green teas, orchid aroma is a rare quality characteristic. Unlike oolong tea, the orchid aroma characteristic in green tea is more gentle, elegant and charming[4].

03 How is the scent of orchid formed?

The intensity of the orchid aroma in tea is directly related to the concentration of methyl jasmonate in tea leaves [3]. Methyl jasmonate is widely present in plants and is one of the most important hormones in plants. It has the functions of attracting insects for pollination, resisting microorganisms and resisting adversity.

04 What factors are related to the formation of orchid fragrance?

Biotic and abiotic stresses increase the accumulation of volatile molecules in tea leaves. During the production of oolong tea, especially during the greening stage, the expression of aroma genes is enhanced, resulting in a significant increase in the concentration of aroma compounds[5]. Other plant stresses, such as light and temperature, can also affect the formation of volatile compounds[6].

Molecular configuration is often also a determining factor in physiological effects. Previous studies have shown that in epi-methyl jasmonate, the isomer with the epi-configuration (1R, 2S) has the highest odor activity [7]. However, the epi-configuration is thermodynamically unstable, so it spontaneously converts to (1R, 2R)-methyl jasmonate at the C-2 position through the enol form [8]. At ambient temperature, the diastereomers reach equilibrium in a ratio of 95:5, which is conducive to the stability of methyl jasmonate [9].

After the fresh leaves are picked, the two configurations of methyl jasmonate continue to be synthesized under the action of enzymes until the accumulation reaches the maximum before the withering stage. With the inactivation of enzymes during the withering stage, methyl jasmonate no longer increases, but at the same time, epi-methyl jasmonate will transform into the configuration of methyl jasmonate. Lower drying temperatures are conducive to retaining the epi-configuration, thereby retaining more orchid aroma in the tea leaves [10].

05 How to maintain the orchid flavor of tea during the tea processing?

During tea processing, appropriate withering time should be given to ensure that endogenous enzymes react fully to synthesize as much methyl jasmonate as possible. At the same time, it should be noted that the withering or drying temperature should not be too high and the processing time should not be too long to avoid converting too much phenotypic methyl jasmonate into methyl jasmonate, thereby retaining more phenotypic configurations to ensure that the orchid flavor in the tea is maintained.

References:

[1] Guo, L., Du, Z., Wang, Z., Lin, Z., Guo, Y., & Chen, M. (2019). Location afffffects fatty acid composition in Camellia sinensis cv Tieguanyin fresh leaves. Journal of Food Science and Technology. https://doi.org/10.1007/s13197-019-04034-8.

[2] Liao, QM (2004). Review on the formation of sensory character of Anxi Tieguanyin. Technology of Tea Science, 3, 35–36.

[3] Feng, Z., et al. (2020). Characterization of the orchid-like aroma contributors in selected premium tea leaves. Food Research International 129.

[4] Li, XB, & Yuan, XA (2010). Shucheng Lanhua tea. China Tea, 11, 20–22.

[5] Zeng, L., Watanabe, N., & Yang, Z. (2018). Understanding the biosyntheses and stress response mechanisms of aroma compounds in tea (Camellia sinensis) to safely and effectively improve tea aroma. Critical Reviews in Food Science and Nutrition, 1–14.

[6] Zhang,

[7] Acree, TE, Nishida, R., & Fukami, H. (1985). Odor thresholds of the stereoisomers of methyl jasmonate. Journal of Agricultural and Food Chemistry, 33(3), 425–427.

[8] Vick, BA, Zimmerman, DC, & Weisleder, D. (1979). Thermal alteration of a cyclic fatty acid produced by a flflaxseed extract. Lipids, 14, 734–740.

[9] Ward, JL, & Beale, MH (1993). Synthesis and biological activity of stereochemically locked derivatives of jasmonic acid. Journal of the Chemical Society, Perkin

[10] Feng, Z., et al. (2023). Formation and isomerization of (Z)-methyl epijasmonate, the key contributor of the orchid-like aroma, during tea processing. Food Research International 172.

Reviewers: Xu Yongquan, Researcher at the Tea Research Institute of the Chinese Academy of Agricultural Sciences, and Liu Xu, Associate Researcher at the Tea Research Institute of the Chinese Academy of Agricultural Sciences